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Bulletin of the Seismological Society of America, Vol. 95, No. 6, pp. 22592271, December 2005, doi: 10.1785/0120040145
Stochastic Modeling of the 30 September 1999 Mw7.5 Earthquake,
Oaxaca, Mexico
by Raul R. Castro and Euclides Ruz-Cruz
Abstract We used the stochastic method proposed by Beresnev and Atkinson(1997, 1998a) for finite faults to model the 30 September 1999 Mw 7.5 Oaxaca,
Mexico earthquake. This large intraplate event was located close to the coast and
caused important damage in the state of Oaxaca. We modeled acceleration records
from 10 strong-motion stations located near the rupture and at regional distances.
The site response of the stations used was determined using more than 100 additional
records from other events recorded at the sites of interest. We estimated average
spectral ratios between horizontal and vertical components of ground motion ( HVSR
method), and we incorporated the site response estimates in the stochastic simula-
tions. We also analyzed the decay of the observed spectral amplitudes with hypo-
central distance and estimated the attenuation relation to be Qs 416.5 f0.7. The
main event had a normal-faulting mechanism with a fault plane 90 km long and 45km wide. We divided the fault plane into 9 5 subfaults to apply the point-source
formalism. Specific slip weights were prescribed on the individual subfaults using
the slip distribution obtained by Hernandez et al.(2001). Then, we looked for values
of the radiation-strength factor (sfact) and the stress parameter (r) that gave the
minimum model bias of the acceleration response spectra. We found that sfact 1
and r 90 bars provided the best fit to the observed response spectra and peak
ground acceleration (PGA). These results will be useful to estimate the regional PGA
generated by earthquakes with similar source characteristics as the 30 September
1999 event.
Introduction
The Oaxaca, Mexico, earthquake of 30 September 1999
(Mw 7.5) was located below the coast at a depth of 40 km
(16.00N, 97.02E), near the aftershock area of the 29
November 1978 (Mw7.7) thrust event (Singh et al., 2000).
The Oaxaca 1999 event was a normal-faulting intraplate
earthquake. The Harvard centroid moment tensor (CMT) fo-
cal mechanism solution gives a nodal plane dipping north-
east that can be considered as the fault plane (dip, 50; strike,
295; rake, 82). Based on local and regional data, Singh
et al. (2000) suggested that the rupture propagated toward
the northwest. They estimated a total rupture duration of
14.5 sec and a seismic moment M0of 2.0 1027 dyne cm.
Hernandezet al. (2001) also studied this earthquake using
near-source strong-motion records. They determined the slip
distribution on the fault and found that the rupture propa-
gated from east-southeast to west-northwest with an average
rupture velocity of 3 km/sec.
In the epicentral area, near the coast, intensities accord-
ing to the Mercalli Modified scale (MM) of VIIVIII were
reported in San Pedro Mixtepec and Puerto Escondido. In
the city of Oaxaca, intensities of VIVII were reported.
Models to simulate the ground motion generated by intra-
plate events in the subducted slab are important because
these earthquakes tend to cause more damage than other
events with comparable magnitude. For instance, Singh et
al.(1980) found that for earthquakes of the same magnitude,
the area experiencing MM intensity VI is about four times
greater for intraslab events than for interplate earthquakes.
They observed that in Mexico, interplate events show larger
attenuation than intraplate events. They suggested, as a pos-
sible explanation, the higher scattering and viscous losses
from interplate earthquakes, which occur near the trench of
the subduction zone.
In this article, we use strong-motion records from 10
stations azimuthally well distributed to find the necessary
source and propagation parameters for the stochastic model
proposed by Beresnev and Atkinson (1997, 1998a, 1998b).
Data
Figure 1 shows the distribution of the 10 stations se-
lected for the analyses and the location of the earthquake
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Figure1. Epicentral location of the 30 September, 1999 (Mw 7.5) earthquake anddistribution of stations used. The focal mechanism and the rupture area are also shown.At the bottom of the figure a section along AA (modified from Sing et al. 2000) isshown.
