Earthquake Occurrence in the Reno-Carson City Urban Corridor
Craig M. dePolo
Nevada Bureau of Mines and Geology
John G. Anderson
University of Nevada, Reno
Department of Geological
Diane M. dePolo
University of Nevada, Reno
Jonathan G. Price
Nevada Bureau of Mines and Geology
published in the
Seismological Research Letters,
Volume 68, May/June, 1997, pages 401-412.
The Reno-Carson City urban corridor is the second most populated region
in Nevada, and lies in one of the most seismically active parts of the
State. This has prompted the development of an earthquake scenario (dePolo
et al., 1996) to assist with earthquake preparedness and emergency response
planning within the corridor's communities. As part of this effort, we
have estimated probabilities of a potentially damaging earthquake affecting
the scenario area (Figure 1) over a 50-year time period. This paper briefly
describes local historical earthquakes of magnitude >=6 and compares their
occurrence rates with b-value curve extrapolations from the instrumental
time period and preliminary estimates based on local fault activity rates.
Figure 1: Major historical earthquakes in the Reno-Carson
City urban corridor (population ~400,000), western Nevada, based on published
and ongoing research. All earthquake locations, except the 1966 and the
1994 earthquakes, are only approximately known. Magnitudes used are from
Rogers et al. (1991).
(Click on image for a high-resolution Adobe
Acrobat PDF file.)
Thirteen earthquakes of magnitude 6 or greater have occurred in the scenario
region since 1850 (see Figure 1 and Table 1). These
events are briefly described in the Appendix. For
many of the earlier events, only newspaper accounts are available and the
locations are uncertain. Two of the earliest events on record in western
Nevada (1852? and 1857) are not shown on Figure 1 because their locations
are highly uncertain at this time. Although their location within the scenario
area is equivocal, these two events did appear to occur in western Nevada
(see Appendix for discussion). Further research,
including a review of local diaries, is planned for these and other, earlier
events to aid in understanding their locations and sizes.
Figure 2: Time line of major earthquakes in western Nevada.
Magnitudes are from Rogers et al. (1991) and the University of California,
(Click on image for a high-resolution Adobe
Acrobat PDF file.)
Earthquake magnitudes used in this paper are from Rogers and others
(1991) and from the University of California, Berkeley. Many of these magnitudes
are uncertain and other magnitudes are reported (see Appendix).
Variations in magnitude estimates are larger for the earlier events (0.2
to 0.7 magnitude units), whereas events within the last few decades have
been determined within about 0.1 magnitude unit.
A time line of the larger earthquakes occurring in the scenario area
(see Figure 2) clearly shows that the mid to late 1800s was the most active
period in the area's history. No earthquakes of magnitude >=6.5 have occurred
in the scenario area since 1869, but earthquakes with magnitudes 6 to 6.4
have continued, with intervals between earthquakes ranging from 65 days
to 28 years.
The 1868-1869 sequence and the 1914 earthquakes were both temporally
clustered, although the 1914 earthquakes were apparently spatially separated.
Although of smaller magnitudes, the 1868-1869 sequence bears resemblance
to the famous 1954 Rainbow Mountain-Stillwater-Fairview Peak-Dixie Valley
earthquakes east of the scenario area, which included two magnitude 6 earthquakes
and three events of magnitude 6.8 or larger (the largest was magnitude
7.2) over a time period of six months (Slemmons, 1957). This temporal clustering
of earthquakes has an important risk implication. Buildings weakened by
the initial event may suffer further damage or collapse from subsequent
events, as occurred in Fallon in 1954 from the July 6 and August 23 earthquakes
(Steinbrugge and Moran, 1956).
Figure 3: Seismicity in western Nevada from 1960 to 1995.
Data are from the University of Nevada, Reno Seismological Laboratory.
(Click on image for a high-resolution Adobe
Acrobat PDF file.)
Probabilistic Estimates of Earthquake Activity
The probability of a magnitude >=6 earthquake occurring in the scenario
area is estimated from historical earthquakes, instrumental seismicity,
and geological estimates. We use two methods to estimate rates of magnitude
>=6 earthquakes, three methods for magnitude >=6.6 earthquakes, and four
methods for magnitude >=7 earthquakes (Table 2).
The historical earthquake method simply counts the number of earthquakes
of a given magnitude or larger within a region. The historical time period
is then divided by the number of events to get the average recurrence interval.
The inverse of this average recurrence interval is the earthquake occurrence
rate (number of a given magnitude event or larger per year). The probability
of an earthquake in T years is estimated using (in Fortran notation):
p = 1 - exp(-N*T),
where p is the probability of one or more events occurring of
a given magnitude or larger, N is the number of events per year,
and T is the time period of interest (in this case, we use 50 years).
This equation assumes earthquake occurrence can be described by a Poisson
process, hence, earthquakes are considered to occur randomly through time.
Considering uncertainties in magnitudes and locations of historical earthquakes,
there were 9 to 12 events in 145 years (~1851 to 1995) with magnitudes
of 6 or larger, 1 to 3 events of magnitude 6.6 or larger, and 1 to 2 events
of magnitude 7 or larger that have occurred within the scenario boundaries.
