Earthquake Hazard and Seismic
Mitigation – Douglas Co.
Craig M. dePolo
Nevada Bureau of Mines and Geology
Major Historical Earthquakes That Have Strongly Shaken
Douglas County
Date
June 3, 1887
Dec. 20, 1932
June 25, 1933
Sept. 12, 1994
Magnitude
6.5
7.1
6.0
5.8
Nearest Comm.
Carson City
Gabbs
Wabuska
Gardnerville
Effects
Building damage, liquefaction
Surface rupture, chimney damage
Building and chimney damage
Chimney damage, foundation
cracking
1932
Cedar Mtn.
Earthquake
Modified
Mercalli
Intensity
Map
Quaternary
Faults
Major Late Quaternary Faults in Douglas County
Normal Dip-Slip Faults
Genoa fault (GF)
Eastern Carson Valley fault zone (ECVFZ)
Smith Valley fault (SVF)
Antelope Valley fault (AVF)
Eastern Antelope Valley fault zone (EAVFZ)
West Tahoe-Dollar Point fault* (WTDPF)
*The West Tahoe fault intersects the surface in California,
but dips to the west and is a threat to South Lake Tahoe.
Possible Strike-Slip Faults
Double Spring Flat fault zone (right-lateral) (DSSFZ)
Eastern Carson Valley fault zone (right-lateral oblique)
Mud Lake fault zone (left-lateral) (MLFZ)
Eastern Antelope Valley fault zone (right-lateral? oblique)
Major Late Quaternary Faults Near Douglas County
Normal Dip-Slip Faults
North Tahoe fault
Incline Village fault
Waterhouse Peak fault
Slinkard Valley fault
Northern Carson Range fault zone faults
Singatzse Range fault zone
Pine Nut Mountains fault zone
Possible Strike-Slip Faults
Wabuska lineament (left-lateral?)
Faults
Selected
to
Represent
the
Earthquake
Hazard
Faults in Douglas County – Lengths, Offsets, and Age of the Most Recent Event
Fault
Lmin1
Lmax1
Dmax2
MRE3
Reference
Genoa flt.
E. Carson V. fz.
Mud Lake fz.
Double Spr Flat fz.
Smith V. flt.
Antelope V. flt.
E. Antelope V. fz.
W. Tahoe-D.P. f.
25
18
9
17
45
23
23
50
75
26
18
30
50
30
30
60
5.5
>1.4
300-400
~520-920
Holocene?
Holocene?
~3,500
~1,350
late Quat.
~4,300
Ramell+, 1999; 2012 p.c.
dePolo and Sawyer, 2005
this report
Ramelli+, 2003
Wesnousky and Caffe, 2011
Sarmiento+, 2011
Dohrenwend, 1982
Brothers+, 2009
3.5
3.6
3.7
Earthquake Magnitude Scaling Relationships Used for
Estimating Maximum Earthquake Magnitudes
Wells and Coppersmith (1994) – All Fault Types
Length (L):
Mw = 5.08 + 1.16 log (L)
Maximum Displacement (MD):
Mw = 6.69 + 0.74 log (MD)
Wesnousky (2008) – All Fault Types
Length (L):
Mw = 5.30 + 1.02 log (L)
Faults in Douglas County – Maximum Magnitude Estimates
Fault
Lmin-wc Lmin-wy Lmax-wc Lmax-wy Dmax-wc
Genoa flt.
E. Carson V. fz.
Mud Lake fz.
Double Spr. Flat fz.
Smith V. flt.
Antelope V. flt.
E. Antelope V. fz.
W. Tahoe-D.P. f.
6.7
6.5
(6.2)
6.5
7.0
6.7
6.7
7.1
6.7
6.6
(6.3)
6.6
7.0
6.7
6.7
7.0
7.3
6.7
6.5
6.8
7.1
6.8
6.8
7.1
7.2
6.7
6.5
6.8
7.0
6.8
6.8
7.1
7.2
>6.8
7.1
7.1
7.1
Scenario Earthquakes for Faults in Douglas County
Fault
GF
ECVFZ
SVF
AVFZ
DSFFZ
MLFZ
EAVFZ
WTDPF
Earthquake
Magnitude
7.2
6.8
7.1
7.1
6.8
6.5
6.8
7.1
Type
Normal Slip
Normal Slip
Normal Slip
Normal Slip
Strike Slip
Strike Slip
Normal Slip
Normal Slip
Scenario Epicenter
Latitude Longitude
38.878°
39.037°
38.875°
38.667°
38.788°
38.863°
39.713°
39.006°
-119.753°
-119.747°
-119.337°
-119.434°
-119.608°
-119.720°
-119.513°
-119.986°
Earthquakes
in
Douglas
County
Probabilities of Earthquakes in Douglas County Based on
Occurrence Rate Analysis of Instrumentally Recorded Earthquakes from 1970-2009
Earthquake
Magnitude
≥5
≥6
≥7
Occurrence
Rate
0.091 events/y
0.013 events/y
0.002 events/y
Timeframe
50 Years
100 Years
98.9%
48%
9.5%
99.9%
73%
18%
Probabilities of Potentially Damaging Earthquakes and
Likely Damaging Earthquakes within 50 Years for Douglas County Communities
Community
GARDNERVILLE R.