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Stochastic Modeling of the 30 September 1999 Mw 7.5 Earthquake, Oaxaca, Mexico 2261
Table 1Station Coordinates (from the Mexican Strong Motion Database, 2000)
Stat. Code Name
Lat N
(Deg)
Long W
(Deg)
r
(km)
PGA
(cm/sec2)
Mean PGA
(cm/sec2)
fmax
(Hz)
Instrument
Type
LANE Las Negras 15.948 97.187 43.1 251.8 245.4 7.94 Altus-Etna
RIOG Ro Grande 16.014 97.439 59.5 307.5 299.0 10.0 Altus-Etna
HUIG Huatulco 15.768 96.108 108.3 146.6 124.9 20.0 Q880; FBA-23
PNIG Pinotepa 16.392 98.127 133.1 40.44 38.0 25.0 Q680; FBA-23
OXIG Oaxaca 17.072 96.733 134.2 196.5 154.1 10.0 Q680; FBA-23
VIGA Las Vigas 16.757 99.236 255.1 68.3 60.1 10.0 Altus-Etna
TEMC Temascal 18.228 96.415 263.5 96.6 73.5 10.0 DCA-333
MEZC Mezcala 17.930 99.591 352.2 12.3 11.1 5.0 Altus-Etna
YAIG Yautepec 18.862 99.067 390.2 17.5 15.7 10.0 Q680; FBA-23
PENB Penitas 17.433 93.450 417.5 9.4 8.5 6.5 DCA-333
epicenter. All of the available records were taken from the
Mexican Strong Motion Database (2000) (MSMD), except
those from LANE and RIOG, which were provided by the
Instituto de Ingenieria, Universidad Nacional Autonoma de
Mexico (UNAM). We selected records from stations located
on free-field sites with clear P- and S-wave arrivals and a
signal-to-noise ratio greater than 1.64 dB. Table 1 lists the
coordinates and site characteristics of these stations. Figure1 also shows the rupture area (gridded rectangle), the focal
mechanism, and a cross section showing the location of the
hypocenter with respect to the trench, the coast, and the city
of Oaxaca. This normal fault event was located at about
40 km depth (Hernandezet al., 2001) inside the Cocos plate.
The acceleration records were baseline corrected, and
then we selected time windows starting a few seconds before
theS-wave arrivals and extending until the window reaches
90% of the energy of the record. We calculated the 5%
damping response acceleration spectra for the selected win-
dows, and we use these as the observation input to model
the 30 September 1999 earthquake.
The hypocentral distances of the records range from43.1 to 417.5 km, and the average horizontal peak ground
acceleration (PGA) ranges from 8.5 to 299.0 Gal. All the
stations used are free-field sites, and most are located on hard
rock. For this reason, previous studies (Singh et al., 2000;
Hernandez et al., 2001) neglected the near-site amplification.
Nevertheless, we estimated the seismic site response of the
10 stations using horizontal-to-vertical spectral ratios
(HVSR).
Site Response Estimates
In general, site amplification is expected to occur at sta-
tions located on soft soils or sediments; however, importantamplifications have also been observed at rock sites (e.g.,
Tuckeret al., 1984; Castro et al., 1990; Humphrey and An-
derson, 1992). Although the stations selected for this study
are located on rock (see Table 1), we estimated the site re-
sponse of the 10 stations selected for the modeling using the
HVSRtechnique.
Site amplification has been estimated using HVSR of
earthquake records in the past (Lermo and Chavez-Garca,
1993; Field and Jacob, 1995; Castro et al., 1996, among
others), and the technique continues to be useful for analyz-
ing the seismic response of recording sites to S-wave inci-
dence. The fundamental assumption of the HVSRmethod is
that site amplification on the vertical component of motion
can be neglected. This assumption has recently become con-troversial because the presence of surface waves may induce
vertical amplification (Castroet al., 1997, 2004; Bindiet al.,
2004) and because S-to-P conversions can invalidate that
assumption (e.g., Bonillaet al., 2002). However, these prob-
lems can be overcome if the time window used to calculate
the spectral amplitudes contains mainly Swaves, since the
vertical amplification is minimized.
We selected all of the available records reported by the
MSMD. Most of the events used have hypocentral distances
equal or less than that from the 30 September event at the
corresponding site. For stations LANE, RIOG, HUIG, and
OXIG, we also included events with greater hypocentral dis-
tances to increase the number of spectral records and to makethe average HVSR meaningful. Table 2 lists the number of
earthquakes used for each station and the range of magnitude
and hypocentral distance of the events.
