Quaternary uplift and seismic cycle deformation,
Penı́nsula de Nicoya, Costa Rica
Jeffrey S. Marshall*
Robert S. Anderson
of Earth Sciences and Institute of Tectonics, University of California,
} Department
Santa Cruz, California 95064
ABSTRACT
Differing rates and styles of Quaternary
deformation along the Costa Rican fore arc
reflect segmentation of the trench corresponding with three contrasting domains of
subducting sea floor offshore. Rapid upward
flexure of the southern fore-arc segment results from the subduction of the buoyant
Cocos Ridge, whereas moderate deformation along the central fore-arc segment reflects the subduction of buoyant seamounts.
In contrast, the northern Costa Rican fore
arc deforms in response to the subduction
of relatively dense sea floor devoid of major bathymetric anomalies. Quaternary geomorphic evidence and earthquake oral histories from the Penı́nsula de Nicoya, within
the northern Costa Rican fore arc, demonstrate arcward tilting of the fore-arc crust,
with discrete uplift events occurring during
large subduction earthquakes.
Uplift rates calculated from the late Holocene Cabuya terrace, along the peninsula’s
trench-perpendicular southeastern coast,
decrease systematically toward the arc,
from 4.5 m/k.y. at Cabuya to 1.7 m/k.y. at
Montezuma, 8 km to the northeast. An uplifted carbonate beachrock horizon (radiocarbon age: 4500 –5200 yr B.P.), correlated
between Cabuya and Montezuma, is tilted
0.1& downward toward the arc. Although
Quaternary uplift is evident as far arcward
as Tambor, 10 km northeast of Montezuma,
uplifted terraces are absent between Tambor and the Golfo de Nicoya. A submerged
archaeological site (radiocarbon age: 2500
yr B.P.), located along the Golfo de Nicoya
coast 30 km northeast of Montezuma, demonstrates late Holocene subsidence of 0.5
m/k.y. These data indicate net late Holocene
*Present address: Geosciences Department,
Pennsylvania State University, University Park,
Pennsylvania 16802.
arcward tilting of the peninsula at an angular rotation rate of between 0.01& and
0.02&/k.y.
Oral histories describing the M 7.7
Nicoya subduction earthquake of 5 October
1950 provide evidence of seismic cycle deformation along the peninsula’s southwestern coast between Puerto Carrillo and
Nosara. Interviews with 48 residents show
that coseismic uplift of at least 1 m affected
this coastline, and that a significant fraction of this uplift has subsequently been reversed during four decades of gradual subsidence. The coseismic deformation pattern,
estimated from a uniform slip dislocation
model for the 1950 earthquake, is consistent
with both geomorphic and oral history evidence. These observations suggest that
seismic cycle deformation functions as an
important mechanism of vertical tectonism within the Costa Rican fore arc. Arcward rotation and doming of the Penı́nsula de Nicoya during the Quaternary may
reflect repeated cycles of sudden coseismic deformation followed by gradual postseismic and/or interseismic crustal movement.
INTRODUCTION
The character of the lithosphere subducting along convergent margins largely determines the rates and geometry of tectonism
within the arc and fore-arc regions of the
overriding plate (Cross and Pilger, 1982;
Jarrard, 1986). An excellent example of this
relationship can be observed along the Pacific coast of Costa Rica, where the structurally complex southern Cocos plate subducts beneath the Caribbean plate and the
Panama microplate along the Middle America Trench (Fig. 1). Within ,350 km along
the strike of the trench, stretching from the
Penı́nsula de Nicoya to the Penı́nsula de
Osa, pronounced changes occur in the bathymetry, age, and buoyancy of the subduct-
GSA Bulletin; April 1995; v. 107; no. 4; p. 463– 473; 7 figures; 1 table.
463
ing Cocos plate (Gardner et al., 1987; Protti,
1991).
Considerable attention has been focused
on the rapid fore-arc uplift caused by the
subduction of the buoyant Cocos Ridge beneath the Penı́nsula de Osa (Gardner et al.,
1992; Wells et al., 1988; Corrigan et al., 1990).
However, relatively little is known about the
rates and mechanisms of fore-arc deformation produced by the normal subduction of
denser and smoother sea floor beneath the
Penı́nsula de Nicoya. Because the buoyant
influence of the Cocos Ridge becomes minimal near the Penı́nsula de Nicoya (Gardner
et al., 1992), additional mechanisms must be
invoked to explain the Quaternary uplift observed within the northern Costa Rican fore
arc (Marshall, 1991).
Our goal is to examine Quaternary vertical tectonism on the Penı́nsula de Nicoya
and to explore the role of seismic cycle deformation as a mechanism of net uplift
within the Costa Rican fore arc. First, we
introduce the tectonic setting, stratigraphy,
and structure of the Penı́nsula de Nicoya.
We then discuss the Quaternary uplift history and document the uplift rates of marine
terraces along the peninsula’s southeastern
shoreline. Finally, we apply oral history interviews and dislocation modeling to investigate seismic cycle deformation associated
with the M 7.7 Nicoya subduction earthquake of 1950.
The Penı́nsula de Nicoya represents an
excellent location for this type of study for
several reasons. First, the tectonic framework and Cenozoic history of the Costa
Rican Pacific margin are reasonably well understood. Second, the geometry of the Penı́nsula de Nicoya, with shorelines oriented
both parallel and perpendicular to the Middle America Trench, is ideal for coastal neotectonic analysis. Third, the proximity of the
Penı́nsula de Nicoya to the similarly oriented Penı́nsula de Osa allows comparison
of fore-arc deformation driven by the sub-
MARSHALL AND ANDERSON
Variations in the Subducting Cocos Plate
Figure 1. Tectonic setting of Costa Rica (modified from Protti, 1991). The Cocos, Caribbean, and Panama plates (COCOS, CARIB, and PAN) are outlined by bounding fault
zones: ENFZ, East Nicoya Fracture Zone; WCPB, Western Caribbean-Panama Boundary;
NPDB, North Panama Deformed Belt; SPDB, South Panama Deformed Belt; PFZ, Panama
Fracture Zone; and the Middle America Trench. Convergence rates, shown with direction
arrows, are from DeMets et al. (1990). The three Costa Rican fore-arc segments are
bounded by dashed lines and indicated by letters within circles: N, northern; C, central; and
S, southern. Triangles represent Quaternary volcanoes. Bathymetric contours shown in
meters. Major Pacific Ocean peninsulas, Nicoya and Osa, are shown.
duction of two highly contrasting lithospheric domains. Fourth, the Penı́nsula de
Nicoya lies along a strongly coupled segment of the Middle America Trench that is
subject to repeated large subduction earthquakes (M $ 7.0) and has been designated
a high-probability seismic gap (Güendel,
1986; Nishenko, 1989). The recognition of
seismic cycle deformation within the Nicoya
gap has important implications for our understanding of both the processes of forearc deformation, as well as the repeat times
of potentially damaging earthquakes along
the Costa Rican Pacific coast.
TECTONIC FRAMEWORK
The Costa Rican Fore Arc
The Costa Rican fore arc extends along
the southern Middle America Trench where
464
the Cocos plate subducts northeastward beneath the Caribbean plate and the Panama
microplate (Fig. 1). Recent studies of regional geology (Astorga et al., 1991), seismicity (Güendel and Pacheco, 1992; Goes
et al., 1993; Fan et al., 1993), and fault kinematics (Marshall et al., 1993; Fisher et al.,
1994) within the overriding plates suggest
that the Caribbean-Panama boundary traverses central Costa Rica and intersects the
Pacific coast just southeast of the Penı́nsula
de Nicoya. This boundary separates the
northern Costa Rican fore arc, which belongs to the Caribbean plate, from the central and southern Costa Rican fore-arc
regions, which belong to the Panama microplate. Although this upper-plate boundary
significantly affects tectonism landward of
the fore arc, deformation within the fore arc
itself is controlled principally by the character of the sea floor subducting offshore.
Three distinct domains of subducting sea
floor have been recognized along the Costa
Rican Pacific margin based on contrasts in
age, buoyancy, and bathymetry within the
Cocos plate (Protti, 1991). The sea-floor
thrusting beneath the Penı́nsula de Nicoya,
along the northern Costa Rican fore arc,
consists of typical, relatively dense and
smooth oceanic lithosphere created at the
East Pacific Rise during the late Oligocene
(Hey, 1977; Klitgord and Mammerickx,
1982). In contrast, the sea floor subducting
just southeast of the Penı́nsula de Nicoya,
beneath the central Costa Rican fore arc, is
characterized by buoyant seamounts created
at the Cocos-Nazca boundary during the
early Miocene (Hey, 1977; Lonsdale and
Klitgord, 1978). Farther to the southeast,
the sea floor subducting beneath the Penı́nsula de Osa, within the southern Costa
Rican fore arc, consists of the buoyant
Cocos Ridge generated along the CocosNazca boundary during the middle Miocene
(Hey, 1977; Lonsdale and Klitgord, 1978).