GENOA
GLENBROOK
INDIAN HILLS
JOHNSON LANE
MINDEN
STATELINE
TOPAZ LAKE
Potentially
Damaging
Earthquake
Mag≥6/50km
59-62%
59-63%
59-62%
61-64%
61-64%
60-63%
57-61%
52-57%
Mag≥5/3km
14%
16%
6%
14%
12%
12%
21%
9%
Earthquakes
Likely Causing
Intensity VII
Mag≥6/20km
Mag≥7/50km
28-29%
27-28%
33-34%
34-35%
31-33%
29-30%
26-27%
26-27%
15-20%
15-20%
15-20%
15-21%
16-20%
15-20%
14-19%
14-18%
Potentially Life-Threatening Earthquake Damage
Community
GARDNERVILLE R.
GENOA
GLENBROOK
INDIAN HILLS
JOHNSON LANE
MINDEN
STATELINE
TOPAZ LAKE
All Earthquakes
Likely Causing
Intensity VII
Probability in 50 years
33-40%
36-45%
39-48%
40-49%
36-45%
32-41%
29-38%
30-38%
Probabilities of Modified Mercalli Intensity Levels Occurring in
Douglas County Communities Based on the U.S. Geological Survey Hazard Curves
Earthquake
Intensity
VI
VII
VIII
IX
50-Year
Probability
100-Year
Probability
68-78%
39-48%
11-19%
2-8%
90-95%
63-73%
21-35%
5-16%
Potential Unreinforced
Masonry Buildings
Estimated Costs of Earthquakes Occurring along the
Major Late Quaternary Faults in Douglas County – HAZUS MH Computer Modeling
Fault
E. Carson V. f
Genoa f
Double Spring F. f
Mud Lake f
W. Tahoe-D.P. f
Antelope V. f
Smith V. f
E. Antelope V. f
* NV only
Earthquake Building Transportation Utility Total
Magnitude Damage Damage
Damage Cost*
M6.8
M7.2
M6.8
M6.5
M7.1
M7.1
M7.1
M6.8
$741M
$423M
$314M
$216M
$195M
$140M
$127M
$70M
$12M
$7.6M
$7.2M
$5.7M
$4.8M
$3.5M
$5M
$2.7M
$21M
$19M
$12M
$7M
$7M
$13M
$25M
$6M
$774M
$450M
$333M
$229M
$207M
$157M
$157M
$79M
Earthquake Consequence Mitigation
• Goal 1: Adopt and Enforce Current Building
Codes and their Seismic Provisions.
• Goal 2: Assess Earthquake Vulnerabilities of
Existing Buildings and Create Strategies to
Reduce Earthquake Risks from these
Buildings.
• Goal 3: Reduce Content and Nonstructural
Hazards in Homes, Businesses, and Public
Buildings.
• Goal 4: Encourage the Purchase of
Earthquake Insurance.
• Goal 5: Provide Leadership Encouraging
Earthquake Preparedness and Mitigation
Activities at All Levels in the County.
• Goal 6: Encourage and Plan for Appropriate
Land Use to Minimize Earthquake Damage
and Losses.
• Goal 7: Plan for a Successful Earthquake
Disaster Emergency Response and Recovery.
Suggested Prioritization of Actions for Earthquake Resiliency
Rank
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
Goal & Action
G5A1/G5A2/G3A1/G4A1
G2A1
G2A2
G1A2
G2A3
G2A4
G7A1
G2A5
G5A3
G1A3
G3A3
G2A6
G7A2
G6A1
G6A2
G6A4
G6A3
G3A2
G1A1
Title
Public Awareness Campaign
Emergency facility assessment
School and county bldg. assess
Mobile home guidelines
Encour foundation anchoring
Eq risk bldg assess
Eq disast Scenario
Seis rehab tech strategy costs
Encour support comm GIDs
Site velocity eval & map
Engineering nonstructural mit
Rehab highest risk bldgs.
Eq recovery plan
Seismic hazard maps
Eq fault avoidance
Paleoseismic studies
Other eq haz mitigation
Assist w/bldg. content mitigation
Adopt IBC – in progress
Benefit
reduce eq injuries
emerg response
safety and ER
reduce eq losses
reduce eq losses
assess vulnera
motivation & vuln
decision tool
reduce eq risk
IB code tool
reduce eq risk
reduce eq risk
facilitate recov
plan reduce risk
reduce eq risk
eq hazard charac
reduce eq risk
increase eq safety
reduce eq risk
Some Conclusions
• Douglas County has a high level of earthquake hazard.
• 29% to 49% chance in 50 years for a potentially lifethreatening earthquake in Douglas County communities.
• Douglas County has prepared through good building code
adoption and enforcement, and comprehensive insurance.
• Public awareness and mitigation through leadership and
example is critical in the near time frame, as well as specific
seismic risk assessments.
• Planning is Mitigation.