We calculated the acceleration spectra of the three com-
ponents of motion using the same windows as for the re-
sponse spectra. The spectra were smoothed using a variable
frequency band of25% of 20 predefined frequencies from
0.25 to 20.0 Hz. The length of the time window used to
calculate the spectra defines the lower limit of the frequency
band useful for further analysis, and the noise level defines
the upper limit. For all records the lower and upper limits
are before 0.25 and after 20 Hz, respectively. The time win-
dows used to calculate the spectra contain 90% of the energyof the records, starting with the first S-wave arrival. A 5%
cosine taper was applied to the beginning and end of the
record section. The length of the windows used varied be-
tween 10 and 32 sec.
To estimate the site amplification Z(f) at each station,
we calculated the arithmetic average of all events:
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M1 N(f) E(f)
Z(f) , (1) M 2V(f)i1 iwhere Mis the number of earthquakes and N(f), E(f), and
V(f) are the spectral amplitudes of the northsouth, east
west, and vertical components, respectively.
Figure 2 shows the amplification functions obtained
(solid lines) and the standard deviation of the average (dotted
lines). Most of the stations show peak amplification of less
than a factor of 3.0. Two sites have significant amplifica-
tions, but in a narrow frequency band: LANE, with a peak
amplification of 8.8 at 0.5 Hz, and TEMC, with amplification
of 8.4 at 3.0 Hz. The frequencies at which the peak ampli-
fication occurs are likely related to the natural frequency of
vibration of the sites.
Simulation Method
Stochastic Model
We used a finite-fault model and the stochastic method
proposed by Beresnev and Atkinson (1997, 1998b) to sim-
ulate the observed records of the 30 September 1999, (Mw7.5) Oaxaca, Mexico, earthquake. In this model the fault
plane is divided into equal rectangular subfaults. Then, the
subfaults are treated as point sources with x2 spectra, and
the contribution of each subfault is summed, assuming that
the rupture propagates radially from the hypocenter. To cal-
ibrate the input parameters of the model, we defined the
bias as
n1 PSA(f)obs
E(f) log , (2) n PSA(f)i1 isimwhere nis the number of stations and PSA(f) are the response
acceleration spectra. The simulated PSA(f)sim was obtained
using the code FINSIM (Beresnev and Atkinson. 1998a).
This code has been validated in diverse tectonic environ-
ments for ground-motion prediction (Hartzell et al., 1999;
Berardiet al., 2000; Castro et al., 2001; Beresnev and At-
kinson. 2002; Hough et al., 2002, among others). We also
defined an average error (e) for the frequency band used as
m1
e |E(f)| , (3) jm j1
wherem is the number of frequencies used to calculate the
average.
Fault Discretization
Singh et al. (2000) estimated the rupture area of the
main event from the aftershock distribution and found a fault
length of 90 km and a width of 45 km. In order to apply the
point source approximation used by the code, we divided the
fault plane into subfaults. We calculated the size of the sub-
faults using the magnitudelength relation obtained by Be-
resnev and Atkinson (1999):
logDl 2 0.4M , (4)
where Dlis the subfault length and M(7.5) is the magnitude.
Assuming that Dl Dw, where Dw is the subfault width,
we divided the rupture area into 9 5 subfaults. Note that
this assumption makes the simulated fault width 5 km
greater than that reported by Singh et al. (2000). However,
this amount is within the expected error of the aftershock
area estimation.
We weighted the contribution of the individual subfaults
to the total seismic moment (M02.0 1027 dyne cm) using
the slip distribution obtained by Hernandez et al. (2001)(Fig. 3). We also used the fault geometry corresponding to
the Harvard CMT solution (dip, 50; strike, 295; rake,
82).
Duration of Time Window
In the FINSIM code, the duration of the subfault time
window (Tw) is represented as the sum of its source duration
(T) and a distance-dependent term (Td)
T T T (r) (5)w d
Ruz-Cruz (2004) analyzed different functions of Td andfound that the relation determined by Atkinson (1995) from
subduction zone earthquakes provides the best approxima-
tion to the durations observed for the 30 September event.