These pronounced contrasts within the subducting Cocos plate produce significant variations in Wadati-Benioff zone geometry
(Güendel, 1986), seismic potential (Protti,
1991), arc volcanism (Malavassi, 1991),
trench morphology (von Huene et al., 1995),
and fore-arc deformation (Gardner et al.,
1992; Wells et al., 1988).
Variations in Fore-Arc Deformation
Since about 1 Ma, subduction of the buoyant Cocos Ridge beneath the Penı́nsula de
Osa has resulted in rapid upward deflection
of the overriding crust within the southern
Costa Rican fore arc (Corrigan et al., 1990;
Gardner et al., 1992). Uplift rates determined from late Quaternary stratigraphy on
the Penı́nsula de Osa range between 6.5
m/k.y. and 2.1 m/k.y., decreasing systematically in an arcward direction across the peninsula (Pinter, 1988). The distribution of
these uplift rates in relation to local faulting
implies that the Penı́nsula de Osa is comprised of arcward tilting blocks with angular
rotation rates varying between 0.038 and
0.068/k.y. (Gardner et al., 1992).
Upward flexure of the overriding crust diminishes with trench-parallel distance from
the axis of the subducting Cocos Ridge
(Corrigan et al., 1990; Gardner et al., 1992).
Although the ridge probably exerts some
tectonic influence on the central Costa
Rican fore arc, geomorphic studies indicate
Geological Society of America Bulletin, April 1995
UPLIFT AND DEFORMATION, PENÍNSULA DE NICOYA, COSTA RICA
Figure 2. Map of the Penı́nsula de Nicoya and adjacent Golfo de Nicoya–Rı́o Tempisque
basin. Mountains, major rivers, and principal towns are indicated. Dark shading represents elevations above 200 m.
that this fore-arc segment deforms principally in response to the subduction of the
buoyant seamounts directly offshore (Wells
et al., 1988). Uplift rates determined from
late Quaternary fluvial terraces along the
central Costa Rican coast range between 0.5
and 3.0 m/k.y. (Drake, 1989).
The flexural uplift model of Gardner et al.
(1992) shows that the Cocos Ridge exerts
minimal tectonic influence within the northern Costa Rican fore arc. The Penı́nsula de
Nicoya therefore deforms principally in response to subduction of relatively dense sea
floor that is devoid of major bathymetric
anomalies. Although a number of authors
have examined Quaternary tectonism on the
peninsula (Alt et al., 1980; Fischer, 1980;
Madrigal and Rojas, 1980; Bergoeing et al.,
1983; Battistini and Bergoeing, 1983; Hare
and Gardner, 1985; Mora, 1985), the rates
and mechanisms of deformation are poorly
constrained. Previous to this study, Quaternary uplift rates have been reported for only
two sites (Fig. 2) on the Penı́nsula de
Nicoya: 2 m/k.y. at Montezuma on the
southeastern coastline (Battistini and Bergoeing, 1983; Mora, 1985), and 1.6 m/k.y. at
Tamarindo near the peninsula’s northwestern tip (Gardner et al., 1992).
ented fore-arc peninsula and basin directly
astride the subducting Cocos Ridge.
The basement of the Penı́nsula de Nicoya
consists of the Jurassic to Cretaceous Nicoya
Complex, an intensely deformed oceanic sequence composed chiefly of pillow basalts,
mafic intrusive rocks, and pelagic sediments
(de Boer, 1979; Kuijpers, 1980; Lundberg,
1982; Baumgartner et al., 1984). Along the
margins of the peninsula, a sequence of Upper Cretaceous to Quaternary marine sediments unconformably overlies the Nicoya
Complex (Lundberg, 1982). An up-section
decrease in depositional depth and structural complexity shows progressive uplift
and deformation of the Penı́nsula de Nicoya
since the beginning of subduction in the
Late Cretaceous (Lundberg, 1982).
The overall structure of the Penı́nsula de
Nicoya consists of a broad anticlinal dome
that crests along the peninsula’s central
mountains and flattens toward its northwestern and southeastern coastlines
(Dengo, 1962; Kuijpers, 1980). Trench-parallel normal faults of Miocene age or
younger may reflect extension resulting
from arching along the Nicoya dome axis
(Kuijpers, 1980). Geomorphic analyses of
drainage basins and remnant erosional surfaces within the central mountains demonstrate continued doming of the peninsula
during the Quaternary (Hare and Gardner,
1985). The Golfo de Nicoya–Rı́o Tempisque
basin most likely represents a synform genetically related to the Nicoya dome (Kuijpers, 1980). This antiform-synform pair is an
emergent portion of the fore-arc structural
high and adjacent basin that extend along
the entire southern Middle America
Trench, between Costa Rica and southern
Mexico (Lundberg, 1982).
QUATERNARY UPLIFT HISTORY
STRATIGRAPHY AND STRUCTURE
The Cobano and Cabuya Terraces
The Penı́nsula de Nicoya (Fig. 2) covers
2400 km2 of the northern Costa Rican fore
arc and lies parallel to both the Middle
America Trench and the northern Costa
Rican volcanic arc (Cordillera de Guanecaste). The peninsula consists of a rugged
linear mountain chain, reaching altitudes
above 900 m, surrounded by a narrow
coastal piedmont. Between the peninsula
and the volcanic arc is an elongate fore-arc
basin containing the Golfo de Nicoya and
the Rı́o Tempisque. This fore-arc morphology is analogous to that along the southern
Costa Rican coast, where the Penı́nsula de
Osa and Golfo Dulce form a similarly ori-
Abundant geomorphic evidence from the
Penı́nsula de Nicoya shows continued vertical tectonism in the northern Costa Rican
fore arc during the Quaternary. Uplifted
marine strandlines record recent emergence
along the peninsula’s seaward-facing coastlines, while submerged strandlines show recent subsidence along much of the peninsula’s landward-facing Golfo de Nicoya coast
(Alt et al., 1980; Marshall, 1991). This juxtaposition of seaward uplift and landward
subsidence suggests arcward rotation or tilting of the peninsula, in a manner similar to
that reported for the Penı́nsula de Osa.
Geological Society of America Bulletin, April 1995
465
MARSHALL AND ANDERSON
Cabuya terrace is cut into the basalts of the
Nicoya Complex and the interbedded sandstones and mudstones of the Cretaceous to
Eocene Cabo Blanco Formation (Lundberg,
1982; Mora, 1985). This surface is blanketed
beneath a 1- to 3-m-thick prograding beach
ridge sequence composed of unconsolidated
well-sorted sands and gravels containing
abundant bivalves, gastropods, and corals
(Calvo, 1983; Chinchilla, 1983; Anderson
et al., 1989). Radiocarbon dating of these
fossils (as discussed below) indicates a minimum late Holocene age for the Cabuya terrace of ca. 5.2 ka (Marshall et al., 1990;
Marshall, 1991).
Uplift Rate Calculations
Nine topographic profiles were surveyed
across the Cabuya terrace, perpendicular to
the modern shoreline, and datable samples
were collected at selected locations (Fig. 3).
Minimum uplift rates were determined for
sample localities using four basic parameters: the modern elevation of the sample,
the original elevation of the sample at deposition, the paleo–sea level at the time of
deposition, and the calibrated radiocarbon
age of the sample. Uplift rates were calculated using the following expression:
Uplift Rate (m/ka) 5
{[Modern Elevation(m)]2
[Depositional Elevation (m)]1
[Paleo-Sea Level (m)]}/Age (ka)
Figure 3. Map of the late Holocene Cabuya marine terrace (shaded area) and the adjacent late Pleistocene Cobano terrace near the towns of Montezuma and Cabuya (solid
squares). Topographic contours shown in meters. Streams appear as shaded lines. Low tide
limit shown by dotted line. Sample locations indicated by numbers (keyed to Table 1 and
Figs. 4 and 5). Circles represent shell samples, and squares represent beachrock. MAT,
Middle America Trench.
