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21st Century Neotectonic Fault Behaviour Observations Implications For Circum-Pacific Seismic Hazard
Gregory Paul De Pascale*,
Geologia y Centro de Excelencia en Geotermia de Los Andes (CEGA), Facultad de Ciencias Fisicas y Matematicas (FCFM),
Universidad de Chile, Plaza Ercilla 803, Santiago, Chile
*Contact email: [email protected]
Abstract. People and the infrastructure we build are
impacted not only by fault rupture and strong ground
motions during earthquakes, but also due to coseismic
geohazards (e.g. liquefaction, landslides, etc). Through
better understanding earthquakes and the faults that
generate them, we can create more resilient societies. Here
recent neotectonic observations are discussed including
recent challenges to long-standing fault behaviour models
such as the characteristic earthquake model, as well as
reliance on limited data for development of regional and
national building codes and seismic hazard models.
st
Importantly, recent 21 Century observations from Chile,
New Zealand, California, and Japan, all show that some of
the long-standing fault behaviour models are perhaps
inaccurate in the characterisation of seismic hazard.
Importantly, new evidence, oftentimes derived from high
resolution topography, demonstrate that fault behaviour is
compilicated, sometimes with full ruptures and partial
ruptures along faults with coresponding variability in
earthquake size. These observations help us revise our
view of neotectonic deformation in and around the circumPacific, including Chile, and determine potential hazards
both within the subduction zone as well as along crustal
faults while outlining some research goals for Neotectonic
st
investigations in Chile during the 21 Century.
Keywords: neotectonics, seismic hazard, Alpine Fault,
Japan, Chile, New Zealand, fault behaviour
1 Introduction – Seismic Hazard, Active
Faults and Fault Behaviour Models
Earthquakes are seismic waves generated through the
sudden release of elastic strain energy in the Earth’s crust
during rapid slip along faults. Major faults which lie at the
boundaries between tectonic plates tend to accommodate
high proportions of relative plate motions and thus have
correspondingly higher rates of stress and strain
accumulation, and higher slip-rates, than smaller faults,
which leads to large and damaging earthquakes when large
faults slip and release this stored energy. Because major
plate boundary faults, like the Alpine Fault in New
Zealand and the San Andreas in California, or the
subduction zone plate boundary in Chile accommodate
large proportions of relative plate motions, therefore
understanding the earthquake cycle along these faults is
extremely important to better characterize seismic hazards
and for the development of physical earthquake models.
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Regional catalogs of seismicity are thought to be well
described by the Gutenberg-Richter (GR) relationship: log
n = a – bM, with n being the number of events of
magnitude M and a and b are constants (Gutenberg and
Richter, 1944), however from studies of specific fault
zones (e.g. the Newport-Inglewood, Elsinore, Garlock, and
San Andreas faults in California), it appears that these
faults do not satisfy the GR relationship during a nonentire seismic cycle along these faults (Wesnousky, 1994)
and are instead in accord with the characteristic earthquake
model (CEM; Schwartz and Coppersmith, 1984). The
CEM states that during time between maximum-size
earthquakes along a fault segment or fault zone is
generally quiescent, and that these faults tend to generate
earthquakes of generally the same size (characteristic) at or
near the maximum magnitude (Schwartz and Coppersmith,
1984). In addition to the CEM, the uniform-slip models
(USM) suggests constant slip rate and frequent moderatesized events (Sieh and Jahns, 1984), and the variable slip
model (VSM) with slip at a point varying between each
major earthquake (Schwartz, 1989) are used to describe
the recurrence of earthquakes along faults and are widely
applied in seismic hazards assessments and earthquake
forecasting worldwide. Importantly, the applicability of
these models to describe the behavior of the San Andreas,
or other major faults has recently been called into question
(e.g. Zielke et al., 2010; Kagan et al., 2011, De Pascale et
al., 2014; Zielke et al., 2015). Uncertainty regarding the
applicability of these models (Figure 1) to the fault that
they were developed from raises some important questions
about our knowledge and models about the seismic cycle
and fault behaviour in general.