The Radiation-Strength Factors
In the stochastic model, the level of high-frequency ra-
diation is controlled by the radiation-strength factor s, and
this parameter is related to the maximum slip velocity on the
Table 2Ranges of Magnitudes and Hypocentral Distances of Additional
Evens Used to Estimate the Site Response
Station Site Geology
Number of
Ev ents M agn itud es
Hypocentral
Distance (km)
LANE Rock 6 4.45.2 488
RIOG Rock 4 4.55.2 30170
HUIG Rock 11 4.45.2 30142OXIG Diorite 10 3.95.2 100179
PNIG Rock 8 4.15.6 17128
VIGA Rock 52 3.55.0 18255
MEZC Rock 7 4.65.9 124286
YAIG Rock 6 4.65.6 241390
TEMC Shale 7 4.24.9 82263
PENB Rock 4 5.06.5 143417
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Stochastic Modeling of the 30 September 1999 Mw 7.5 Earthquake, Oaxaca, Mexico 2263
Figure2. Site response estimated using horizontal-to-vertical spectral ratios. Thesolid line is the average value, and the dashed line the mean 1 standard deviation.
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Figure3. Slip distribution reported by Hernandezet al. (2001).
fault (Beresnev and Atkinson, 2002). We tested values ofsbetween 0.5 and 2.0.
The Stress Parameter r
The seismic moment of the subfault (m0) is related to
its length Dl (Beresnev and Atkinson, 1997) by
rm . (6)0 3
Dl
Since m0 has major influence on the low-frequency ampli-
tudes, variations in r tend to have a greater effect on the
spectral amplitudes at lower frequencies than factor s. Weperformed simulations varying the stress parameter between
30 and 200 bars.
Cutoff Frequency fmax
The value of fmax for the high-frequency filter (Boore,
1983) used by the simulation code was selected visually
from the observed acceleration spectra. Table 1 lists the val-
ues picked for each station. fmax is the frequency at which
the spectral amplitudes start to abruptly decay.
Attenuation Model
As mentioned before, the strong-motion records of the
30 September 1999 earthquake were recorded at a distance
range of 43418 km. At local distances (r 110 km) only
3 of the 10 stations analyzed recorded the main event
(LANE, RIOG, and HUIG). In this distance range, Castro
and Mungua (1993) found a Qfrequency relation (Q
56f) by using S waves from local earthquakes recorded in
the region of Oaxaca. Similar relations based on coda waves
have been reported for Oaxaca (Acosta-Chang, 1980; Rod-
riguez, 1985), but they are also valid for local distances
(r 100 km). Other studies such as that by Canas et al.
(1988) estimated the attenuation ofLgwaves in the OaxacaChiapas region in the frequency band 0.71.7 Hz. Most re-
cently, Ottemoller et al.(2002) found an average Lgquality
factor for southern Mexico, QLg(f) 204f0.85 in the fre-
quency range 1.68 Hz, using crustal earthquakes recorded
at distances greater than 200 km. This relation is similar to
the S-wave Q-frequency relation obtained by Ordaz and
Singh (1992) from a spectral attenuation study of subduction
zone earthquakes recorded in Guerrero and the Valley of
Mexico, namely Q 273f0.66.
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Stochastic Modeling of the 30 September 1999 Mw 7.5 Earthquake, Oaxaca, Mexico 2265
Figure 4. Vertical component S-wave accelerationspectra of the 30 September, 1999 earthquake. Thesolid line corresponds to station Pinotepa (PNIG), lo-cated at 133.1 km.
In order to find an attenuation relation useful for the
whole distance range and frequency band of the 30 Septem-
ber 1999 data, we used the acceleration spectra to determine
the spectral amplitude decay with hypocentral distance at
each frequency analyzed. To minimize the amplification due
to site effects, we considered only the vertical components
for these estimates. Figure 4 shows the S-wave acceleration
spectra calculated using the vertical components and thesame procedure mentioned before. The spectrum of station
PNIG (r 133.1 km), plotted as a solid line, shows signifi-
cantly low amplitudes at frequencies f 5 Hz. compared
with stations located at even greater hypocentral distance.
We believe this deamplification may be due to either strong
near-site attenuation or a radiation pattern effect.
The observed spectral amplitude U(r, f) at frequency f
and hypocentral distanceris modeled as
pfr/QbU(r, f) S G(r) e , (7)
whereSis a scalar that depends on the source effects, G(r)
is the geometrical spreading, bis the S-wave velocity, andQaccounts for anelasticity effects.
