Shear-Wave Attenuation Study in the South Region of the Gulf of California, Mexico
Por:
Castro, Raul R., Singh, Shri K., Joshi, Anand, Singh, Sandeep
Publicada:
1 abr 2019
Resumen:
We study the variability of the quality factor Q(S) with depth (1D
model) using S-wave recordings from regional stations of the Broadband
Seismological Network of the Gulf of California (GoC) (RESBAN) operated
by Centro de Investigacion Cientifica y de Educacion Superior de
Ensenada (CICESE). We analyzed earthquakes located by Sumy et al. (2013)
in the southern gulf with hypocenters determined using ocean-bottom
seismographs of the Sea of Cortez Ocean Bottom Array (SCOOBA) experiment
and onshore stations of the Network of Autonomously Recording
Seismographs (NARS)-Baja array. We also used events relocated by Castro
et al. (2017b) in the same region. This catalog of seismicity within the
North America-Pacific plate boundary permits us to study the attenuation
characteristics of the S waves in greater detail than previous studies,
because the new data set samples more densely the gulf region. We
determined nonparametric attenuation functions in the 10-250 km distance
range to estimate Q(S) at different frequencies and depths. To estimate
Q(S), the geometrical spreading function G(r) is taken as 1/r for r <
100 km and 1/root r for r >= 100 km. We found that at 4 Hz Q(S) similar
to 770 for the first 5 km, increasing to similar to 1200 up to 10 km
depth, where Q(S) starts to gradually decrease, reaching a value of Q(S)
similar to 970 between 25 and 40 km depth. This increase in attenuation
at 10-40 km depth is consistent with estimates of Q(S) near the East
Pacific Rise (Yang et al., 2007). In general, our average estimates of
Q(S), which include spreading centers and basins, are higher than those
reported in other ridge zones. This indicates that zones of high
attenuation in the GoC may be restricted to regions near the spreading
centers. We also used the function G(r) = 1/r, which corresponds to the
dominance of body waves at all distances, and we found that at low
frequencies (f < 4 Hz) this function gives similar values of Q(S) as
those estimated with the spreading function that introduces a weaker
decay with distance at r > 100 km.
Filiaciones:
Castro, Raul R.:
CICESE, Div Ciencias Tierra, Dept Sismol, Carretera Tijuana Ensenada 3918, Ensenada 22860, Baja California, Mexico
División Ciencias de la Tierra, Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Carretera Tijuana-Ensenada No. 3918, Ensenada, Baja California 22860, Mexico
Singh, Shri K.:
Univ Nacl Autonoma Mexico, Inst Geofis, Ciudad Univ, Mexico City 04510, DF, Mexico
Instituto de Geofísica, UNAM, Ciudad Universitaria, México, 04510, Mexico
Joshi, Anand:
Indian Inst Technol, Dept Earth Sci, Roorkee 247667, Uttar Pradesh, India
Department of Earth Sciences, Indian Institute of Technology, Roorkee, Roorkee, Uttarakhand 247667, India
Singh, Sandeep:
Indian Inst Technol, Dept Earth Sci, Roorkee 247667, Uttar Pradesh, India
Instituto de Geofísica, UNAM, Ciudad Universitaria, México, 04510, Mexico
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