Two prominent uplifted Quaternary marine terraces occur along the southeastern
shore of the Penı́nsula de Nicoya between
Cabo Blanco and Tambor (Fig. 3). The upper surface, referred to as the Cobano terrace, consists of a deeply incised coastal
mesa, averaging 180 m in elevation, lying
between the interior mountains and the
abandoned Cobano sea-cliff (Hare and
Gardner, 1985; Mora, 1985). This terrace
is cut into the Montezuma Formation, a
Miocene to Pleistocene transgressive shallow marine sandstone (Lundberg, 1982;
Mora, 1985). Uplift, beginning in the mid-
466
to late Pleistocene, led to emergence of
the Montezuma Formation and erosion of
the Cobano surface during the maximum
late Pleistocene eustatic sea-level highstand (isotope stage 5e) at 125 ka (Mora,
1985).
The lower surface, which we name the
Cabuya terrace, forms the focus of this
study. This terrace consists of a relatively
narrow (,1 km), low-lying (,20 m elevation) wave-cut platform located along the
seaward edge of the Cobano terrace, lying
between the abandoned Cobano sea cliff
and the modern shoreline (Fig. 3). The
The parameters and the calculated uplift
rates for each sample are listed along with
margins of uncertainty in Table 1. These values were determined as follows:
(1) Modern elevation. Present sample elevations were determined by hand level survey relative to the elevation of highest high
tide, visible as the highest recent debris accumulation along the modern shoreline.
These measurements are considered accurate to the nearest 0.2 m. Tidal ranges were
determined based on the tide data of
Borbon (1989).
(2) Depositional elevation. The depositional elevations for shell samples within unconsolidated beach sediments were determined by comparison with similar facies
within the modern beach environment. The
margins of uncertainty reflect the approximate elevation ranges for the appropriate
facies. Beachrock samples were assigned an
original depositional elevation equivalent to
high neap tide (Rodman and Snead, 1982).
Geological Society of America Bulletin, April 1995
UPLIFT AND DEFORMATION, PENÍNSULA DE NICOYA, COSTA RICA
TABLE 1. RADIOCARBON AGES, ELEVATIONS, AND UPLIFT RATES FOR 11 MARINE SHELL AND BEACHROCK
SAMPLES COLLECTED ALONG THE CABUYA TERRACE
Sample
number
Measured
radiocarbon age
(yr B.P.)
(Beta Analytic Inc.)
Calibrated
radiocarbon
(yr B.P.)
Modern
elevation
(m above MSL)
Depositional
elevation
(m above MSL)
Estimated
paleo–mean
sea level
(m below MSL)
Calculated
uplift rate
(m/k.y.)
400 6 60
3800 6 60
2260 6 70
4100 6 100
1530 6 60
780 6 90
490 6 60
4190 6 100
2330 6 70
4690 6 220
1410 6 60
700 6 90
3.7 6 0.2
14.0 6 0.2
9.8 6 0.2
16.5 6 0.2
5.8 6 0.2
4.0 6 0.2
1.5 6 0.5
0. 6 2.0
0 6 2.0
1.5 6 0.5
0 6 2.0
1.5 6 0.5
0
2.0 6 1.0
0.5 6 1.0
2.5 6 1.0
0 6 1.0
0
4.5 6 2.2
3.9 6 0.8
4.4 6 1.6
3.7 6 0.6
4.1 6 2.5
3.6 6 1.6
4935 6 125
5150 6 180
(4852 6 140)
4470 6 110
(4852 6 140)
17.4 6 0.2
15.1 6 0.2
9.0 6 0.2
6.3 6 0.2
4.3 6 0.2
1.0 6 0.5
1.0 6 0.5
1.0 6 0.5
1.0 6 0.5
1.0 6 0.5
3.5 6 1.0
3.5 6 1.0
3.5 6 1.0
2.5 6 1.0
3.5 6 1.0
4.0 6 0.5
3.4 6 0.4
(2.4 6 0.4)
1.7 6 0.4
(1.4 6 0.4)
Shell samples
1
2
3
4
5
6
Beachrock samples
7
8
9
10
11
4390 6 80
4470 6 80
Undated
3980 6 80
Undated
Note: Values and margins of uncertainty were determined as described in text. For undated beachrock samples (9 and 11), values
shown in parentheses represent estimates based on the mean age of the three dated beachrock samples (7, 8, and 10).
(3) Paleo–sea level. Eustatic sea level at
the time of sample deposition is estimated
using the sea-level curve of Pinter and Gardner (1989). This allows comparison of the
uplift rates reported in this study with the
uplift rates determined for the Penı́nsula de
Osa by Gardner et al. (1992). These sealevel estimates have an uncertainty of 61.0 m.
(4) Sample age. Radiocarbon ages were
determined by dating either thick-shelled
gastropod fossils or unweathered samples of
carbonate beachrock. The reported ages are
calibrated radiocarbon ages based on the radiocarbon age calibration curves of Stuiver
and Pearson (1986), Pearson and Stuiver
(1986), and Pearson et al. (1986).
the Cabuya terrace. Calibrated radiocarbon
ages for this horizon range between 4400 yr
B.P. and 5200 yr B.P. Paleo-eustatic sealevel data show that the rapid postglacial
rise in early Holocene eustatic sea level began to slow dramatically near 6.5 ka (Fairbanks, 1989; Chappell and Polach, 1991).
Between 6.5 ka and 5.5 ka the rate of eustatic sea-level rise decreased from .5
m/k.y. to ,1.5 m/k.y. The ages of the three
dated beachrock samples correspond to a
period closely following this significant de-
crease in Holocene eustatic sea-level rise.
The average uplift rates calculated from
these three deposits range between 1.7
m/k.y. and 4.0 m/k.y. Although there is considerable variation in these uplift rates (a
point we address later), they are all less than
the rate of eustatic sea-level rise prior to 6.5
ka and greater than the rate of eustatic sealevel rise since 5.5 ka.
Assuming that the average uplift rates of
the beachrock sites have remained relatively
constant during the late Holocene, it can be
argued that the sudden decrease in the rate
of eustatic sea-level rise between 6.5 and 5.5
ka initiated a local marine regression and
relative emergence of the Cabuya terrace.
This regression led to progressive abandonment of uplifting shorelines and deposition
of the prograding beach ridge sequence that
covers the Cabuya terrace. The Cobano cliff,
between the Cobano and Cabuya terraces
(Fig. 3), therefore, is an abandoned sea cliff
that marks the active shoreline at the beginning of late Holocene emergence.
Arcward Tilting
A plot showing the uplift rates for eleven
sample localities versus trench-perpendicular distance along the Cabuya terrace
(Fig. 4) reveals a systematic arcward decrease in average uplift rates from a maxi-
Late Holocene Emergence
The radiocarbon ages of nine samples collected from the Cabuya terrace systematically increase in age with increasing distance
and elevation away from the modern shoreline (Table 1 and Fig. 3). These ages span
the late Holocene, ranging from 500 yr B.P.
near the shoreline to just over 5000 yr B.P.
near the base of the Cobano cliff. Because
eustatic sea level has been rising or steady
throughout the entire Holocene (Fairbanks,
1989; Chappell and Polach, 1991), the
Cabuya terrace deposits provide evidence
for progressive late Holocene emergence
along this section of coastline and require
rates of crustal uplift that are greater than
the rate of late Holocene eustatic sea-level
rise.
A carbonate beachrock horizon, correlated for over 8 km along the landward edge
of the beach ridge sequence (Fig. 3), is
among the oldest of the shore deposits on
Figure 4. Calculated uplift rates with corresponding error bars for 11 samples along the
Cabuya terrace plotted perpendicular to the Middle America Trench. Sample numbers with
each data point correspond with those in Table 1 and Figure 3. Solid symbols represent
radiocarbon dated samples. Open symbols represent undated beachrock samples assigned
an estimated age based on the mean age of the three dated beachrock samples.
Geological Society of America Bulletin, April 1995
467
MARSHALL AND ANDERSON
Figure 5. Elevations of beachrock samples along the Cabuya terrace plotted perpendicular to the Middle America Trench. Sample numbers with each data point correspond with
those in Table 1 and Figure 3. The best fit line shows an arcward tilt of 0.1& for the
4400 –5200 radiocarbon yr B.P. beachrock strandline.
mum of 4.5 m/k.y. at Isla Cabuya to ,1.7
m/k.y. at Punta Colorada, 8 km to the northeast (Fig. 3). This trend suggests either significant local fault displacement, arcward
tilting of the Cabuya terrace, or some combination of both.
Detailed mapping reveals that the Pleistocene strata of the Montezuma Formation
are affected by only very minor faulting
(Lundberg, 1982; Gursky, 1988). This indicates that the displacements associated with
any late Holocene faulting, along this
stretch of coastline, can be considered negligible with respect to the observed magnitude of late Holocene uplift. The arcward
decrease in uplift rates therefore suggests
late Holocene tilting of the Cabuya terrace
between Isla Cabuya and Punta Colorada.
