Improved Ground Truth in Southern Asia Using In-Country Data, Analyst Waveform Review, and Advanced Algorithms

• Main Authors: Engdahl, Eric R, Bergman, Eric A, Myers, Stephen C, Ryall, Floriana
• Format: Report
• Language: English
• Subjects: ALGORITHMS; DATA BASES; EARTHQUAKES; POSITION(LOCATION); Seismology; SOUTH ASIA; SURFACE TRUTH; SYMPOSIA; WAVEFORMS

This research has the goal of developing in-country data sets that can be used to improve ground-based monitoring capabilities in southern Asia, in particular the region bounded by 20-44 deg N and 41-67 deg E, by providing information needed to develop and test more accurate travel time models for seismic phases that propagate in the crust and upper mantle. We have also incorporated phase picks from an experienced analyst who reviewed waveforms of particular interest for specific events. These in-country arrival times and analyst-reviewed picks have been associated with known earthquakes reported by international agencies, combined with existing bulletin readings, and relocated using the catalog EHB (Engdahl et al., 1998) methodology. Using in-country data we have formed new events, mostly at lower magnitudes that were not previously included in standard global earthquake catalogs. This has resulted in a catalog of earthquakes in the region for the period 1918-2006 for events larger than about magnitude 2.5. Catalog events larger than about magnitude 4.0 and well-constrained teleseismically have been highly reviewed. Events at lower magnitudes have been relocated with a standard procedure similar to the EHB procedure, but not all systematically reviewed. The new catalog has been used to conduct detailed analysis of historic and recently occurring event clusters (often mainshock-aftershock sequences) using a multiple-event relocation technique and data sets of phase arrival times at distances from near-source to teleseimic. Absolute locations of such clusters are constrained using reference event information for one or more of the cluster events provided by local networks, aftershock deployments, or from non-seismic information such as interferomic synthetic aperture radar (InSAR) or geological mapping. Presented at the Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies (29th) held in Denver, CO on 25-27 Sep 2007. Published in Proceedings of the Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies (29th), p395-405, Sep 2007. The original document contains color images.