2 Recent 21st Century Observations and
Changing Views on Major Fault Behaviour
Prior to 2010, the characteristic earthquake model (CEM;
Schwartz and Coopersmith, 1984), and the uniform slip
model (USM; Sieh and Jahns, 1984) tended to dominate
the way researchers viewed major plate boundary faults
and earthquake hazards. In 2010, a number of researchers
including Akciz et al., Grant Ludwig et al., and Zielke et
al. came to the conclusion (using high resolution light
detection and ranging, lidar data) that perhaps the plate
boundary San Andreas Fault in California does not fit the
CEM based on new data, and instead that perhaps the fault
has bimodal character with partial ruptures and moderate
ST 2 NEOTECTÓNICA, PALEOSISMOLOGÍA Y SISMOLOGÍA
magnitudes as well as full ruptures with large surface slip.
Whereas, Zielke et al. (2012) provided compelling
evidence from the San Andreas Fault suggesting that the
fault does not conform to either the CEM or the USM and
a completely variable model, with variable slip a point
from event to event, is a possibility.
cumulative slip
a) variable slip model
Observations
on the offset distribution records from the along the Alpine
Fault (De Pascale et al., 2014), it appears that slip is
uniform at a point (Figures 1 & 2) along the central Alpine
Fault (De Pascale et al., 2014), however near the junction
with the Marlborough Fault System (MFS) at the southern
end of the northern Alpine Fault segment, the slip records
become more complex (Figure 2). However, not enough is
known about Alpine Fault slip rate variability to determine
if it is consistent with the USM or the CEM.
variable displacement per event
at a point
constant slip rate along length
variable earthquake size
distance along fault
b) uniform slip model
cumulative slip
constant displacement per event
at a point
constat slip rate along length
constant size large earthquakes:
more frequent moderate earthquakes
distance along fault
c) characteristic earthquake model
cumulative slip
constant displacement per event
at a point
variable slip rate along length
constant size large earthquakes:
infrequent moderate earthquakes
distance along fault
Figure 1. Models of fault behavior: a) variable slip model after
Schwartz (1989), b) uniform slip model after Sieh and Jahns
(1984), c) after Schwartz and Coppersmith (1984), all compiled
by Berryman and Beanland (1991).
In 2011, Kagan et al. suggested terms such as the
“earthquake cycle” and “characteristic earthquake” are
“buzz phrases” that do not withstand statistical testing.
Specifically, these authors (Kagan et al., 2011) cite the
plate boundary 2004 Sumatra and the 2011 Tohoku
earthquakes where ruptures propagated through supposed
segment boundaries, and therefore had higher moment
release than if these earthquakes stopped as supposed
boundaries as expected (Table 1). Additionally, Jackson
and Kagan (2011) point out that the 2010 Maule
Earthquake in Chile ruptured well beyond preassigned
segement bounderies (and supposed locations where
ruptures would terminate). Perhaps we are learning new
behaviour, or perhaps there are limitations in our data that
contributes to the development of these models and our
understanding of faults? Looking at New Zealand’s Alpine
Fault in this light is instructive. Based on recent research
that focused on lidar and field mapping and documenting
previous surface ruptures (e.g. De Pascale, 2014; De
Pascale et al., 2014), it seems likely that either the Alpine
Fault has bimodal behavior with large through-going
surface ruptures in addition to moderate (although
landscape-altering) earthquakes; and/or that there are other
seismic sources that are reflected in the off-fault (hitherto
assumed Alpine Fault) records based a combined analysis
of both surface ruptures measurements with distributions
and timing of earthquakes along the Alpine Fault. Based
Figure 2. The tectonic setting of New Zealand showing
bathymetry and topography of New Zealand, the Alpine Fault (in
red) connecting two plate-boundary subduction zones, and the
Zealandia Continent that is 90% submarine (background image
compiled by NIWA, New Zealand). Note that Alpine Fault
rupture behaviour is less regular where deformation is partitioned
onto several structures at the northern end of the Alpine Fault
near the Marlborough Fault Zone (MFS).
Prior to the 21st Century aforementioned studies along the
San Andreas and Alpine Faults, both were assumed to
exhibit characteristic behaviour and these recent
observations provide evidence that 21st century techniques
(such as lidar analysis), better model and document recent
tectonic deformation than via previous methods (e.g.
airphoto mapping, etc). Importantly, in a review of lidar
studies on fast-slipping faults worldwide, Zeilke et al.
(2015) note slip accumulation and release along fault
segments are dominated by repetition of large, and almost
constant increments of offsets, although importantly the
timing of these ruptures is oftentimes irregular.