The spatial distribution of these uplift rates
indicates that arcward tilting has occurred at
an average angular velocity of 0.028/k.y.
Additional evidence for tilting of the
Cabuya terrace is provided by the 4400–5200
radiocarbon yr B.P. beachrock horizon, correlated along the landward edge of the beach
ridge sequence. A plot showing the elevations
of beachrock sites versus trench-perpendicular distance along the coastline (Fig. 5) shows
a systematic decrease in elevation toward the
northeast. This trend corresponds to an arcward tilt of 0.18 and an average angular velocity of rotation of 0.028/k.y. for the late
Holocene.
Arcward tilting of the Cabuya terrace is
consistent with the gentle northeastward dip
(28 to 58) of the upper strata of the Monte-
468
zuma Formation (Madrigal and Rojas, 1980;
Mora, 1985). Assuming a mid-Pleistocene
age for these beds (Sprechmann et al.,
1979), this dip suggests long-term arcward
tilting at an average angular velocity of
,0.018/k.y. However, if this tilting is related
strictly to the latest phase of uplift, which
began sometime between the mid- and late
Pleistocene (Mora, 1985), the average rate
of arcward rotation of these strata could potentially be as high as that calculated for the
late Holocene deposits (0.028/k.y.).
Arcward projection of the decreasing
trend in uplift rates on the Cabuya terrace
predicts a change from uplift to subsidence
6 km northeast of Montezuma in the vicinity
of Tambor (Fig. 2). This location roughly
corresponds with the northeastern margin
of the Cobano and Cabuya terraces. While
beach ridges and minor terraces indicate
Quaternary uplift as far northeast as Tambor (Battistini and Bergoeing, 1983), uplifted terraces are absent along the coast between Tambor and the Golfo de Nicoya.
Whereas the Cabuya terrace experienced
net uplift during the late Holocene, net subsidence affected the peninsula’s Golfo de
Nicoya coast 30 km to the northeast. Archaeological evidence from a submerged
prehistoric burial ground along the Golfo de
Nicoya coast (Guerrero et al., 1991) allows
for the estimation of a subsidence rate for
the late Holocene. The La Regla burial site,
located offshore of the towns of Jicaral and
Lepanto (Fig. 2), is accessible only during
the two lowest spring tides of the year when
it becomes exposed at the extreme low tide
line. Based on tidal data for the Golfo de
Nicoya (Borbon, 1989), we estimate that the
modern elevation of the site is 1.75 m below
mean sea level. Excavated soils indicate that
the site was originally established along the
margins of a coastal mangrove with an elevation just above mean sea level. An artifact
from La Regla yielded a radiocarbon age of
2472 6 70 yr B.P. (Guerrero et al., 1991). At
2.5 ka, mean sea level is estimated at 0.5 m
lower than modern sea level (Pinter and
Gardner, 1989). Therefore, total subsidence
at La Regla since 2.5 ka is roughly 1.25 m,
having occurred at an average rate of ;0.5
m/k.y.
If, as a rough approximation, the entire
Penı́nsula de Nicoya is modeled as a single
arcward rotating block, then the rates of vertical tectonism along the seaward and landward coastlines can be used to estimate the
angular velocity of arcward rotation. A comparison of the subsidence rate at La Regla
with the uplift rate of a sample of similar age
at Cabuya (sample no. 4, uplift rate: 4.4
m/k.y.) indicates an approximate minimum
angular velocity of arcward rotation for the
entire peninsula of ;0.018/k.y. for the late
Holocene.
It is likely, however, that a single-block
model for the entire peninsula is an oversimplification. Although Quaternary faulting is minimal within the Cobano and
Cabuya terraces (Lundberg, 1982; Gursky,
1988), their southwestern margin is delineated by a significant trench-parallel normal
fault (Fig. 3). This feature suggests that the
Cabuya and Cobano terraces may occupy an
individual fault-bounded block situated
within the larger structural framework of the
peninsula’s entire southeastern coastline.
Similar trench-parallel normal faults, found
throughout the peninsula (Kuijpers, 1980),
may represent boundaries of discrete fault
blocks that rotate semi-independently at different angular velocities. Gardner et al.
(1992) proposed this type of model for deformation of the Penı́nsula de Osa. Further
detailed analysis of Quaternary faulting and
vertical tectonism is required before such a
model can be applied conclusively to the
Penı́nsula de Nicoya.
Tectonic Implications
Late Quaternary arcward tilting along the
Penı́nsula de Nicoya’s southeastern coastline is consistent with regional geomorphic
evidence documenting emergence along the
peninsula’s Pacific coastlines and submer-
Geological Society of America Bulletin, April 1995
UPLIFT AND DEFORMATION, PENÍNSULA DE NICOYA, COSTA RICA
gence along the peninsula’s Golfo de Nicoya
coast. As discussed earlier, several authors
have modeled the long-term deformational
structure of the Penı́nsula de Nicoya as a
large anticline or dome (Dengo, 1962; Kuijpers, 1980; Lundberg, 1982; Hare and Gardner, 1985). The evidence presented in this
study suggests that this dome structure has
been rotating in an arcward direction during
the Quaternary at an average angular velocity ranging between 0.018 and 0.028/k.y.
These rotation rates for the Penı́nsula de
Nicoya are consistent with those of Gardner
et al. (1992), who reported Quaternary arcward tilting of fault-bounded blocks on the
Penı́nsula de Osa at angular velocities
ranging between 0.038 and 0.068/k.y. The
higher rates of uplift and rotation observed
on the Penı́nsula de Osa can be attributed to
the upward flexure caused by subduction of
the buoyant Cocos Ridge directly beneath
the peninsula. Because the Cocos Ridge exerts minimal tectonic influence on the Penı́nsula de Nicoya (Gardner et al., 1992), additional mechanisms of uplift must be
invoked to explain the deformation rates
documented in this study for the peninsula’s
southeastern shore.
The proximity of this coastline to the
northwestern margin of the central Costa
Rican fore arc (Fig. 1), which deforms in
response to buoyant seamount subduction
(Wells et al., 1988), leads to speculation that
these rates may be anomalously high and are
not representative of the deformation affecting the peninsula as a whole. The oversteepened trench slope offshore of Cabo
Blanco may have developed due to localized
rapid uplift related to subduction of the
buoyant Fisher seamount immediately to
the southeast of the peninsula (von Huene
et al., in press). A flexural uplift model, similar to that developed for the Cocos Ridge
(Gardner et al., 1992), may be applicable for
the subducting Fisher seamount and, hence,
the vertical deformation observed along the
southeastern coastline of the Penı́nsula de
Nicoya.
On the other hand, oblique slip along
northeast-trending faults of the East Nicoya
Fracture Zone (Fig. 1), which form part of
the Caribbean-Panama boundary (Marshall
et al., 1993; Fisher et al., 1994), may effectively insulate the Penı́nsula de Nicoya from
vertical deformation related to seamount
subduction to the southeast. In either case,
the deformation affecting the majority of the
Penı́nsula de Nicoya should principally reflect subduction of the relatively dense and
smooth sea floor directly offshore.
Seismic reflection imaging of the trench
slope offshore of the Penı́nsula de Nicoya
indicates that underplating may play a significant role in accretionary prism development and long-term passive uplift along the
northern Costa Rican fore arc (Silver et al.,
1985; Shipley and Moore, 1986; Shipley
et al., 1992). Additionally, several authors
have suggested that recent uplift on the Penı́nsula de Nicoya may have been accomplished during discrete coseismic events associated with repeated earthquakes along
this highly coupled segment of the Middle
America Trench (Fischer, 1980; Battistini
and Bergoeing, 1983; Anderson et al., 1989;
Marshall et al., 1990; Marshall, 1991). These
two processes, operating independently or
concurrently, both represent likely mechanisms of ‘‘steady state’’ vertical tectonism
produced by the subduction of relatively
dense and bathymetrically smooth lithosphere beneath the northern Costa Rican
fore arc.
SEISMIC CYCLE DEFORMATION
Penı́nsula de Nicoya Earthquakes
Popular legends and historical documents
from the Penı́nsula de Nicoya describe the
recurrence of severe earthquakes spanning
at least the past three centuries (GonzálezVı́quez, 1910; Pittier, 1959; Marshall, 1991).
During the present century, seismographic
networks have recorded at least five large
subduction earthquakes (M $ 7.0) in the
vicinity of the Penı́nsula de Nicoya (Fig. 6;
Güendel, 1986; Protti, 1991, 1994). Two of
these events (5 October 1950, M 5 7.7, and
23 August 1978, Ms 5 7.0) were centered
directly beneath the peninsula and ruptured
the northern Costa Rican segment of the
Middle America Trench.
