Abstract
We used a new data set of relocated earthquakes recorded by the Seismic Network of Northeastern Sonora, Mexico (RESNES) to characterize the attenuation of S-waves in the fault zone of the 1887 Sonora earthquake (Mw 7.5). We determined spectral attenuation functions for hypocentral distances (r) between 10 and 140 km using a nonparametric approach and found that in this fault zone the spectral amplitudes decay slower with distance at low frequencies (f < 4 Hz) compared to those reported in previous studies in the region using more distant recordings. The attenuation functions obtained for 23 frequencies (0.4 ≤ f ≤ 63.1 Hz) permit us estimating the average quality factor QS = (141 ± 1.1 )f(0.74 ± 0.04) and a geometrical spreading term G(r) = 1/r0.21. The values of Q estimated for S-wave paths traveling along the fault system that rupture during the 1887 event, in the north–south direction, are considerably lower than the average Q estimated using source-station paths from multiple stations and directions. These results indicate that near the fault zone S waves attenuate considerably more than at regional scale, particularly at low frequencies. This may be the result of strong scattering near the faults due to the fractured upper crust and higher intrinsic attenuation due to stress concentration near the faults.Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-3-747) contains supplementary material, which is available to authorized users.
Highlights
On May 3, 1887, a mayor seismic event (Mw = 7.5) took place on northeastern Sonora (Mexico), destroying the town on Bavispe and its surroundings (Aguilera, 1888)
Attenuation functions using a nonparametric method We explore the dependence of the spectral amplitudes with hypocentral distance by considering that for a fixed frequency, the spectral amplitudes can be represented by empirical determined functions obtained following a model that separates source size from attenuation effects (e.g. Castro et al, 1990; Anderson and Lei, 1994; Castro et al, 1996; Castro et al, 2008)
Attenuation functions The spectral amplitudes modeled with equation (1) describe the S-wave attenuation in northeastern Sonora, in the region close to the rupture zone of the 1887 (MW = 7.5) earthquake
Summary
On May 3, 1887, a mayor seismic event (Mw = 7.5) took place on northeastern Sonora (Mexico), destroying the town on Bavispe and its surroundings (Aguilera, 1888). This event, as well as most northern Mexico, is located south of the Basin and Range province (Suter and Contreras, 2002), and generated the longest recorded normal fault surface rupture (101.8 km) in historic time (Suter, 2006). We use in this article a new and more complete data set to study in more detail the seismic attenuation near the fault zone This new data set is composed by earthquakes relocated by Castro et al (2010) near the faults that rupture during the 1887 event. We compare results from previous studies of spectral attenuation in the Sonora region with our new results and with results from other studies within the Basin and Range province
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