3 Discussion and Implications of Recent
Observations on Chilean Neotectonics
Because a number of 21st century great earthquakes
demonstrate that these fault segments do not always
terminate ruptures (e.g. 2010 Maule earthquake in Chile,
2004 Sumatra earthquake, and the 2011 Tohoku
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AT 1 GeoloGía ReGional y Geodinámica andina
earthquake in Japan), then should we still consider
segments relevant? What are the implications for Chile?
New evidence from recent studies along major faults show
that the CEM is perhaps unsuitable for the determination
of seismic hazard. Table 1 shows the expected length of
surface ruptures and magnitudes with actual and
corresponding difference is moment magnitudes that
occured during these events and demonstrates that recent
assumptions about fault behaviour have been incorrect and
the effects and hazard have therefore been underestimated
with high consequences. Two areas here in Chile deserve
further attention, incluing unequivocally Quaternary active
crustal faults (e.g. San Ramon fault in Santiago, and the
LOFZ in Central to Southern Chile) and the main plate
boundary subduction zone. Simply put, most of the crustal
faults in Chile do not have historic records, primarily due
to the faults having longer recurrence intervals than written
records and secondly due to sparsely populated areas that
are difficult to attribute shaking to any specific seismic
source (i.e. De Pascale et al., 2014). However, there is
ample evidence that demonstrates that the LOFZ (e.g.
Cembrano et al., 1996; Vargas et al., 2013) and San
Ramon Faults (e.g. Vargas et al., 2014) are indeed active
structures with associated seismic hazard. Are the current
estimates (Table 1) representitive of the actual hazard? Do
we have enough data here to evaluate the hazard or are
these underestimations? Finally a consideration of the plate
boundary in Chile which of course was the source of the
largest historic earthquake on Earth, the 1960, magnitude
9.5 Valdivia earthquake. Is this the maximum size
expected for the Chilean plate boundary? Recent research
and modelling by Kagan and Jackson (2013) suggest that
a) all major subduction zones are capable of magnitude 9
earthquakes and that magnitude 10 earthquakes cannot be
considered impossible with global recurrence times from a
few hundred or thousand years. The natural laboratory of
Chile holds the answers to some of the above questions
that can be pursued with geological, geophysical, and
seismological techniques. Time of course, with additional
accumulation of knowledge (and of course additional
observations from future events) will continue to increase
our understanding of tectonic deformation and help us
better prepare for future earthquakes in the 21st Century.
Acknowledgements
Thanks to FCFM for Universidad de Chile’s (UChile)
Academic start-up fund, and CEGA FONDAP CONICYT
15090013 for support and to New Zealand’s (NZ)
Earthquake Comission (EQC), Geological Society
(GSNZ), Education NZ, and University of Canterbury for
supporting my PhD research.
References
Berryman, K.; and Beanland, S. 1991. Variation in fault behaviour in
different tectonic provinces of New Zealand. Journal of Structural
Geology 13: 177–189.
265
Cembrano, J.; Hervé, F.; Lavenu, A. 1996. The Liquine-Ofqui fault
zone: a long-lived intra-arc fault system in southern Chile.
Tectonophysics 259: 55-66.
De Pascale, G.P. 2014. Neotectonics and Paleoseismology of the
Central Alpine Fault, New Zealand. Ph.D. Thesis (unpublished),
University of Canterbury, 238 p.
De Pascale, G.P.; Davies, T.R.; Quigley, M.C. 2014. Lidar reveals
uniform Alpine Fault offsets and bimodal plate boundary
rupture behavior, New Zealand. Geology 42 (5): 411-414.
Gutenberg, R.; and Richter, C.F. 1944. Frequency of earthquakes in
California. Bulletin of the Seismological Society of America 34:
185- 188.
Kagan, Y.Y.; Jackson, D.D.; and Geller, R.J. 2011. Characteristic
earthquake model, 1884-2011: R.I.P. Seismological Research
Letters 83(6): 951-953.
Kagan, Y.Y.; and Jackson, D.D. 2013. Tohoku Earthquake: A
Surprise? Bulletin of the Seismological Society of America 103
(2B): 1181–1194.
Nishenko, S. P. 1991. Circum-Pacific seismic potential – 1989–
1999. Pure and Applied Geophysics 135: 169–259.
Schwartz, D.P. 1989. Paleoseismicity, persistence of segments, and
temporal clustering of large earthquakes - examples from the San
Andreas, Wastach, and Lost River fault zones. U.S. Geol. Surv.