With a relatively rapid convergence rate
of 9.1 cm/yr along this segment of the trench
(DeMets et al., 1990), it is unlikely that the
Ms 7.0 1978 earthquake released all of the
strain accumulated since the much larger M
7.7 1950 event (Güendel, 1986). Nishenko
(1989) gives a 93% probability of a M 7.4
earthquake on the Penı́nsula de Nicoya before the year 2009, listing it as fourth among
the top seismic gaps in the circum-Pacific
region.
Substantial vertical tectonism associated
with large subduction earthquakes has been
reported in a variety of fore-arc settings
around the world (e.g., Plafker, 1972; Matsuda et al., 1978; Thatcher, 1984; Taylor
et al., 1980, 1987; Carver et al., 1994). In
order to explore the possibility of seismic
cycle deformation within the northern Costa
Rican fore arc, we focused our investigation
on the M 7.7 Nicoya earthquake of 1950.
The 1950 Earthquake: Oral History Study
Although records from this event show
that significant damage occurred in Costa
Rica’s capital city of San José and in the
Pacific port of Puntarenas (Louderback,
1951; Miyamura, 1980), there exists no systematic documentation of earthquake effects on the Penı́nsula de Nicoya. In similar
cases, where rigid field data is lacking, other
researchers have effectively used anecdotal
evidence to document the geologic effects of
past earthquakes (e.g., Lyell, 1849; Dutton,
1889; Plafker, 1969; Allen, 1974; Taylor
et al., 1980, 1987; Güendel et al., 1989).
On the basis of these examples, we interviewed 48 residents of the central Pacific
coast of the Penı́nsula de Nicoya who experienced the 1950 earthquake. Interviews
were conducted along a 25 km stretch of
coastline between the towns of Puerto Carrillo and Nosara (Fig. 2), located within the
1950 rupture zone (Fig. 6). As in the coseismic uplift studies of Plafker (1969) and of
Taylor et al. (1980, 1987), we focused specifically on coastal residents who were intimately familiar with the local tidal levels and
coastal landmarks at the time of the
earthquake.
Interpretation of these interviews naturally involves considerable uncertainty regarding the accuracy of elderly people recalling an event that occurred nearly 40 yr
previously. However, rural Nicoya society
boasts a strong oral tradition, and many of
these people, as farmers and fishermen, are
keen observers of their surroundings. It is
clear from the interviews that the 1950
earthquake represents one of the most spectacular events in the lives of older peninsula
residents. Many of those interviewed were
able to recall minute details of the experience, and in most cases, uncertainty is
greatly reduced by corroboration between
several different interviews.
Relative Sea-Level Changes
The interviews indicate that ground shaking intensities throughout the Penı́nsula de
Nicoya reached at least VII on the Modified
Mercalli Scale (Wood and Neumann, 1931)
and probably ranged as high as IX or X in
alluvium and along beaches. Ground cracking, landslides, liquefaction, and building
Geological Society of America Bulletin, April 1995
469
MARSHALL AND ANDERSON
Figure 6. Locations of
five recent large subduction earthquakes (M $
7.0) centered near the
Penı́nsula de Nicoya.
Stars represent epicenters. Shaded area within
solid line is aftershock
area for the 1950 event.
Dashed lines enclose aftershock areas for the
1978 and 1990 events.
D a t a f r o m G ü e n d e l
(1986) and Protti (1991,
1994).
damage were widespread (Marshall, 1991).
All of the interview participants who lived or
worked in 1950 along the central Nicoya
coast between Nosara and Puerto Carrillo
mentioned a significant drop in sea level associated with the earthquake. Residents of
Sámara remember scouring the newly exposed sea floor just after the earthquake collecting an abundance of fish left stranded by
the sudden retreat of the sea. Many people
explained that for many years after the
earthquake it was possible to walk to sites
that previously had been inaccessible along
the rocky cliffs typical of that stretch of
coastline.
Nearly all of the coastal residents also indicated that relative sea level has been gradually rising along the central Nicoya coast
since the 1950 earthquake. Reportedly, the
sea has slowly reclaimed many of the sites
that were exposed by its sudden coseismic
retreat. Several suggested that this apparent
sea-level rise occurred fairly rapidly during
the first several years after the earthquake
but since then has slowed noticeably.
The approximate magnitude of relative
sea-level changes associated with the 1950
earthquake can be estimated based on observations at well-known coastal landmarks.
For example, when asked about specific sites
where the sea-level changes were obvious,
two fishermen from Nosara both independently referred to a rocky headland known
locally as El Raspa Nalgas (‘‘The Butt
Scratcher’’). Prior to the 1950 earthquake,
this site represented a barrier to foot passage around Punta Nosara. Even during the
lowest tides of the year, deep water at this
site prohibited walking along the shoreline.
470
However, after the earthquake it was possible to walk around this rocky point at low
tide without entering the water. These observations suggest a coseismic drop in relative sea level at this site of at least the height
of a person’s waist, or roughly 1 m.
According to both of the fishermen, relative sea level at El Raspa Nalgas has been
rising gradually since 1950 but still remains
lower than it was prior to the earthquake.
One of these men indicated that the water at
this site is now knee deep at low tide. This
suggests a recovery of relative sea level at
this site of at least 0.5 m since the earthquake.
In another example, coastal residents
along the bays of Sámara and Puerto Carrillo estimated that the high tide level after
the earthquake was near present-day low
tide. Currently, tidal levels in these bays are
reportedly similar or somewhat higher than
they were prior to the earthquake, following
a progressive rise in relative sea level during
the past four decades. These observations
suggest a coseismic drop in relative sea level,
followed by a gradual recovery, of a magnitude similar to the average difference between high and low tide, or ;2 m (Borbon,
1989).
Tectonic Implications
The observations of relative sea-level
changes associated with the 1950 earthquake suggest the occurrence of coseismic
uplift ranging from 1 to 2 m along the coast
between Nosara and Puerto Carrillo
(Fig. 2). Although observable uplift may
have occurred as far south as Puerto Coyote,
residents of Cabuya, on the peninsula’s
southeastern coast, recall no change in relative sea level. The interviews also suggest
that a significant fraction of the coseismic
uplift has been reversed during a subsequent
long-term period of gradual postseismic
and/or interseismic subsidence that may
continue through the present.
These apparent vertical tectonic displacements most likely reflect a single episode in
a recurring seismic cycle of crustal deforma-
Figure 7. a. Contour map of coseismic vertical deformation estimated from a uniformslip-planar dislocation model for the 1950 M 7.7 Nicoya subduction earthquake. Uplift and
subsidence shown in meters. Dashed lines show locations of cross sections shown in Figure 7b. Model parameters based on seismicity data from Güendel (1986).
Geological Society of America Bulletin, April 1995
UPLIFT AND DEFORMATION, PENÍNSULA DE NICOYA, COSTA RICA
tion within the northern Costa Rican fore
arc related to underthrusting of the subducting Cocos plate beneath the Penı́nsula de
Nicoya. The initial coseismic uplift resulted
from elastic rebound of the fore-arc crust
produced by sudden failure along the thrust
interface (e.g., Plafker, 1972; Thatcher,
1984). The subsequent period of progressive
subsidence represents gradual modification
of the coseismic displacements by the combined effects of postseismic downdip rupture propagation (e.g., Brown et al., 1977;
Barrientos et al., 1992), postseismic viscoelastic readjustments within the asthenosphere (e.g., Nur and Mavko, 1974; Thatcher
and Rundle, 1984), and/or interseismic elastic strain accumulation within the fore-arc
crust (e.g., Plafker, 1972; Thatcher, 1984).
Dislocation Model
To develop an estimate of the coseismic
deformation pattern resulting from the 1950
earthquake, we applied the uniform slip planar dislocation modeling techniques of
Mansinha and Smylie (1971). Model param-
eters were estimated using the seismicity
data of Güendel (1986) and the relationships between surface wave magnitude, seismic moment, mean slip, and rupture area
discussed by Purcaru and Berckhemer
(1978) and Scholz (1990).
Although the modeled deformation pattern (Figs. 7a and 7b) only represents a general approximation, it is consistent with the
distribution and magnitude of coseismic uplift indicated by the oral history interviews.
The model shows that a 1950 type earthquake within the northern Costa Rican fore
arc is capable of producing coseismic uplift
on the order of 1.0 m along the central Pacific coast of the Penı́nsula de Nicoya and
subsidence on the order of 0.3 m along the
axis of the Golfo de Nicoya–Rı́o Tempisque
depression. The magnitude of this deformation decreases toward the northwest and
southeast, forming an elongate dome pattern centered along the Pacific coast of the
peninsula flanked by an elongate depression
centered along the Golfo de Nicoya.