The instrumental seismicity method uses earthquakes recorded in the
scenario area between 1960 and 1995. This 36-year period roughly represents
the installation of local instrumention and, consequentially, a relatively
complete earthquake catalog. The number of events per year of a given magnitude
or larger are modeled by the standard Gutenberg-Richter b-value formula
(Gutenberg and Richter, 1954; here in Fortran notation):
N = 10**(a - b*M),
where N is the number of events per year with magnitude M
or larger, a is the productivity (an overall earthquake activity
coefficient), and b is a coefficient that describes the relative
number of small earthquakes versus large earthquakes (the slope of the
relationship). These coefficients are determined by fitting a line through
the instrumentally recorded occurrence rates. These rates are derived after
testing the completeness of different magnitude bins (±0.5 magnitude
units wide) centered on even magnitude values by using techniques after
Stepp (1972). The instrumental seismicity from the University of Nevada,
Reno Seismological Laboratory catalog includes 5773 events (Figure 3) and
confirms the active seismicity of the area. The seismicity within the scenario
boundaries and a band 5 km wide outside of the boundaries are used to derive
the b-value line shown in Figure 4. The b-value formula is then used to
extrapolate to magnitude >=6, magnitude >=6.6, and magnitude >=7 occurrence
rates to give the instrumental seismicity rate estimates (Table
2). To evaluate the potential uncertainty in the instrumental method,
we removed the 1994 Double Spring Flat earthquake and its associated earthquake
sequence by limiting the time frame to events occurring prior to 1994.
Occurrence rates were significantly affected, with the largest difference
being about a factor of 2. We thus assumed that the uncertainty in the
instrumental method could be represented by varying the occurrence rate
by a factor of ±2, which corresponds to a variation of ±0.3
in the a coefficient (Figure 4).
Figure 4: Average number of events per year, including aftershocks,
for the years 1960 through 1995, in the western Nevada scenario area (octagons).
The crosses are these activity rates multiplied by ±2 to represent
uncertainty. The b-value curve is determined from a visual fit to the points
shown in the plot. N is the number of events with magnitude M or larger.
The dashed lines represent the estimated uncertainty of the relationship
using ±0.3 times the a value.
(Click on image for a high-resolution Adobe
Acrobat PDF file.)
The b-value derived here (b=0.8) is also used in the "modified historical"
method to extrapolate from the historical rate of 9 to 12 events with magnitude
>=6 to estimate the number events with magnitude >=7. This provides an
independent estimate of large earthquake rates, since the magnitudes of
the early events are uncertain.
The geological method uses the local Quaternary or suspected Quaternary
faults that are either partly, or entirely, within the scenario area. Expected
earthquake magnitudes (mean-value magnitudes) are estimated using speculative
earthquake segment lengths and maximum surface displacements from faults.
These parameters are then used in empirically derived formulas to estimate
surface-wave magnitude. The empirical relations used include Basin and
Range province data (dePolo et al., 1990) and data from extensional environments
(Mason, 1992, 1996). These regressions are for all senses of displacement
(Table 3). The average of all values characterized
for a fault are used for the expected magnitude. In most cases, this is
limited to segment length because maximum surface displacements have not
been reported or measured. Although detailed segmentation studies have
in general not been conducted for these faults, the defined segment lengths
are comparable to historical Basin and Range province ground-rupturing
events. Further, the logarithmic scale of length used in magnitude versus
length relations makes size estimates relatively insensitive to moderate
errors in length estimates. Earthquake size estimates based on length are
assumed to be accurate to within ±0.3 magnitude units. Since most
earthquakes of magnitude 6 to 6.5 in the Great Basin are not associated
with significant primary surface rupture (dePolo, 1994), the minimum magnitude
associated with faults having surface expression is magnitude 6.6. Fault
slip rates were estimated using reported rates, offset Quaternary surfaces,
geologic offsets, or based on a fault's geomorphic expression (dePolo,
in prep.). A paleoseismic surface displacement or a displacement empirically
correlated with the expected earthquake magnitude is divided by maximum
and minimum fault slip rates to get the minimum and maximum average earthquake
recurrence intervals. Displacements correlated with magnitude are maximum
surface values and are halved to represent average displacement for the
calculation of the average earthquake recurrence interval. Thus, each fault
is associated with an earthquake magnitude and an average earthquake recurrence
interval, or occurrence rate. Occurrence rates for faults associated with
Figure 5: Principal Quaternary and suspected Quaternary
faults in western Nevada. Faults are shown schematically, with balls on
the downthrown side and arrows indicating strike-slip motion. The lines
with dots are seismogenic lineaments. Fault acronyms correspond to Table
(Click on image for a high-resolution Adobe
Acrobat PDF file.)
a given magnitude or larger are added together for use in determining
the probabilities of earthquake occurrence.
