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Automated Identification of Teleseismically Recorded Depth
Phases with Application to Improving Subduction Zone
Earthquake Locations
Heather R. DeShon (CERI, Univ. of Memphis), E. Robert Engdahl (Univ. of Colorado-Boulder), Shishay Bisrat (CERI,
Univ. of Memphis), Susan L. Bilek (New Mexico Institute of Technology), Jeremy Pesicek (Univ. of Wisconsin-Madison),
Clifford H. Thurber (Univ. of Wisconsin-Madison)
A large portion of the seismogenic megathrust of most subduction zones lies beneath the ocean, which ultimately limits
the amount of local seismic data available for high precision earthquake location studies. Standard single-event teleseismic
earthquake locations are limited in their ability to provide the level of precision necessary to properly evaluate spatio-temporal
aftershock variability, to constrain subducting plate geometry, or to investigate temporal strain release. Earthquake locations in
global catalogs can be in error by 10's of kilometers in location and depth due to the use of imprecise arrival time picks, phase
misidentification, poor station coverage, etc. Improvements to teleseismic event location, especially in depth, can be accomplished
using more accurate depth phase arrival times. We have developed a new method to identify depth phases (pP, pwP, sP)
and improve P onset times that takes advantage of the high quality IRIS Global Seismic Network waveforms available through
the IRIS Data Management Center. The picker uses abrupt amplitude changes of the power spectral density (PSD) function calculated
at optimized frequencies for each waveform. The technique identifies depth phases not reported in the standard catalogs
and works over a wide-range of depths. The additional depth phases are incorporated with the ISS, ISC, and NEIC phase
catalogs and relocated using the EHB teleseismic location approach [Engdahl et al., 1998]. The automatically identified depth
phases and revised EHB catalogs are being used for two subduction zone studies: 1) Teleseismic double-difference relocation
and tomography along the Andaman-Sunda subduction zone, which takes advantage of the extensive global recordings of the
2004, 2005, and 2007 great (M>8) Sumatra earthquakes [i.e. Pesicek et al., 2010]; 2) A global study characterizing earthquake
source durations in subduction zones, with a focus on identifying unusually slow source processes such as those associated with
tsunami earthquakes [i.e. Bisrat et al., 2009]. To date, we have provided nearly 29,000 new phases to the EHB catalog for ~1250
earthquakes in the Sumatra, Java, Kurile, Japan, Peru, and Alaska subduction zones. Epicentral changes following relocation
using additional depth phases are generally small (