A 3D Tomographic Model of South Central Asia Based on Pn Travel Times from GT Events

Increasingly, nuclear explosion monitoring is focusing on detection, location, and identification of small events recorded at regional distances. Because Earth structure is highly variable on regional scales, locating events accurately at these distances requires the use of region-specific models to...

Full description

Saved in:
Bibliographic Details
Main Authors: Young, Christopher J, Ballard, Sanford, Hipp, James R, Chang, Marcus C, Barker, Glen T, Begnaud, Michael L, Phillips, W Scott, Steck, Lee K, Rowe, Charlotte A
Format: Report
Language:English
Subjects:
ACCURACY
ASIA
COMPUTATIONS
DETECTION
EARTH CRUST
EARTH MANTLE
EARTH(PLANET)
Explosions
FAR EAST
FOCUSING
FORWARD AREAS
GLOBAL
IDENTIFICATION
MONITORING
NUCLEAR EXPLOSIONS
Nuclear Weapons
RECEIVERS
SCALE
Seismology
SIMPLIFICATION
SOUTH ASIA
SOUTH CENTRAL ASIA
TIBETAN PLATEAU
TRAVEL TIME
VARIABLES
Online Access:Request full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Increasingly, nuclear explosion monitoring is focusing on detection, location, and identification of small events recorded at regional distances. Because Earth structure is highly variable on regional scales, locating events accurately at these distances requires the use of region-specific models to provide accurate travel times. Improved results have been achieved with composites of 1D models and with approximate 3D models with simplified upper mantle structures, but both approaches introduce nonphysical boundaries that are problematic for operational monitoring use. Ultimately, what is needed is a true, seamless 3D model of the Earth. Towards that goal, we have developed a 3D tomographic model of the P velocity of the crust and upper mantle for the region of southcentral Asia centered around the Tibetan Plateau. Our model is derived from almost 140,000 Pn picks for more than 5300 events recorded at 563 stations from a Ground Truth (GT) dataset assembled by Los Alamos National Laboratory (LANL). Our starting model is the a priori model of East Asia developed by LANL, which is based on various global and regional studies. The topmost layers come from the Laske and Masters global sedimentary model from 1997. As our dataset lacks the resolution to improve this sedimentary portion of our model, we fix the velocity and depth of these layers, as well as the depths of the major mantle discontinuities (Moho, 410 km, 660 km). We invert for P velocities from the crust down through the upper mantle, along with source and receiver terms to account for the effects of event mislocation and fine-scale structure near the receiver not accounted for in the crustal model. Forward calculations are made using our own implementation of the Um and Thurber ray pseudo-bending approach (Ballard, 2008, these Proceedings) with full enforcement of Snell's Law in 3D at the major discontinuities. Published in the Proceedings of the 30th Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies, 23-25 Sep 2008, Portsmouth, VA sponsored by the National Nuclear Security Administration (NNSA) and the Air Force Research Laboratory (AFRL). The original document contains color images.