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Crustal Structure from In-Country and Ground-Truth Data
COLORADO UNIV AT BOULDER
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We are investigating the crustal and upper mantle structure of the region in central Asia bounded approximately by longitude 41-67 deg E and latitude 20-44 deg N by using in-country datasets of seismic phase arrival times, supplemented by ground truth datasets developed from our previous research efforts. We present the results of Pn tomography using a dataset consisting entirely of GT5 events in the region. From 27 calibrated earthquake clusters we extract 832 events that qualify as ground truth GT5 at the 90 confidence level. The raypaths of Pn readings from these events provide good coverage of most of the region except for the Makran region in the southeast. To determine an appropriate reference model for the region we compared empirical travel times calculated from the GT5 dataset to those predicted by several models the ak135 global model Kennett et al., 1995, the CUB2.0 model Ritzwoller et al., 2003, and the so-called Unified model a 3-D velocity model of the crust and upper mantle in Eurasia, constructed from models developed by researchers at Lawrence Livermore National Laboratory LLNL and Los Alamos National Laboratory LANL Pasyanos et al, 2004 Begnaud et al., 2004 Steck et al., 2004 Flanagan et al., 2007. Although the CUB2.0 and Unified models do vary laterally, in the study region they vary quite slowly and capture little of the variability of observed travel times. All three models predict Pn travel times that are systematically too fast. These baseline errors range from 2-4 seconds. For this initial round of tomography we stretched the ak135 model to a crustal thickness of 45 km for the reference model.
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