The 30 faults considered in this study (Table 4
and Figure 5) include only the larger or more prominent Quaternary and
suspected Quaternary faults. It is likely that there are more faults in
the scenario area yet to be identified. Also included in this data set
are two "seismogenic lineaments". These are structural trends that have
discontinuous Quaternary fault scarps and/or associated seismicity. The
importance of these lineaments is underscored by the location of two magnitude
6 earthquakes that occurred in 1948 (Verdi earthquake) and in 1966 (Boca
Valley earthquake) along or proximal to the Dog Valley lineament, which
lies immediately west of the scenario area. Although fault scarps and seismicity
indicate these lineaments are seismogenic, they lack the through-going
character of the other identified faults. Consequentially, the weak and
discontinuous geomorphic expressions are assumed to indicate a limit to
their potential earthquake magnitudes. For example, they are considered
unlikely to rupture over their entire lengths during single events.
The earthquake occurrence rates estimated using the different methods
are presented in three magnitude groups, magnitude >=6, >=6.6, >=7 (Table
2), which were chosen for the following reasons. A magnitude 6 earthquake
is a large enough event to be expected to cause damage over part of the
scenario area. A magnitude of 6.6 is based on the minimum magnitude value
associated with primary tectonic surface faulting, and hence, the minimum
magnitude value assigned to faults having surface expression. An event
of this size could cause damage over much of the scenario area, with locally
severe damage. A magnitude 7 or larger earthquake would be expected to
cause severe damage over large portions of the urban area (dePolo et al.,
A clear observation from Figure 2 and the differences in the historical
and instrumental methods (Table 2) is that the past
36 years have been seismically quiet relative to the first 100 years of
the region's history. This good fortune cannot be relied upon to continue.
However, although a longer time interval is considered to give a more reliable
estimate of seismicity rates, the possibility that the first 100 years
of our historical record were unusually active cannot be ruled out. This
is supported by the geologic estimates, which are similar to the lower
instrumental rates, but the geological estimates must be considered to
have very large uncertainties at this time, both in fault identification
and in earthquake occurrence rate estimation. More Quaternary faults are
suspected to exist, some within ranges and others buried by recent alluvium
within basins. Further, the estimated slip rates generally only consider
faults with normal slip, although suspicious lineaments and a predominance
of strike-slip focal mechanisms from local earthquakes (Martinelli, 1989)
indicate unrecognized strike-slip faulting. Thus, we suspect that future
research will tend to increase these rates and, consequently, to increase
the geologic probability estimates of having an earthquake. Other assumptions
that potentially underestimate the geologic probability are the size of
the maximum background earthquake and the percentage of maximum surface
displacement that represents the average displacement. If a smaller maximum
background earthquake is assumed, smaller sized events that occur more
frequently would be estimated for some faults. If average displacement
is a smaller percentage of maximum displacement, earthquake occurrence
would also increase. In this light, the similarity of geological rates
and instrumental rates may be coincidental, with a longer term average
somewhere between the instrumental and historical estimates.
As mentioned earlier, several earthquakes in the Great Basin have occurred
as sequences of strong earthquakes, rather than as individual events. If
the communities within the scenario area face multiple magnitude >=6 earthquakes
over a short time period, serious mitigation efforts and prudent engineering
and construction practices will likely have more than a one-time benefit.
The probabilities estimated for having earthquakes in the scenario area
over a 50-year period are summarized in Table 5.
The probability of at least one magnitude >=6 event is estimated to be
between 34% and 98%, the probability of a magnitude >=6.6 event between
9% and 64%, and the probability of a magnitude >=7 event between 4% and
50%. Daily probabilities are estimated to range from 0.02% to 0.0002% (Table
5), with the uncertainty in each magnitude category varying by an order
of magnitude. The scenario area could also be affected by earthquakes that
are nearby but outside of its boundaries, as in 1966, further raising the
total estimated hazard. Overall, the probabilities of potentially damaging
earthquakes within the region are relatively high and are commensurate
with many parts of California, a state with a well-recognized high earthquake
hazard. Thus, the earthquake hazard and potential in the Reno-Carson City
urban corridor should be considered high, and earthquake risk preparedness,
planning, and mitigation efforts are well warranted.
This paper benefitted significantly from the review and comments of Alan
Ramelli, Diane Doser, John Ebel and Dick Meewig. A special thanks goes
to Kris Pizarro of the Nevada Bureau of Mines and Geology for drafting
the figures. The Western Nevada Earthquake Scenario Project was jointly
funded by the Nevada Bureau of Mines and Geology and a grant from Federal
Emergency Management Agency to the Nevada Office of Emergency Support.
Data used in this paper were developed with support from the U.S. Geological
Survey National Earathquake Hazard Reduction Program; specifically award
#1434-95-G-2612 to the Nevada Bureau of Mines and Geology and awards #1434-94-G-2479
and #1434-95-A-01298 to the University of Nevada, Reno Seismological Laboratory.
The views and conclusions contained in this document are those of the authors
and should not be interpreted as necessarily representing the official
policies, either expressed or implied, of the U.S. Government.
