Grid-Search Techniques for Seismic Event Location and Phase Association

Abstract

REPORT DOCUMENTATION PAGEOMB maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services. Directorate for Information , 1215 Jefferson Davis Highway, Suite 1204. Arlington, VA 22202-4302. Respondents shoutd be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY)2. REPORT 14. ABSTRACTThe objectives of this project are to develop improved methods for locating seismic events and to develop new approaches to analyzing the seismic event location uncertainty. Our efforts are focused on the problems of both single and multiple event location. For a single event, we have formulated a statistical approach based on maximum-likelihood estimation and implemented it with grid-search and Monte Carlo techniques to yield an algorithm called "Grid-Search Single Event Location" (GSEL), which computes non-elliptical confidence regions on event locations for a wide class of assumed probability distributions (Gaussian and non-Gaussian) and for data picking errors. We have applied GSEL to regional arrival data from the 1991 Racha earthquake sequence and from the 1998 Adana (Turkey) earthquake sequence. Our multiple-event grid-search location algorithm (called GMEL) is also based on a maximum likelihood formulation of the location problem and it solves jointly for the location parameters (hypocenters and origin times) of seismic events in a cluster and travel-time corrections at the stations recording the events, GMEL accommodates non-Gaussian as well as Gaussian models of picking errors. We test this GMEL with clusters of 1999 Izmit/Duzce (Turkey) earthquake sequence. The approach we developed is based on the maximumlikelihood framework determines confidence regions on event locations under a general class of picking error models (Gaussian and nonGaussian). For a single event, we have formulated a statistical approach based on maximumlikelihood estimation and implemented it with grid-search and Monte Carlo techniques to yield an algorithm called "Grid-Search Single Event Location" (GSEL), which computes non-elliptical confidence regions on event locations for a wide class of assumed probability distributions (Gaussian and non-Gaussian), and for data picking errors. We have applied GSEL to regional arrival data from the 1991 Racha earthquake sequenceand from the 1998 Adana (Turkey) earthquake sequence.Our multiple-event grid search location algorithm (called GMEL) is also based on a maximum-likelihood formulation of the location problem and it solves jointly for the location parameters (hypocenters and origin times) of seismic events in a cluster and travel-time cor...