The site effects are neglected in equation (7) because
we use the vertical component of motion. The geometrical
spreading functionG(r) was assumed to have the following
form:
1/r, r 100 kmG(r) . (8)1/2(100 r) , r 100 km
Equation (8) accounts for the expected amplitude decrease
of body waves atr 100 km and for the presence of surface
waves at longer hypocentral distances (Aki and Richards,
1980). Note also that atr 100 km, equation (8) preservescontinuity. This simple functional form of the geometrical
spreading has been useful for estimating Q in other regions
of Mexico (see for instance, Castro et al., 1990; Ordaz and
Singh, 1992).
For a given frequency f, the spectral amplitudes can be
modeled as a function of distance ras follows:
u(r) b m r, (9)
whereu(r) log [U(r,f)/G(r)],b logS, andm pf/bQ
log (e). We used an average shear-wave velocity bof 3.66
km/sec, calculated from the crustal model determined by
Valdes et al. (1986) for Oaxaca, which is similar to the
model by Nava et al. (1988) for the same area. Figure 5
shows the linear fit obtained for a sample of six frequencies.
We measured the slope of the fit (m) to estimate the quality
factorQ. For these estimates, we did not use station PNIG
because of the anomalously low spectral amplitudes ob-
served, particularly at f 5 Hz. However, station OXIG is
at about the same distance and permits a good definition of
the amplitude decay. Figure 6 shows the values estimated
for all frequencies analyzed and the Q-frequency relation
found (Q 416.5 1.1f0.70.1). It is interesting to note
that thisQrelation predicts lower attenuation compared with
Q 56f, obtained by Castro and Munguia (1993) using
interplate earthquakes, consistent with the contrasting atten-
uation of intensity observed by Singh et al.(1980) between
interplate and intraplate earthquakes.
Results
To analyze the effect of different combinations of the
parameterss and r on the fitting error, we constructed the
solution space shown in Figure 7, modeling the 10 stations
in the entire frequency band (0.25 f 20 Hz). First, we
calculated the model bias with equation (2), using the am-
plitude response of all stations, and then we calculated the
average error with equation (3) for all frequencies analyzed
(30 frequencies). It can be seen in Figure 7 that the best
combination corresponds to r 90 bars and s 1.0.
Figure 8 shows the model bias calculated with the pa-
rameters of the final model. Note that the average ratio be-
tween the observed and simulatedPSAis less than 1.3 within
the frequency range 210 Hz, indicating a good agreement
in that frequency band.
The model parameters that provide the best fit between
observed and simulated acceleration response spectra (PSA)
are listed in Table 3. Figure 9 compares the observed (solid
line) and simulated (dashed line) PSA. Stations PNIG and
VIGA, located at about the same backazimuth, seem to be
overestimated, especially at lower frequencies. This may be
a radiation pattern effect not accounted for in the simulation,
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Figure5. Observed spectral amplitudes versus hypocentral distance for six differentfrequencies (0.520 Hz). The amplitudes were corrected for geometrical spreading (seeequation 8 in text). The solid line is the least-squares fit of the data, shown withtriangles.
Figure6. S-wave Q estimates. The left frame shows 1/Q 1 standard deviationand the right frame the Qfrequency relation obtained (solid line). The triangles showthe individual estimates ofQ obtained from functions shown in Figure 5.
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Stochastic Modeling of the 30 September 1999 Mw 7.5 Earthquake, Oaxaca, Mexico 2267
Figure7. Average error calculated for different combinations ofrand radiation strengthfactor (sfact). We used all stations and the entire frequency band (0.2520.0 Hz).
since this correction is assumed to be a constant average
value of 0.55 in the FINSIM code (Beresnev and Atkinson,
1998a). For the other stations, the simulated PSA follows
closely the observed values. Figure 10 shows a sample of
three acceleration time series simulated using the final
model. For comparison, we also plotted the observed north
component accelerogram. The observed records start with
the P arrival and reach the peak acceleration when the S
waves arrive. The simulated acceleration time series shown
in Figure 10 contain only the S-wave arrivals.