Anderson, L.W. and Hawkins, F.F., 1984, Recurrent Holocene strike-slip
faulting, Pyramid Lake fault zone, western Nevada, Geology 12,
Bell, E.J., Broadbent, R. and Szumigala, A, 1982, Effects of the December
29, 1948, earthquake, University of Nevada, Reno, 15 pp. (unpublished manuscript).
Bolt, B.A. and Miller, R.D., 1975, Catalogue of earthquakes in northern
California and adjoining areas, 1 January 1910 - 31 December 1972, University
of California, Berkeley, Seismographic Station, 567 pp.
dePolo, C.M., 1994, The maximum background earthquake for the Basin and
Range province, western North America, Bull. Seis. Soc. Am. 84,
dePolo, C.M., in prep., A method using geomorphic observations to estimate
slip rates for normal faults in the Great Basin, University of Nevada,
Reno doctoral studies.
dePolo, C.M., Bell, J.W. and Ramelli, A.R., 1990, Estimating earthquake
sizes in the Basin and Range province, western North America: Perspectives
gained from historical earthquakes, in Proceedings from high
level radioactive waste management, American Nuclear Society 1,
dePolo, C.M., Rigby, J.G., Johnson, G.L., Jacobson, S.L., Anderson, J.G.
and Wythes, T.J., 1996, Planning scenario for a major earthquake in western
Nevada, Nevada Bureau of Mines and Geology Special Publication 20, 128
dePolo, D., Smith, K., Anooshehpoor, dePolo, C. and Priestley, K., 1995,
Double Spring Flat Earthquake, western Nevada, 12 September 1994, American
Geophysical Union, 1994 Fall Meeting abstracts, in 1995 Spring Meeting
proceedings, supplement to EOS, S301.
Greensfelder, R., 1968, Aftershocks of the Truckee, California, earthquake
of September 12, 1966, Bull. Seis. Soc. Am. 58, 1607-1620.
Gutenberg, B. and Richter, C.F., 1954, Seismicity of the earth and associated
phenomena, Princeton University Press, Princeton, New Jersey, 310 pp.
Holden, E.S., 1898, A catalogue of earthquakes on the Pacific Coast 1769
to 1897, Smithsonian Miscellaneous Collections, No. 1087, 253 pp.
Kachadoorian, R., Yerkes, R.F. and Waananen, A.O., 1967, Effects of the
Truckee, California, earthquake of September 12, 1966, U.S. Geol. Sur.,
Circular 537, 14 pp.
Martinelli, D.M., 1989, Geophysical investigations of the northern Sierra
Nevada- Basin and Range boundary, west-central Nevada and east-central
California, University of Nevada, Reno, Masters Thesis, 172 pp.
Mason, D.B., 1992, Earthquake magnitude potential of active faults in the
intermountain seismic belt from surface parameter scaling, University of
Utah, Masters Thesis, 110 pp.
Mason, D.B., 1996, Earthquake magnitude potential of the intermountain
seismic belt, USA, from surface-parameter scaling of late Quaternary faults,
Bull. Seism. Soc. Am. 86, 1487-1506.
Priestley, K, 1981, unpublished technical discussion on earthquakes in
the Reno area 1914 through 1960, 30 pp.
Ramelli, A.R., 1994, The 1994 Double Spring Flat earthquake, Nevada
Geology no. 25, 2-4.
Rogers, A.M., Harmsen, S.C., Corbett, E.J., Priestley, K. and dePolo, D.,
1991, The seismicity of Nevada and some adjacent parts of the Great Basin,
in Slemmons, D.B., Engdahl, E.R., Zoback, M.D. and Blackwell, D.D.,
eds., Neotectonics of North America, Geological Society of America,
Decade Map Volume, 153-184.
Ryall, A.R., 1977, Earthquake hazard in the Nevada region, Bull. Seis.
Soc. Am. 67, 517-532.
Sanders, C.O. and Slemmons, D.B., 1979, Recent movements in the central
Sierra Nevada - Walker Lane region of California - Nevada: part III, the
Olinghouse fault zone: Tectonophysics 52, 585-597.
Slemmons, D.B., 1957, Geological effects of the Dixie Valley-Fairview Peak,
Nevada, earthquakes of December 16, 1954, Bull. Seis. Soc. Am. 47,
Slemmons, D.B., 1969, Surface faulting from the December 26, 1869 Olinghouse,
Nevada earthquake, Seismological Society of America Annual Meeting, 23.
Slemmons, D.B., Jones, A.E. and Gimlett, J.I., 1965, Catalog of Nevada
earthquakes, 1852-1960, Bull. Seis. Soc. Am. 55, 537-583.
Steinbrugge, K.V. and Moran, D.F., 1956, Damage caused by the earthquakes
of July 6 and August 23, 1954, Bull. Seis. Soc. Am. 46, 15-33.
Stepp, J.C., 1972, Analysis of completeness of the earthquake sample in
the Puget Sound area and its effect on statistical estimates of earthquake
hazard, International Conference on Microzonation, Proceedings 2,
Toppozada, T.R., Real, C.R. and Parke, D.L., 1981, Preparation of isoseismal
maps and summaries of reported effects for pre-1900 California earthquakes,
California Division of Mines and Geology OpenFile Report 8111SAC, 182 pp.