In other fore-arc regions, researchers
have demonstrated the connection between
net Quaternary deformation, expressed by
geomorphology and structure, and the repetition of the seismic deformation cycle
(e.g., Plafker, 1972; Matsuda et al., 1978;
Taylor et al., 1980, 1987; Thatcher, 1984;
Atwater, 1987). The coseismic deformation
pattern estimated by the dislocation model
bears a striking resemblance to the dome
pattern proposed for the long-term deformation of the Penı́nsula de Nicoya. The dislocation model, however, places maximum
uplift along the peninsula’s seaward coastline, whereas structural and geomorphic
data indicate maximum net uplift along the
crest of the peninsula’s interior mountain
range (Dengo, 1962; Kuijpers, 1980; Hare
and Gardner, 1985).
If long-term doming of the peninsula is
related to seismic cycle deformation, this
discrepancy can be reconciled by the postseismic redistribution of vertical displacements by either downdip fault creep (e.g.,
Brown et al., 1977; Barrientos et al., 1992) or
viscoelastic flow within the asthenosphere
(e.g., Nur and Mavko, 1974; Thatcher and
Rundle, 1984). Either of these processes
Figure 7. b. Cross sections A–D through the estimated coseimic deformation pattern (Fig. 7a). Approximate Pacific coast locations are
indicated.
Geological Society of America Bulletin, April 1995
471
MARSHALL AND ANDERSON
could migrate the focus of maximum uplift
landward from the trench and produce gradual subsidence in the region of maximum
coseismic uplift. These readjustments, coupled with interseismic strain accumulation,
may explain the anecdotal observations of a
coseismic drop in sea level followed by several decades of gradual sea-level recovery.
Net Quaternary vertical tectonism in the
vicinity of both the Penı́nsula de Nicoya and
the Penı́nsula de Osa is characterized by
pronounced uplift along a trench-parallel
arcward tilting peninsula and subsidence
along a gulf or fluvial lowland located landward of the peninsula. The striking resemblance between this pattern and the elastic
coseismic deformation pattern commonly
attributed to subduction earthquakes leads
to speculation that the repetition of seismic
cycle deformation may operate as an important mechanism of net vertical tectonism
within both the northern and southern
Costa Rican fore-arc regions. Both of these
regions are known sources of large subduction earthquakes (M $ 7.0) with estimated
recurrence intervals of ;40 yr (Güendel,
1986). Repetition of seismic cycle deformation at this frequency potentially could produce a significant component of net vertical
tectonism.
CONCLUSIONS
Variations in the rates and styles of Quaternary deformation along the Costa Rican
fore arc reflect contrasts in the age, buoyancy, and bathymetry of the subducting
Cocos plate offshore. Three fore-arc segments can be identified that correlate with
the three distinct domains of subducting sea
floor described by Protti (1991). Within the
southern Costa Rican fore arc, subduction
of the buoyant Cocos Ridge causes rapid upward deflection and arcward tilting of the
Penı́nsula de Osa (Corrigan et al., 1990;
Gardner et al., 1992). Along the central
Costa Rican fore arc, the influence of the
Cocos Ridge diminishes and deformation
results principally from subduction of buoyant seamounts (Wells et al., 1988). Within
the northern Costa Rican fore arc, the influence of the Cocos Ridge becomes nonexistent (Gardner et al., 1992) and deformation of the Penı́nsula de Nicoya is driven
by the subduction of relatively dense and
bathymetrically smooth sea floor.
Geomorphic evidence from the Penı́nsula
de Nicoya indicates Quaternary emergence
along its seaward coastlines and submergence along the landward Golfo de Nicoya
472
coast. Late Holocene uplift rates, calculated
from beach ridge deposits on the Cabuya
marine terrace, decrease systematically
toward the northeast from 4.5 m/k.y. at
Cabuya to ,1.7 m/k.y. at Montezuma.
Whereas Quaternary uplift is evident along
the southeast coast as far arcward as Tambor, uplifted terraces are absent between
Tambor and the Golfo de Nicoya. Archaeological evidence from the Golfo de Nicoya
coast indicates late Holocene subsidence at
a rate of 0.5 m/k.y. These data suggest net
late Holocene arcward tilting of the Penı́nsula de Nicoya at an average angular rotation rate ranging between 0.018 and 0.028/
k.y. Arcward rotation at this rate is consistent
with the gentle northeastward tilt of both a
late Holocene beachrock horizon on the
Cabuya terrace and the adjacent Pleistocene
strata of the Montezuma Formation. Arcward tilting of the Penı́nsula de Nicoya may
be accomplished by the rotation of a system
of semi-independent fault-bounded blocks.
Oral histories describing the M 7.7 Nicoya
subduction earthquake of 5 October 1950
provide evidence of seismic cycle deformation along the southwestern coast of the
Penı́nsula de Nicoya. Interviews with 48 residents indicate that coseismic uplift of at
least 1 m affected the coastline between
Puerto Carrillo and Nosara, and that a significant fraction of this uplift has been reversed during the following four decades by
gradual subsidence.
The coseismic deformation pattern estimated by a dislocation model for the 1950
earthquake is consistent with both the geomorphic and the oral history evidence.
These observations suggest that seismic cycle deformation functions as an important
mechanism of vertical tectonism within the
northern Costa Rican fore arc. Net Quaternary arcward rotation and doming of the
Penı́nsula de Nicoya may reflect repeated
cycles of coseismic deformation followed by
gradual modification of the coseismic deformation field by postseismic and/or interseismic crustal movements.
Quaternary vertical tectonism within the
Costa Rican fore arc traditionally has been
attributed to upward flexure produced by
the subduction of buoyant bathymetric features such as the Cocos Ridge and adjacent
seamounts offshore of southern and central
Costa Rica. However, this mechanism alone
is inadequate to explain Quaternary deformation observed on the Penı́nsula de Nicoya
in the northern Costa Rican fore arc. Net
Quaternary deformation along the entire
Costa Rican fore arc probably reflects im-
portant contributions from seismic cycle deformation and accretionary processes such
as underplating and subduction erosion.
ACKNOWLEDGMENTS
This investigation was initiated based on
the suggestions of Karen McNally of the
University of California, Santa Cruz,
Charles Richter Seismological Laboratory.
Research was conducted in cooperation
with the Observatorio Volcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA). We gratefully
acknowledge their entire staff for logistical
support and for ideas incorporated into this
paper. Special thanks is owed to Jorge
Brenes M. for his insightful assistance both
in field work and in conducting oral history
interviews. We are especially indebted to the
gracious people of the Penı́nsula de Nicoya
for allowing access onto their lands and into
their lives.
We would also like to thank Gary Griggs,
Nicholas Pinter, and William Lettis for helpful reviews of earlier versions of this manuscript. Funding was provided by a University
of California, Santa Cruz Seed Fund grant
to Robert Anderson and Karen McNally.
Radiocarbon dating was conducted by Beta
Analytic Inc.
REFERENCES CITED
Allen, C. R., 1975, Geological criteria for evaluating seismicity:
Geological Society of America Bulletin, v. 86, p. 1041–1057.
Alt, J. N., Harpster, R. E., and Schwartz, D. P., 1980, Late Quaternary deformation and differential uplift along the Pacific
coast of Costa Rica: Geological Society of America Abstracts with Programs, v. 12, p. 378–379.
Anderson, R. S., Marshall, J. S., and Brenes Marin, J. A., 1989,
Evidence of repeated coseismic uplift along the southern
coast of Nicoya peninsula, Costa Rica: Geological Society of
America Abstracts with Programs, v. 21, no. 6, p. A92.
Astorga, A., Fernández, J. A., Barboza, G., Campos, L., Obando,
J., Aguilar, A., and Obando, L. G., 1991, Cuencas sedimentarias de Costa Rica: Evolución geodinámica y potencial de
hidrocarburo: Revista Geológica de América Central, v. 13,
p. 25–59.
Atwater, B. F., 1987, Evidence for great Holocene earthquakes
along the outer coast of Washington State: Science, v. 236,
p. 942–944.
Barrientos, S. E., Plafker, G., and Lorca, E., 1992, Postseismic
coastal uplift in southern Chile: Geophysical Research Letters, v. 19, p. 701–704.
Battistini, R., and Bergoeing, J. P., 1983, Reconnaissance géomorphologique de la façade Pacifique du Costa Rica: Geomorphologie Littorale, Travaux et Documents de Géographie
Tropicale, CEGET, v. 49, 73 p.
