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Broad-Band Modelling of Regional Seismograms: the Basin and Range Crustal Structure

Song, Xi J. and Helmberger, Donald V. and Zhao, L. (1996) Broad-Band Modelling of Regional Seismograms: the Basin and Range Crustal Structure. Geophysical Journal International, 125 (1). pp. 15-29. ISSN 0956-540X. doi:10.1111/j.1365-246X.1996.tb06531.x.

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Three-component broad-band displacement seismograms with paths sampling the Basin and Range province are studied to constrain the crustal structure. To find an average model that fits the data in both absolute time and waveform, we generate broad-band reflectivity synthetics and conduct sensitivity tests on different parts of a layered crustal model, where only a few layers are involved. Generalized rays are used to help identify the various phases. It proves useful to decompose a regional seismogram into segments so that the impact of model parameters on each segment can be clearly identified. Thus, for mid-crustal earthquakes, it is established that the top crustal layer controls the Rayleigh wave, the Airy phase, in shape over the range from 300 to 600 km, and the crustal layer just above the source depth controls its timing. The P_nl waves, the P_n and P_L portion, are controlled in broad-band character by the mid-crust while the top layer contributes to their long-period motion. These crustal parameters control the tangential motion similarly. The SV wave, the segment between the P_nl wave and the Rayleigh wave, is mostly controlled by the shear velocity of the lower crust. In judging the goodness of fit between the array observations and synthetic waveforms, we allow individual data segments to shift relative to the 1-D synthetics by a few seconds to account for some lateral variation. The amount of time shift is found by the cross-correlation in displacement between the data segment and the synthetics. Applying these tests in a forward modelling approach, we find that a simple two-layer crustal model is effective in explaining this data set. In this model, the main crustal layer has P and S velocities of 6.1 km s^(-1) and 3.6 km s^(-1), similar to those found by Langston & Helmberger (1974). A surface layer of thickness 2.5 to 3.5 km is required to fit the Rayleigh waves. The refined model can be used as a reference model for further studies in this region.

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Additional Information:© 1996 RAS. Accepted 1995 October 3. Received 1995 October 2: in original form 1995 May 19. We thank Lianshe Zhao for his help throughout this study. Chandan Saikia wrote the modified frequency-wavenumber algorithm. Craig Scrivner, Bradley Woods, Lupei Zhu, David Harkrider, Chandan Saikia, John Cassidy and one anonymous reviewer reviewed the manuscript. This research was supported by the Air Force through grant number F49620-93-1-0221. Contribution No. 5548, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California.
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Air Force Office of Scientific Research (AFOSR)F49620-93-1-0221
Subject Keywords:Basin and Range; broad band; crustal structure; seismograms
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Caltech Division of Geological and Planetary Sciences 5548
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:39051
Deposited By: Tony Diaz
Deposited On:24 Jun 2013 18:25
Last Modified:09 Nov 2021 23:42

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