Bulletin of the Seismological Society of America; June 2000; v. 90; no. 3;
p. 775-780; DOI: 10.1785/0119990095
© 2000 Seismological Society of America
Improved Relative Locations of Clustered Earthquakes Using Constrained Multiple Event Location
Michael Fehler,
W. Scott Phillips,
Leigh House,
R. H. Jones,
Richard Aster and
Charlotte Rowe
Los Alamos Seismic Research Center
Los Alamos National
Laboratory
Los Alamos, NM 87545
(M. F., W. S. P., L. H.)
ABB Offshore Systems
Penryn, Cornwall, U.K.
(R. H.
J.)
Department of Earth and Environmental Science and Research
Center
New Mexico Tech
Socorro, NM 87801
(R. A., C. R.)
A new method for improving relative locations of clustered earthquakes is
presented and applied to a suite of microearthquakes induced by hydraulic
fracturing. The method is based on the assumption that clustering of
earthquake hypocenters is obscured by the uncorrelated scatter of individual
hypocenters. The method is implemented as an additional constraint in a Joint
Hypocenter Determination (JHD) scheme. The method shifts event hypocenters
toward the center of mass of the events within some volume surrounding the
event location if the RMS misfit between predicted and measured arrival times
does not increase significantly. The method uses the same basic assumption of
Jones and Stewart (1997),
which is that there is greater clustering in actual earthquake locations than
there is in locations determined using conventional techniques. Our method
differs in that it is implemented as part of the JHD process so it operates on
raw travel-time data rather than on derived hypocenters. The method produces
hypocenters from a demonstration field dataset that are similar to those
obtained by Phillips et al.
(1997), from time-consuming
precise manual repicking of relative arrival times of events. The clustering
constraint can easily be incorporated as an additional constraint in
earthquake location/velocity tomography codes and may lead to improved
velocity structure determination and earthquake location pattern
identification and interpretation.
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