The observed average peak acceleration (PGA) and that
resulting from the simulation of all stations are displayed in
Figure 11 as a function of hypocentral distance. The circles
are the arithmetic average of the observed horizontal com-
ponents, and the crosses show the simulated peak accelera-
tion. We also plotted in Figure 11 the regression line ob-
tained by Singh et al. (2000) using data from rock sites that
recorded the 30 September 1999 earthquake, including the
10 stations used in this study. The local stations LANE (at
43.1 km) and RIOG (at 59.5 km) show a discrepancy be-
tween simulated and observed PGA. However, at longer hy-
pocentral distances, the simulated PGA values are close to
either the observed values or the regression function of
Singh et al. (2000). Overall the agreement is satisfactory
given the significant scatter.
Conclusions
We determined the site response of 10 stations to find
a stochastic model to estimate the ground motion generated
by the 30 September 1999 (Mw 7.5) earthquake. Although
most of the stations showed small site amplification, below
a factor of 3.0, two sites had significant amplifications, but
in a narrow frequency band. LANE had a peak amplification
of 8.8 at 0.5 Hz, and TEMC an amplification of 8.4 at 3.0 Hz.
We found an attenuation relation valid for the entire
distance range and frequency band of the data set analyzed,
namely Q 416.5f0.7, with an associated geometrical
spreading model of r1 at r 100 km and r0.5 at
r 100 km. With this relation and dividing the fault rupture
into 9 5 subfaults of 10 km size (Dw Dl), we find a
radiation-strength factor s 1.0 and a stress parameter
r 90 bars. These parameters, obtained from the stochastic
modeling, reproduce reasonably well the observed PSA, par-
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Figure 8. Model bias calculated using equation(2) and the final model parameters listed in Table 3.The solid line is the average, and the dotted lines theaverage 1 standard deviation.
Table 3Final Model Parameters
Parameter Value Reference
Fault orientation Strike, 295;dip, 50
Singh et al.(2000)
Fault dime nsions Length, 90 km,
Width, 50 km
Singh et al.(2000)
This study
Location of rupture
initiation point
16.00 N,
97.02 E
Singh et al.(2000)
Focal depth 40 km Hernandez et al. (2001)
Magnitude MW7.5 Singh et al.(2000)
Seismic moment Mo2.0 1027
dyne cm
Harvard CMT
catalog
Shear-wave velocity
and density
b 3.66 km/sec
q 2.8 g/cm3Valdeset al. (1986)
Q(f) 416.5 f0.7 This study
Geometrical spreading 1/R, R 100 km
1/(100R)1/2,
R 100 km
Number of subfaults 9 5 This study
Subfault corner frequency 0.16 Hz This study
Stress parameter 90 bars This study
Radiation-strength factor 1.0 This study
ticularly at intermediate (100 km) and longer (200
400 km) distances.
Acknowledgments
We thank Leonardo Alcantara from the Institutode Ingeniera, UNAM,
for providing the records from stations LANE and RIOG. One of the au-
thors (E.R.C.) was supported by a scholarship from the National Council
of Science and Technology of Mexico (CONACYT). Luis Inzunza helpedus prepare some figures. The comments and suggestions of the two anon-
ymous referees helped us improve the manuscript. We are grateful for their
careful revision.
References
Acosta-Chang, J. G. (1980). Estudio de atenuacion de ondas ssmicas en el
area del terremoto de Oaxaca del 30 de Noviembre de 1978.Masters
Thesis, Centro de Investigacion Cientfica y de Educacion Superior
de Ensenada, 71 p.
Aki, K., and P. G. Richards (1980). Quantitative Seismology: Theory and
Methods, W. H. Freeman, San Francisco.
Atkinson, G. M. (1995). Attenuation and source parameters of earthquakes
in the Cascadia region,Bull. Seism. Soc. Am. 85, 13271342.
Berardi, R., M. J. Jimenez, G. Zonno, and M. Garca-Fernandez (2000).Calibration of stochastic finite-fault ground motion simulations for
the 1997 Umbria-Marche, central Italy, earthquake sequence, Soil
Dyn. Earthquake Eng.20, 315324.
Beresnev, I. A., and G. M. Atkinson (1997). Modeling finite-fault radiation
fromxn spectrum,Bull. Seism. Soc. Am. 87, 6784.
Beresnev, I. A., and G. M. Atkinson (1998a). FINSIMa FORTRAN pro-
gram for simulating stochastic acceleration time histories from finite
faults,Seism. Res. Lett. 69, 2732.
