Spectral inversion of Lg from earthquakes: A modified method with applications to the 1995, western Texas earthquake sequence

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Year of Publication: 
1998
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Bulletin of the Seismological Society of America
Journal Date: 
Dec
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Volume: 
88
Issue: 
6
Pages: 
1525-1537
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ISBN Number: 
0037-1106
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ISI:000077914300018
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Abstract: 

Spectral inversion of Lg from earthquake sources is subject to significant errors, due to random and systematic deviation of the Lg spectra from idealized theoretical models. I present an analysis of these errors and demonstrate that their effects tend to increase with decreasing frequency and recording distance. I propose modifications to the inverse method of Xie (1993) to reduce these errors. The modifications include a more robust Q estimator and the added capability of incorporating a priori knowledge into the inversion. The modified method is applied to Lg spectra from the 1995, western Texas earthquake (M-W = 5.7), I measured average two-station Q values for selected station pairs, as well as the source rise time of the mainshock, with an empirical Green's function approach. These served as a priori knowledge for the simultaneous inversion for Lg seismic moment (M-0), corner frequency (f(c)), and path Q. The result of the inversion indicates that Lg source radiation is nearly isotropic. The M-0 and f(c) values estimated using Lg from the mainshock and two aftershocks are typical for Lg from central and eastern North American earthquakes, with M-0 scaling with f(c)(-4), and M-0 and f(c) being 3.3 x 10(16) N-m and 0.3 Hz, respectively, for the mainshock. The 1-Hz Lg Q correlates with tectonic environments, increasing from about 200 for westerly paths to above 700 for easterly paths. Two-station Q measurements suggest that, as previously discovered for Eurasia, the frequency dependence of Lg Q may be variable with distance if the distance spans a wide range (10(3) km).

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154XATimes Cited:9Cited References Count:32

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