Table 1 Earthquakes of Magnitude 6 and Larger
in the Scenario Region
Date Magnitude1 Location
1852? 7.3 Western Nevada
Sept. 3, 1857 6.2 Western Nevada
March 15, 1860 7.0 Pyramid Lake area
May 29, 1868 6.0 Virginia Range
Dec. 26, 1869 6.7 Virginia Range
Dec. 27, 1869 6.1 southern Virginia Range
June 3, 1887 6.3 Carson Valley
Feb. 14, 1914 6.0 Verdi area
Apr. 24, 1914 6.4 northern Virginia Range
June 25, 1933 6.0 northern Singatze Range
Dec. 29, 1948 6.0 Verdi area
Sept. 12, 1966 6.0 Truckee, CA2
Sept. 12, 1994 6.0 Double Spring Flat
1. Magnitudes from Rogers et al. (1991) and the University of California,
Berkeley for the 1994 event.
2. Outside boundary of scenario area.
Table 2 Estimated Probabilities of Earthquakes
within the Scenario Area
Interval Rate Number Probability1
Mag. Method (Years) (Events/Year) per Century in 50 Years
>=6 Historical 145 0.062-0.083 6.2-8.3 95%-98%
>=6 Instrumental >=6 0.0083-0.033 0.8-3.3 34%-81%
>=6.6 Historical 145 0.0069-0.021 0.7-2.1 29%-64%
>=6.6 Instrumental >=6 0.0028-0.011 0.3-1.1 13%-42%
>=6.6 Geological 103-106 0.0018-0.011 0.2-1.1 9%-42%
>=7 Historical 145 0.0069-0.014 0.7-1.4 29%-50%
>=7 Md. Historical 145 0.0098-0.013 1.0-1.3 39%-48%
>=7 Instrumental >=6 0.0013-0.0052 0.1-0.5 6%-23%
>=7 Geological 103-106 0.00091-0.0041 0.1-0.4 4%-19%
1. Probability of at least one event of the indicated magnitude or greater.
Table 3 Empirical Magnitude versus Fault Parameter
Magnitude versus fault length
Ms = 5.2 + 1.2 (log L) dePolo et al. (1990)
Magnitude versus maximum surface displacement
Ms = 5.27 + 1.06 (log L) Mason (1992)
Ms = 6.8 + 0.8 (log D) dePolo et al. (1990)
Magnitude versus fault length times maximum surface displacement
Ms = 6.85 + 0.58 (log D) Mason (1992)
Ms = 5.88 + 0.57 (log LD) Mason (1996)
Maximum surface displacement versus magnitude
Log D = 0.97 (Ms) - 6.5 dePolo (unpublished)
Ms = surface-wave magnitude
L = surface fault length
D = maximum surface displacement
Table 4 Major Quaternary or Suspected Quaternary
Faults in the Scenario Area
Fault Occurrence Rate
Earthquake Slip Rate Minimum-Maximum
Fault Name Acronym Magnitude1 (m/kyr)* (Events/Year) x 10-5*
Carson City flt. ccf 6.8 0.05-0.3 8-48
Carson lineament cl 6.9 0.005-0.05 0.64-6.4
Comstock flt. zn. cfz 6.6 0.005-0.05 1-13
Double Spring Flat flt. zn. dsffz 6.7 0.01-0.1 2-20
East Tahoe flt. etf 7.0 0.1-0.5 10-51
Eastern Carson Valley flt. zn. ecvfz 6.7 0.05-0.3 4.1-61
Eastern Prison Hill flt. zn. ephfz 6.6 0.05-0.3 13-74
Eastern Reno Basin flt. zn. erbfz 6.9 0.01-0.1 1.3-13
Freds Mountain flt. zn. fmfz 7.0 0.05-0.2 5.1-21
Genoa flt. zn. gfz 7.4 0.3-2.5 6.3-63
Granite Hills flt. ghf 6.6 0.05-0.3 13-74
Hungry Valley flt. hvf 6.6 0.001-0.1 0.25-25
Incline Village flt. zn. ivfz 6.6 0.01-0.1 2.5-60
Little Valley flt. zn. lvfz 6.9 0.05-0.3 6.4-39
Mount Rose flt. zn. mrfz 7.1 0.1-0.5 8.2-41
North Tahoe flt. ntf 7.0 0.05-1 3.3-10
Northern Virginia Range flt. nvrf 6.6 0.01-0.1 2.5-25
Northwest Reno fault zone nrfz 6.6 0.01-0.08 2.5-20
Olinghouse flt. zn. ofz 7.1 0.05-0.3 4.1-25
Peavine Mountain flt. zn. pmtfz 7.0 0.05-0.3 2.1-74
Peterson Mountain flt. zn. pmfz 7.0 0.05-0.3 5.1-31
Pine Nut Valley flt. zn. pnvfz 6.8 0.01-0.1 1.6-16
Pyramid Lake flt. zn. plfz 7.3 0.4-1.1 42-56
Smith Valley flt. zn. svfz 7.2 0.12-0.81 7.9-53
Spanish Springs Peak flt. zn. sspfz 6.6 0.05-0.3 13-74
Spanish Springs Valley flt. zn. ssvfz 6.9 0.05-0.3 6.4-39
Stead flt. zn. sfz 6.6 0.01-0.1 2.5-25
Wabuska lineament wl 6.9 0.01-0.1 1.3-13
Western Lemmon Valley flt. zn. wlvfz 6.6 0.01-0.1 2.5-25
Western Warm Springs Valley flt. wwsvf 6.9 0.005-0.1 0.64-13
1. Estimated values are thought to be representative of these faults, but
they are not, in general, the results of detailed studies and should not
be used for engineering studies without review. Estimated magnitude values
have a general uncertainty of ±0.3 magnitude units.