Open-file Report 89 (315): 361-375.
Schwartz, D.; and Coppersmith, K. 1984. Fault behavior and
characteristic earthquakes: Examples from the Wasatch and San
Andreas fault zones. Journal of Geophysical Research 89 (B7).
Sieh, K.E.; and Jahns, R.H. 1984. Holocene activity of the San
Andreas fault at Wallace Creek, California. Geological Society of
America Bulletin 95: 883-896.
Wesnousky, S.G. 1994. The Gutenburg-Richter or characteristic
earthquake distribution, which is it?. Bulletin of the
Seismological Society of America 84 (6): 1940-1959.
Vargas, G.; Rebolledo S.; Sepúlveda S.; Lahsen, A.; Thiele R.;
Townley B.; Padilla C.; Rauld R.; Herrera M.; Lara, M.; 2013.
Submarine earthquake rupture, active faulting and volcanism
along the major Liquiñe- Ofqui Fault Zone and implications for
seismic hazard assessment in the Patagonian Andes. Andean
Geology 40 (1): 141 -171.
Vargas, G.; Klinger, Y.; Rockwell, T.K.; Forman, S.L.; Rebolledo, S.;
Baize, S.; Lacassin, R.; and Armijo, R. 2014. Probing large
intraplate earthquakes at the west flank of the Andes, Geology 42
(12): 1083-1086.
Zielke, O.; Arrowsmith, J.R.; Grant Ludwig, L.; Akcsz, S.O. 2010.
Slip in the 1857 and earlier large earthquakes along the Carrizo
Plain, San Andreas Fault. Science 327: 1119-1122.
Zielke, O.; Arrowsmith, J.R.; Grant Ludwig, L.; and Akciz, S.O.
2012. High resolution topography-derived offsets along the 1857
Fort Tejon earthquake rupture trace, San Andreas Fault. Bulletin
of the Seismological Society of America 102 (3): 1135–
1154.
Zielke, O.; Klinger, Y.; and Arrowsmith, J.R. 2015. Fault slip and
earthquake recurrence along strike-slip faults — Contributions of
high-resolution geomorphic data. Tectonophysics 638: 43-62.
ST 2 NEOTECTÓNICA, PALEOSISMOLOGÍA Y SISMOLOGÍA
Table 1. Three major 21st Century earthquakes (2004 Indian Ocean, 2010 Maule Chile, and 2011 Tohoku Japan) where the expected
fault displacements, rupture lengths, and magnitudes were all underestimated prior to the event due to ruptures continuing past supposed
fault rupture/segement boundaries. Therefore the earthquakes were much larger with higher consequences than expected. Note that the
studies listed in the second section below (along faults without historic records of rupture, i.e. New Zealand’s Alpine Fault, and Chile’s
Liquiñe-Ofqui fault zone (LOFZ), and San Ramon Fault) have a number of uncertainties (or data gaps), and based on the examples listed
here may be underestimating effect (and thus seismic hazard). Note that n.a. is not applicable and n.d. is not determined.
Historical
Earthquake
Year
Expected
Rupture
Length
(km)
Rupture
Length
(km)
Average and/or
maximum slip
(m)
Expected
Magnitude
(Mw)
Observed
Magnitude
(Mw)
References
(not always the
studies that predicted
outcomes)
<8
9.1 to 9.3
Kagan et al. 2011;
Indian Ocean,
Sumatra
2004
<250
1,500
7 average and and
20 max
(observed)
Maule, Chile
2010
~100
700
10 average
(observed)
7.5
8.8
Nishenko, 1991
Kagan et al., 2011
Tohoku, Japan
2011
n.d.
300
40 max
(observed)
7.7 to 8.35
9.1
Kagan and Jackson,
2013
~8.1
?
De Pascale et al.,
2014
Future Events
on Faults
Without
Historic
Ruptures
~7.5 m average
(derived from
field
measurements)
Alpine Fault,
New Zealand
n.a.
>300
?
LOFZ, Chile
n.a.
?
?
?
7.1
?
Vargas et al., 2013
San Ramon
Fault, Chile
n.a.
15-35
?
5 m average
(expected)
~7.5
?
Vargas et al., 2014
!
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