Baumgartner, P. O., Mora, C. R., Butterlin, J., Sigal, J., Glacon,
G., Azema, J., and Bourgois, J., 1984, Sedimentación y paleogeografı́a del Cretócio y Cenozóico del litoral Pacı́fico de
Costa Rica: Revista Geológica de América Central, v. 1,
p. 57–136.
Bergoeing, J. P., Brenes, L. G., and Malavassi, E., 1983, Geomorphologı́a del Pacifı́co norte de Costa Rica (Explicaciı́n del
mapa geomorfológico 1:100,000): San José, Costa Rica,
Ministerio de Obras Públicas y Transporte (MOPT)–Instituto Geográfico Nacional (IGN), and Universidad de Costa
Rica (UCR)–Departamento de Geografı́a, 110 p.
Borbon, A., 1989, Tabla de mareas, Costa del Pacı́fico, Costa Rica:
San José, Costa Rica, A. Borbon & CIA, S.A., 14 p.
Brown, L., Reilinger, R., Holdbahl, S. R., and Balazs, E. I., 1977,
Postseismic crustal uplift near Anchorage, Alaska: Journal
of Geophysical Research, v. 82, p. 3369–3378.
Calvo, C., 1983, Geologı́a de Cabuya y la parte este de la Reserva
Natural Absoluta de Cabo Blanco, Costa Rica [Informe Final, Campaña Geológica]: San José, Costa Rica, Escuela
Geological Society of America Bulletin, April 1995
UPLIFT AND DEFORMATION, PENÍNSULA DE NICOYA, COSTA RICA
Centroamericana de Geologı́a, Universidad de Costa Rica,
41 p.
Carver, G. A., Jayko, A. S., Valentine, D. W., and Li, W. H.,
1994, Coastal uplift associated with the 1992 Cape Mendecino earthquake, northern California: Geology, v. 22,
p. 195–198.
Chappell, J., and Polach, H., 1991, Post-glacial sea-level rise from
a coral record at Huon Peninsula, Papua New Guinea: Nature, v. 349, p. 147–149.
Chinchilla, A. L., 1983, Geologı́a del area de Montezuma y alrededores, Penı́nsula de Nicoya, Provincia de Puntarenas,
Costa Rica [Informe Final, Campaña Geológica]: San José,
Costa Rica, Escuela Centroamericana de Geologı́a, Universidad de Costa Rica, 50 p.
Corrigan, J., Mann, P., and Ingle, J. C., 1990, Forearc response to
subduction of the Cocos Ridge, Panama–Costa Rica: Geological Society of America Bulletin, v. 102, p. 628– 652.
Cross, T. A., and Pilger, R. H., 1982, Controls of subduction geometry, location of magmatic arcs, and tectonics of arc and
back arc regions: Geological Society of America Bulletin,
v. 93, p. 545–562.
de Boer, J., 1979, The outer arc of the Costa Rica orogen (oceanic
basement complexes of the Nicoya and Santa Elena peninsulas): Tectonophysics, v. 56, p. 221–259.
DeMets, C., Gordon, R. G., Argus, D. F., and Stein, S., 1990,
Current plate motions: Geophysics Journal International,
v. 101, p. 425– 478.
Dengo, G., 1962, Estudio geológico de la región de Guanecaste,
Costa Rica: San José, Costa Rica, Instituto Geográfico Nacional, 113 p.
Drake, P. G., 1989, Quaternary geology and tectonic geomorphology of the coastal piedmont and range, Puerto Quepos area,
Costa Rica [M.S. thesis]: Albuquerque, New Mexico, University of New Mexico, 183 p.
Dutton, C. E., 1889, The Charleston earthquake of August 31,
1886: U.S. Geological Survey, Ninth Annual Report,
p. 203–528.
Fairbanks, R. G., 1989, A 17,000-year glacio-eustatic sea level
record: Influence of glacial melting rates on the Younger
Dryas event and the deep-ocean circulation: Nature, v. 342,
p. 637– 642.
Fan, G. W., Beck, S. L., and Wallace, T. C., 1993, The seismic
source parameters of the 1991 Costa Rica aftershock sequence: Evidence for a transcurrent plate boundary: Journal
of Geophysical Research, v. 98, p. 15759 –15778.
Fischer, R., 1980, Recent tectonic movements of the Costa Rican
Pacific coast: Tectonophysics, v. 70, p. T25–T33.
Fisher, D. M., Gardner, T. W., Marshall, J. S., and Montero, P. W.,
1994, Kinematics associated with late Cenozoic deformation
in central Costa Rica: Western boundary of the Panama
microplate: Geology, v. 22, p. 263–266.
Gardner, T. W., and 11 others, 1987, Central America and the
Caribbean, in Graf, W. L., ed., Geomorphic systems of
North America: Geological Society of America Centennial
Special Volume 2, p. 343– 402.
Gardner, T. W., Verdonck, D., Pinter, N. M., Slingerland, R.,
Furlong, K. P., Bullard, T. F., and Wells, S. G., 1992, Quaternary uplift astride the aseismic Cocos Ridge, Pacific
coast, Costa Rica: Geological Society of America Bulletin,
v. 104, p. 219–232.
Goes, S. D., Velasco, A. A., Schwartz, S. Y., and Lay, T., 1993, The
April 22, 1991, Valle de la Estrella, Costa Rica (Mw 5 7.7)
earthquake and its tectonic implications: A broadband seismic study: Journal of Geophysical Research, v. 98B5,
p. 8127– 8142.
González-Vı́quez, C., 1910, Temblores, terremotos, inundaciones
y erupciones volcánicas en Costa Rica, 1608 –1910: San José,
Costa Rica, Tipografı́a de Avelino Alsina, 200 p.
Güendel, F., 1986, Seismotectonics of Costa Rica: An analytical
view of the southern terminus of the Middle America
Trench [Ph.D. dissert.]: Santa Cruz, California, University
of California, 157 p.
Güendel, F., and Pacheco, J., 1992, The 1990 –1991 seismic sequence across central Costa Rica: Evidence for the existence of a micro-plate boundary connecting the Panama
Deformed Belt and the Middle America Trench [abs.]: Eos
(Transactions, American Geophysical Union), v. 73, p. 399.
Güendel, F., Montero, C., Rojas, D., Brenes, J., Segura, J., Sáenz,
R., and González, V., 1989, Informe sobre el enjambre sismico ocurrido cerca de la ciudad de Orotina entre el 21 y el
24 de Enero de 1989: Boletı́n Sismológico, Observatorio
Vulcanológico y Sismológico de Costa Rica, Universidad
Nacional (OVSICORI-UNA), v. 5.
Guerrero, J. V., Vázquez, R., and Solano, F., 1991, Entierros secundarios y restos organicos de ca. 500 A.C. preservados en
una area de inundacion marina, Golfo de Nicoya, Costa
Rica: Vı́nculos: Revista de Antropologı́a del Museo Nacional de Costa Rica, v. 17, p. 17–51.
Gursky, M., 1988, Análisis tectónico de la Penı́nsula de Nicoya
(Costa Rica) y su significado para el desarollo estructuralgeodinámico de América Central meridional: Revista Geológica de América Central, v. 8, p. 19–75.
Hare, P. W., and Gardner, T. W., 1985, Geomorphic indicators of
vertical neotectonism along converging plate margins,
Nicoya Peninsula, Costa Rica, in Morisawa, M., and Hack,
J. T., eds., Tectonic geomorphology: Proceedings, Geomorphology Symposia Series, 15th, Binghamton, p. 76–104.
Hey, R. N., 1977, Tectonic evolution of the Cocos-Nazca spreading
center: Geological Society of America Bulletin, v. 88,
p. 1404 –1420.
Jarrard, R. D., 1986, Relations among subduction parameters: Reviews of Geophysics, v. 24, p. 217–284.
Klitgord, K. D., and Mammerickx, J., 1982, Northern East Pacific
Rise: Magnetic anomaly and bathymetric framework: Journal of Geophysical Research, v. 87, p. 6725– 6750.
Kuijpers, E. P., 1980, The geologic history of the Nicoya ophiolite
complex, Costa Rica, and its geotectonic significance: Tectonophysics, v. 68, p. 233–255.
Lonsdale, P., and Klitgord, K. D., 1978, Structure and tectonic
history of the eastern Panama basin: Geological Society of
America Bulletin, v. 89, p. 981–999.
Louderback, G. D., 1951, Seismological notes: Bulletin of the Seismological Society of America, v. 41, p. 68.
Lundberg, N., 1982, Evolution of the slope landward of the Middle
America Trench, Nicoya Peninsula, Costa Rica, in Legget,
J. K., ed., Trench-forearc geology: Geological Society of
London Special Publication 10, p. 131–147.