Table 5 Summary of Probabilities of Earthquakes
in the Western Nevada Scenario Area1
Number Probability2 Probability2
Mag. per Century in 50 Years in one day
>=6 0.8-8.3 34%-98% 0.003%-0.02%
>=6.6 0.2-2.1 9%-64% 0.0005%-0.006%
>=7 0.1-1.3 4%-50% 0.0002%-0.004%
1. Note that the area can also be affected by damaging motion from earthquakes
outside its borders that are not included in these estimates. Thus, these
values represent minimum probabilities of damaging earthquakes.
2. Probability of at least one event of the indicated magnitude or
Appendix - Major Earthquakes in the Western Nevada
Magnitudes reported in titles are from Rogers et al. (1991). Other
MSL Slemmons et al. (1965)
Note that dates and times given are in Pacific Standard Time to increase
local relatability and relevance; to convert to GMT add 8 hours, except
for the 1966 and 1994 events, which occurred during daylight savings time,
add 7 hours for these events.
MTO Toppozada et al. (1981)
MBM Bolt and Miller (1975)
Western Nevada Earthquake, 1852(?), M7.3
The 1852(?) western Nevada earthquake is one of the first earthquakes on
record in Nevada. Its location appears to have been in the Carson Sink
region (possibly near Stillwater). An 1869 account by a Northern Paiute,
who was a boy at the time, recalls Paiutes being knocked down by the event,
collapsed river banks in the Carson Sink area, broken ground, and the temporary
reversal of flow of the river near Stillwater Station (Gold Hill Daily
News, 12/30/1869). If the river was temporarily reversed at this location,
this is possibly a near-field, tectonic effect. Another potential effect
of this event was a large landslide that occurred at Slide Mountain in
late November or early December of 1852 (Washoe Weekly Times, 6/10/1865).
Reportedly, two men at Genoa distinctly heard and felt the shock associated
with the landslide; it is unlikely that the landslide itself caused perceptible
ground motion or noise that could be heard as far south as Genoa. It is
more likely that they heard and felt the effects of an earthquake that
caused the slide. Five people passing along the emigrant trail in the valley
below were apparently buried by this slide (Washoe Weekly Times, 6/10/1865).
Some corroboration of this account is given by a discussion of Paiute traditions,
that a great many years ago, the "whole side" of Slide Mountain came down
during an earthquake (Territorial Enterprise, 11/27/1894). The most direct
account for placing this earthquake in 1852 comes from an account in 1865
that says that the Northern Paiutes often talk about a "great" earthquake
that occurred 13 years before (Daily Reese River Reveille, 10/17/1865).
Ryall (1977) suggests this event occurred in 1845; notes by Ryall indicate
that this was based on interpreting the 1869 account strictly (the Paiute
was "a boy" at the time of the earthquake and was guessed in 1869 to be
about 30 years old) and a lack of felt reports in the Sierra Nevada in
1852. There are other accounts of earthquakes in western Nevada in the
1840s as well (e.g., Silver State News, 10/5/1915). Anderson and Hawkins
(1984) suggested that a recent break along the Pyramid Lake fault zone,
south of Pyramid Lake, may have been caused by a historical event, possibly
the 1852(?) event.
Western Nevada Earthquake, September 3, 1857, M6.2
Very little is known about this earthquake, which occurred on September
3, especially about its exact location. The first newspaper in Nevada began
in 1858. Toppozada et al. (1981) examined the intensity pattern in the
Sierra Nevada communities and concluded that the effects were similar to
the 1860, 1868, 1869, and 1887 Nevada earthquakes, and that it was likely
near the Nevada/California border. [MTO 6.0]
This earthquake caused goods to be shaken from shelves and general panic
in Carson City, although no damage was reported (Holden, 1898; Toppozada
et al., 1981). The earthquake was felt as far away as Yreka and San Francisco
in California (Toppozada et al. 1981). Toppozada et al. (1981) suggest
that the epicenter of the event was near Pyramid Lake since seven aftershocks
were reported the same day (March 15) in the Pyramid Lake area and rock
slides were reported between Pyramid Lake and Carson City. This earthquake
may have caused the young surface rupture near Derby noted by a prospector
in the 1860s; if so, the Olinghouse fault may have been the source of the
event (see discussion under 1869 Virginia Range earthquakes). Anderson
and Hawkins (1984) also mention the 1869 event as a possible cause of the
recent break along the Pyramid Lake fault zone. [MSL 7.-, MTO
This earthquake was strongly felt at Virginia City, where brick buildings
were cracked, some bricks shaken down, and plaster fell in nearly all brick
buildings (Toppozada et al. 1981). Two foreshocks were reported in Virginia
City, 14 and 5 minutes before the main event (The Daily Trespass, 5/30/1868).