Beresnev, I. A., and G. M. Atkinson (1998b). Stochastic finite-fault mod-
eling of ground motions from the 1994 Northridge, California, earth-
quake. I. Validation on rock sites, Bull. Seism. Soc. Am. 88, 1392
1401.
Beresnev, I. A., and G. M. Atkinson (1999). Generic finite-fault model for
ground-motion prediction in eastern North America,Bull. Seism. Soc.
Am. 89, 608625.
Beresnev, I. A., and G. M. Atkinson (2002). Source parameters of earth-
quakes in eastern and western North America based on finite-fault
modeling,Bull. Seism. Soc. Am. 92, 695710.
Bindi, D., R. R. Castro, G. Franceschina, L. Luzi, and F. Pacor (2004). The
19971998 UmbriaMarche sequence (central Italy): source, path,
and site effects estimated from strong motion data recorded in the
epicentral area, J. Geophys. Res. 109, B04312, doi 10.1029/
2003JB002857.
Bonilla, L. F., J. H. Steidl, J. C. Gariel, and R. J. Archuleta (2002). Borehole
response studies at Garner Valley downhole array, southern Califor-
nia,Bull. Seism. Soc. Am. 92, 31653179.
Boore, D. M. (1983). Stochastic simulation of high-frequency ground mo-
tions based on seismological models of the radiated spectra, Bull.
Seism. Soc. Am. 73, 18651894.
Canas, J. A., L. L. L. Pujades, and J. J. Egozcue (1988). Anelastic attenu-
ation Q and attenuation ofLg waves in the region OaxacaChiapasof southern Mexico,Rev. Geofis. 44, 129134.
Castro, R. R., and L. Mungua (1993). Attenuation ofP- and S-waves in
the Oaxaca. Mexico subduction zone, Phys. Earth Planet. Interiors
76, 179187.
Castro, R. R., J. G. Anderson, and S. K. Singh (1990). Site response, at-
tenuation and source spectra ofSwaves along the Guerrero, Mexico,
subduction zone,Bull. Seism. Soc. Am. 80, 14811503.
Castro, R. R., M. Mucciarelli, F. Pacor, and C. Petrungaro (1997). S-wave
site response estimates using horizontal to vertical spectral ratios,
Bull. Seism. Soc. Am. 87, 256260.
8/11/2019 Articulo R Castro - E Ruiz - 2259
11/13
Stochastic Modeling of the 30 September 1999 Mw 7.5 Earthquake, Oaxaca, Mexico 2269
Figure9. Acceleration response spectra (PSA). Solid and dashed lines are observedand simulated PSA, respectively.
8/11/2019 Articulo R Castro - E Ruiz - 2259
12/13
2270 R. R. Castro and E. Ruz-Cruz
Figure10. Acceleration time series: observed northsouth component on the leftand simulated on the right.
Castro, R. R., F. Pacor, D. Bindi, G. Franceschina, and L. Luzi (2004). Site
response of strong motion stations in the Umbria, central Italy, region,
Bull. Seism. Soc. Am. 94, 576590.
Castro, R. R., F. Pacor, A. Sala, and C. Petrungaro (1996). Swave atten-
uation and site effects in the region of Friuli, Italy, J. Geophys. Res.
101, 22,35522,369.
Castro, R. R., A. Rovelli, M. Cocco, M. Di Bona, and F. Pacor (2001).
Stochastic simulation of strong-motions records from the 26 Septem-
ber 1997 (Mw 6). UmbriaMarche (central Italy) earthquake, Bull.
Seism. Soc. Am. 91, 2739.
Centroid Moment Tensor (CMT) Catalog, www.seismology.harvard.edu/
CMTsearch.html (last accessed July 2004).
Field, E. H., and K. H. Jacob (1995). A comparison and test of various site-
response estimation techniques, including three that are not reference-site dependent.Bull. Seism. Soc. Am. 85, 11271143.
Hartzell, S., S. Harmsen, A. Frankel, and S. Larsen (1999). Calculation of
broadband time histories of ground motion: comparison of methods
and validation using strong ground motion from the Northridge earth-
quake,Bull. Seism. Soc. Am. 89, 14841504.
Hernandez, B., N. M. Shapiro, S. K. Singh, J. F. Pacheco, F Cotton, M.
Campillo, A. Iglesias, V. Cruz, J. M. Gomez, and L. Alcantara (2001).