Lyell, C., 1849, Second visit to the United States of North America,
Volume 2: New York, Harper and Brothers, 172 p.
Madrigal, R., and Rojas, E., 1980, Manual descriptivo del mapa
geomorfologico de Costa Rica (escala 1:200,000): San José,
Costa Rica, Secretarı́a Ejecutı́va de Planificación Sectorial
Agropecuaria y de Recursos Naturales Renovables
(SEPSA), 79 p.
Malavassi, E., 1991, Magma sources and crustal processes at the
southern terminus of the Middle American volcanic arc
[Ph.D. dissert.]: Santa Cruz, California, University of California, 457 p.
Mansinha, L., and Smylie, D. E., 1971, The displacement fields of
inclined faults: Geological Society of America Bulletin,
v. 61, p. 1433–1440.
Marshall, J. S., 1991, Neotectonics of the Nicoya Peninsula, Costa
Rica: A look at forearc response to subduction at the Middle
America Trench [Master’s thesis]: Santa Cruz, California,
University of California, 196 p.
Marshall, J. S., Anderson, R. S., and Brenes, J., 1990, Geomorphic
evidence and oral histories from coastal Nicoya Peninsula,
Costa Rica, reveal crustal response to subduction at the
Middle America trench: Programas y Resumenes de Ponencias, VII Congreso Geológico de América Central,
19 –23 de Noviembre, 1990, San José, Costa Rica, Abstract
No. 31.
Marshall, J. S., Fisher, D. M., and Gardner, T. W., 1993, Western
margin of the Panama microplate, Costa Rica: Kinematics
of faulting along a diffuse plate boundary: Geological Society of America Abstracts with Programs, v. 25, no. 6,
p. A284.
Matsuda, T., Ota, Y., Ando, M., and Yonekura, N., 1978, Fault
mechanism and recurrence time of major earthquakes in
southern Kanto district, Japan, as deduced from coastal terrace data: Geological Society of America Bulletin, v. 89,
p. 1610 –1618.
Miyamura, S., 1980, Sismicidad de Costa Rica: San José, Costa
Rica, Editorial Universidad de Costa Rica, 190 p.
Mora, C. R., 1985, Sedimentologı́a y geomorfologı́a del sur de la
Penı́nsula de Nicoya (Provincia de Puntarenas, Costa Rica)
[Tesis de Licenciatura]: San José, Costa Rica, Escuela Centroamericana de Geológia, Universidad de Costa Rica,
148 p.
Nishenko, S. P., 1989, Circum-Pacific seismic potential,
1989 –1999: U.S. Geological Survey Open-File Report 89-0086, 126 p.
Nur, A., and Mavko, G., 1974, Postseismic viscoelastic rebound:
Science, v. 181, p. 204–206.
Pearson, G. W., and Stuiver, M., 1986, High-precision calibration
of the radiocarbon time scale, 500 –2500 BC: Radiocarbon,
v. 28, p. 839– 862.
Pearson, G. W., Pilcher, J. R., Baillie, M. G. L., Corbett, D. M.,
and Qua, F., 1986, High-precision 14C measurement of Irish
oaks to show the natural 14C variations from AD 1840
to 5210 BC: Radiocarbon, v. 28, p. 911–934.
Pinter, N., 1988, Isostasy and eustasy on the Osa Peninsula, Costa
Rica: Unraveling the late Quaternary geologic history
through uplift and sea level change [Master’s thesis]: University Park, Pennsylvania, Pennsylvania State University,
144 p.
Pinter, N., and Gardner, T. W., 1989, Construction of a polynomial
model of sea level: Estimating paleo–sea level continuously
through time: Geology, v. 17, p. 295–298.
Pittier, E., 1959, Leyenda del Cerro de las Cruces: Bambi, v. 32,
p. 6–7.
Plafker, G., 1969, Tectonics of the March 27, 1964, Alaska earthquake: U.S. Geological Survey Professional Paper 543-I,
62 p.
Plafker, G., 1972, Alaskan earthquake of 1964 and Chilean earthquake of 1960: Implications for arc tectonics: Journal of
Geophysical Research, v. 77, p. 901–925.
Protti, J. M., 1991, Correlation between the age of the subducting
Cocos Plate and the geometry of the Wadati-Benioff zone
under Nicaragua and Costa Rica [M.S. thesis]: Santa Cruz,
California, University of California, 66 p.
Protti, J. M., 1994, The most recent large earthquakes in Costa
Rica (1990, Mw 5 7.0 and 1991, Mw 5 7.6) and threedimensional crustal and upper mantle P-wave velocity structure of central Costa Rica [Ph.D. dissert.]: Santa Cruz, California, University of California, 116 p.
Purcaru, G., and Berckhemer, H., 1978, A magnitude scale for very
large earthquakes: Tectonophysics, v. 49, p. 189–198.
Scholz, C. H., 1990, The mechanics of earthquakes and faulting:
New York, Cambridge University Press, 439 p.
Shipley, T. H., and Moore, G. F., 1986, Sediment accretion, subduction, and dewatering at the base of the slope off Costa
Rica: A seismic reflection view of the décollement: Journal
of Geophysical Research, v. 91, p. 2019–2028.
Shipley, T. H., McIntosh, K. D., Silver, E. A., and Stoffa, P. L.,
1992, Three-dimensional seismic imaging of the Costa Rica
accretionary prism: Structural diversity in a small volume of
the lower slope: Journal of Geophysical Research, v. 97,
p. 4439– 4459.
Silver, E. A., Ellis, M. J., Breen, N. A., and Shipley, T. H., 1985,
Comments on the growth of accretionary wedges: Geology,
v. 13, p. 6–9.
Snead, R. E., 1982, Coastal landforms and surface features:
Stroudsburg, Pennsylvania, Hutchinson Ross Publishing
Company.
Sprechmann, P., Kuijpers, E., Alvarado, M., Avila, M., Cordero,
S., Dı́az, J., Marin, F., Moshein, J., Pinilla, G., Sáenz, L.,
Sanchez, F., Siu, D., and Teuera, R., 1979, Estratigrafı́a de
Costa Rica: San José, Costa Rica, Escuela Centroamericana
de Geologı́a, Universidad de Costa Rica, 115 p.
Stuiver, M., and Pearson, G. W., 1986, High-precision calibration
of the radiocarbon time scale, AD 1950 –500 BC: Radiocarbon, v. 28, p. 805– 838.
Taylor, F. W., Isacks, B. L., Jouannic, C., Bloom, A. L., and
Dubois, J., 1980, Coseismic and Quaternary vertical tectonic
movements, Santo and Malekula Islands, New Hebrides island arc: Journal of Geophysical Research, v. 85,
p. 5367–5381.
Taylor, F. W., Frohlich, C., Lecolle, J., and Strecker, M., 1987,
Analysis of partially emerged corals and reef terraces in the
central Vanuatu arc: Comparison of contemporary coseismic and nonseismic with Quaternary vertical movements:
Journal of Geophysical Research, v. 92, p. 4905– 4933.
Thatcher, W., 1984, The earthquake deformation cycle at the Nankai trough, southwest Japan: Journal of Geophysical Research, v. 89, p. 3087–3101.
Thatcher, W., and Rundle, J. B., 1984, A viscoelastic coupling
model for cyclic deformation due to periodically repeated
earthquakes at subduction zones: Journal of Geophysical
Research, v. 89, p. 7631–7640.
von Huene, R., and 16 others, 1995, Morphotectonic features of
the Costa Rican Pacific margin surveyed during the Sonne
76 cruise, in Mann, P., and Kolarsky, R., eds., Geologic and
tectonic development of the Caribbean plate boundary in
southern Central America: Geological Society of America
Special Paper 295 (in press).
Wells, S. G., Bullard, T. F., Menges, C. M., Drake, P. G., Karas,
P. A., Kelson, K. I., Ritter, J. B., and Wesling, J. R., 1988,
Regional variations in tectonic geomorphology along a segmented convergent plate boundary, Pacific coast of Costa
Rica: Geomorphology, v. 1, p. 239–265.
Wood, H. O., and Neumann, F., 1931, The modified Mercalli intensity scale of 1931: Bulletin of the Seismological Society of
America, v. 21, p. 277–283.
MANUSCRIPT RECEIVED BY THE SOCIETY OCTOBER 4, 1993
REVISED MANUSCRIPT RECEIVED JULY 13, 1994
MANUSCRIPT ACCEPTED SEPTEMBER 9, 1994
Printed in U.S.A.
Geological Society of America Bulletin, April 1995
473