Toppozada et al. (1981) comment that the intensity distribution for this
event resembles that of the 12/27/1869 earthquake. This event may have
been a foreshock to the 1869 earthquakes. [MSL 6.-, MTO
The December 26, 1869 Virginia Range earthquake strongly shook western
Nevada and eastern California. This event seriously damaged masonry walls
in Virginia City and Washoe City, and caused some damage in communities
of the Sierra Nevada foothills of California. A second large earthquake
(perhaps the largest aftershock) occurred eight hours later and strongly
shook Carson City, but reportedly did little damage. Slemmons (1969) reports
that Dr. Gianella of Mackay School of Mines interviewed a prospector from
the WadsworthOlinghouse area who reported that during the 1860s surface
faulting appeared in the Derby Dam area of the Truckee River Canyon. In
Slemmons' judgement, the largest event in the 1860s was in 1869. Thus,
Slemmons felt it was likely that this surface rupture (which he found)
was from this earthquake and that this suggests the location of the event.
This surface rupture along the Olinghouse fault was mapped by Sanders and
Slemmons (1979), who found left-lateral offsets as large as 3.7 m (12 ft).
Toppozada et al. (1981) suggest that an epicenter near Steamboat Springs
(south of the Olinghouse location) would better fit the damage distribution
and the second earthquake as an aftershock; this second event appears to
have occurred in the southern Virginia Range. It is also noted that Steamboat
Springs spouted most furiously to a height of 3 to 4.5 m (10 to 15 ft)
after the earthquake (Gold Hill Daily News, 12/27/1869). A magnitude 6.7
or larger was estimated by Sanders and Slemmons (1979) using earthquake
intensity area. [MTO 6.1 and 5.9]
This earthquake caused very strong shaking in Carson Valley. At Genoa,
houses were shifted off their foundations and bricks were thrown down (Territorial
Enterprise, 6/4/1887). At Carson City, chimneys were damaged, brick and
stone walls were damaged, and plaster fell. At the State Capitol, the west
wall was cracked and plaster fell in several rooms (Territorial Enterprise,
6/4/1887). Some people who were in the streets of Carson City that morning
(the earthquake occurred at ~2:45 a.m.) were apparently thrown to the ground
by the shock (Territorial Enterprise, 6/4/1887). At Mound House, a hotel
and wayside resort was totally destroyed by a fire on the day following
the earthquake; the earthquake had separated several joints in the stove
pipe and when the stove was lit the morning of the 4th, fire leapt out
of the break in the pipe and ignited the wood backing (Carson Daily Index,
6/5/1887). Near Cradlebaugh's Bridge, south of Carson City, a fissure 15
m (50 ft) long opened up and mud and hot water spouted for a half an hour
without abating (Reno Gazette-Journal, 10/28/1979). Springs all around
Carson City either increased in flow or went suddenly dry. General alarm
occurred in Virginia City and Reno, but there was little damage. The earthquake
appears to have occurred in Carson Valley. [MTO 6.3]
In 1914 a pair of strong earthquakes shook the Reno region; these events
occurred on February 18 and April 24 (discussed in next section). The first
event had a magnitude of about 6 (Slemmons and others, 1965). Damage in
Reno was limited to bricks falling from a chimney at the University of
Nevada, broken windows and cracked plaster (Reno Evening Gazette, 2/18/14;
A. Jones, unpublished notes). The event occurred at 10:19 a.m. (PST) and
schools and buildings were evacuated immediately. At the University of
Nevada, "the students and professors vied with one another in an attempt
to be the first outside" (Reno Evening Gazette, 2/18/14). Because the strongest
intensity of this event was to the west of Reno, it appears that this event
occurred in the Verdi area (Priestley, 1981).
The second event occurred on April 24 and had a magnitude of 6.4 (Slemmons
et al., 1965). This event brought down four chimneys at the University
of Nevada and caused considerable glass breakage in the chemistry laboratory.