Rupture history of the September 30, 1999 intraplate earthquake of
Oaxaca, Mexico (Mw 7.5) from inversion of strong-motion data,
Geophys. Res. Lett. 28, 363366.
Hough, S. E., S. Martin, R. Bilham, and G. M. Atkinson (2002). The 26
January 2001 M7.6 Bhuj. India earthquake: observed and predicted
ground motions,Bull. Seism. Soc. Am. 92, 20612079.
Humphrey, J. R., and J. G. Anderson (1992). Shear-wave attenuation and
site response in Guerrero, Mexico, Bull. Seism. Soc. Am. 81, 1622
1645.
Lermo, J., and F. J. Chavez-Garca (1993). Site effect evaluation using
spectral ratios with only one station, Bull. Seism. Soc. Am. 83, 1574
1594.
Mexican Strong Motion Database (2000). Sociedad Mexicana de Ingeniera
Ssmica. CD-ROM, Vol. 2, December 2000.
Nava, F., F. Nunez-Cornu, D. Cordoba, M. Mena, J. Ansorge, J. Gonzalez,
M. Rodrguez, E. Banda, S. Mueller, A. Udas, M. Garca-Garca, and
G. Calderon (1988). Structure of the Middle America trench in Oa-xaca, Mexico, Tectonophysics154,241251.
Ordaz, M., and S. K. Singh (1992). Source spectra and spectral attenuation
of seismic waves from Mexican earthquakes, and evidence of ampli-
fication in the hill zone of Mexico City, Bull. Seism. Soc. Am. 82,
2443.
Ottemoller, L., N. M. Shapiro, S. K. Singh, and J. F. Pacheco (2002). Lat-
eral variation ofLgwave propagation in southern Mexico,J. Geophys.
Res. 107,B1, doi 10.1029/2001JB000206.
Rodriguez, M. (1985). Efectos de atenuacion, fuente y sitio de las replicas
del temblor de Oaxaca (Ms 7.8), ocurrido el 29 de noviembre de
8/11/2019 Articulo R Castro - E Ruiz - 2259
13/13
Stochastic Modeling of the 30 September 1999 Mw 7.5 Earthquake, Oaxaca, Mexico 2271
Figure11. Peak ground acceleration versus hypo-central distance. Circles are observations, crossessimulations, and the line is the regression curve ob-tained by Singh et al. (2000).
1978,Masters Thesis, Centro de Investigacion Cient fica y de Edu-
cacion Superior de Ensenada, 55 p.
Ruz-Cruz, E. (2004). Modelo estocastico para simular la aceleracion del
terreno generada por el temblor de Oaxaca (Mw 7.5) del 30 de
septiembre de 1999, Masters Thesis, Centro de Investigacion Cien-
tfica y de Educacion Superior de Ensenada, 122 p.
Singh, S. K., M. Reichle, and J. Havskov (1980). Magnitude and epicenter
estimations of Mexican earthquakes from isoseismic maps, Geofis.
Int. (Mexico) 19, 269284.
Singh, S. K., M. Ordaz, L. Alcantara, N. Shapiro, V. Kostoglodov, J. F.Pacheco, S. Alcocer, C. Gutierrez, R. Quaas, T. Mikumo, and E.
Ovando (2000). The Oaxaca earthquake of 30 September 1999
(Mw 7.5): a normal-faulting event in the subducted Cocos plate,
Seism. Res. Lett. 71, 6778.
Tucker, B. E., J. L. King, D. Hatzfeld, and I. L. Nersesov (1984). Obser-
vations of hard-rock sites, Bull. Seism. Soc. Am. 74, 121136.
Valdes, C. M., W. D. Mooney, S. K. Singh, R. P. Meyer, C. Lomnitz, J. H.
Luetgert, C. E. Helsley, B. T. R. Lewis, and M. Mena (1986). Crustal
structure of Oaxaca, Mexico, from seismic refraction measurements.
Bull. Seism. Soc. Am. 76, 547563.
Centro de Investigacion Cientfica y deEducacion Superior de Ensenada (CICESE)Division Ciencias de la Tierra
Departamento de SismologaKm 107 carretera Tijuana-Ensenada, EnsenadaBaja California 22860, [email protected]
Manuscript received 6 August 2004.
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