Broken china and other nonstructural damage occurred in Reno. It is suggested
that at least the second event occurred to the east of Reno (Priestley,
1981), which is consistent with strong shaking at Hazen. In a 1934 correspondence
to a Californian, Gianella (a professor at the University of Nevada) judged
that the event, "was located along the Virginia Range probably near Fernley
or Wadsworth." Gianella mentions that this is only a guess, however, since
information is incomplete. Several residents said that the earthquake was
preceded by a smaller event by about five minutes (Nevada State Journal,
The Wabuska earthquake was strongly felt in western Nevada. The earthquake
was very severe in Virginia City with several chimneys knocked down and
the Catholic Church badly damaged (Reno Evening Gazette, 6/26/33). Chimneys
were thrown down in Carson City as well, and plaster fell from the assembly
chamber in the State Capitol building. Numerous rockfalls occurred around
Lake Tahoe, covering the highways. Reno was mostly spared from this event,
experiencing only Modified Mercalli Intensity V. This event was part of
a remarkably active earthquake period in western and central Nevada from
about 1932 to 1934, which includes the 1932 Cedar Mountain earthquake (M7.2)
near Gabbs. [MSL 6, MBM 6.1]
Verdi Earthquake, December 29, 1948, M6.0
On December 29, 1948, a magnitude 6.0 earthquake near Verdi caused Intensity
VII damage to that community. The main event was preceded by several foreshocks.
On December 27, notable foreshocks occurred at 5:15, 6:24, 8:21, 8:24,
9:24, and 10:04 p.m. (PST). The event at 9:24 p.m. is described as "a prolonged
jolt beneath the city [Reno] for perhaps 30 seconds." On December 28, numerous
earthquakes were felt, and at Verdi there were almost continuous vibrations.
Following a lull of nearly 36 hours, almost everyone in a radius of 80
km (50 mi) was awakened by the mainshock at 5:53 AM on December 29th. Nearly
every building in Verdi had some sort of damage. Brick parapets on the
east and west sides of the Verdi school building were sheared and thrown
off. A wall of a grocery store fell down. Several chimneys came down in
Verdi and Floriston, and bricks fell from many others. A chimney was also
broken in Dog Valley. Windows were broken as far away as Reno. A water
main between Reno and Sparks was sheared. In Verdi, stoves were knocked
out of line and in some cases went sliding into walls. Large boulders up
to 1.5 m (5 ft) came down in the Truckee River Canyon along U.S. Highway
40 south of Verdi, knocking out both power and telephone lines. Telephone
service in Reno was out for one to two days.
The earthquake is thought to have originated in Dog Valley and to have
possibly occurred along the Verdi fault (which is northerly striking as
is the orientation of the most severe damage) or the Dog Valley lineament.
In addition to foreshocks, "mysterious rumbles" or subterranean roars were
heard in the Verdi-Reno region for about a year before the Verdi earthquake
(Bell et al., 1982). [MSL 6, MBM 6.0]
Boca Valley (Truckee) Earthquake, September 12, 1966, M6.0
The 1966 Boca Valley earthquake, just northeast of Truckee, California,
caused damage to two local dams, highways, railroads and water flumes,
and some minor structural damage to buildings. Damage to highways included
cracked bridge abutments, settlement of engineered fill at abutments, slumping
and fissuring of the highway (commonly at cut and fill contacts), and slides,
slumps, and rockfalls between Boca and the Nevada/California border (Kachadoorian
et al., 1967). Rockfalls and horizontal and vertical settlement necessitated
repeated realignment and regrading of the Southern Pacific Railroad line
(Kachadoorian et al., 1967). Rockfalls from this event also punctured and
crushed the wooden flume in the Truckee Canyon, and one 20ton boulder punched
a hole in the masonry wall of the Farad powerhouse (Kachadoorian et al.,
1967). Building damage consisted mostly of toppled chimneys, but two buildings
were racked badly. In Reno and Carson City, plaster fell and loose objects
were knocked from shelves.
The 1966 earthquake appears to have been a left-lateral strike-slip
event that occurred along the northeast-trending Dog Valley lineament (Kachadoorian
et al., 1967; Greensfelder, 1968). Aftershocks extended for 10 to 16 km
(6 - 10 mi) along a northeast trend with a vertical dip (Kachadoorian et
al., 1967; Greensfelder, 1968). The location of these aftershocks was also
coincident with a zone of discontinuous, secondary or non-tectonic fracturing
(Kachadoorian et al., 1967). [MBM 6]
Double Spring Flat Earthquake, September 12, 1994, M6.0
This earthquake occurred south of Carson Valley near Double Spring Flat.
This is the mildest earthquake, in terms of its effects, in the RenoCarson
City urban corridor discussed in this paper. Due to its moderate magnitude,
the sparseness of population in the epicentral area, and the time of day,
the earthquake did only minor damage and caused no reported injuries. One
chimney was toppled and there was minor nonstructural damage in Minden,
a foundation was damaged in Double Spring Flat, and several rockfalls occurred
along roadways. Ground cracking was noted in the epicentral area, but appears
to be secondary in nature. The 1994 earthquake was a normal-left oblique-slip
event occurring along a northeast-striking fault that dips steeply to the
southeast (Ramelli, 1994; dePolo et al., 1995). Aftershocks extended over
a distance of about 12 km (7.4 mi). Several small foreshocks occurred over
a 12day period leading up to the mainshock and background seismicity notably
occurred in the area over the year or two before the event. [Mw
5.9-6.1, ML 6.0]