Interpretation of Earthquake Epicenter and CMT Centroid Locations, in Terms
of Rupture Length and Direction
Gideon P. Smith1, and Göran Ekström
Department of Earth and Planetary Sciences, Harvard University,
Cambridge, MA, USA.
1Now at Department of Earth and Planetary Sciences,
Washington Univ., St. Louis, MO, USA
Phys. Earth and Plan. Int., 102, 123-132, 1997.
Abstract
A comparison is made between hypocenter and centroid estimates of shallow
earthquakes to investigate whether the difference between these two quantities
contains useful information on fault rupture length and direction. An initial
comparison of ISC and Harvard CMT catalogue locations suggests that for
earthquakes below MW > 6.5 the difference in location is dominated by location
errors, whilst larger earthquakes appear to show the effect of increasing
spatial rupture. However, for this data set combined location errors greater
than 25 km are observed for a majority of earthquakes imposing a limit
on interpretation. We use these constraints to investigate this approach
using a consistent Earth model in the re-analysis of 8, previously well-studied,
events. New hypocenter estimates based on teleseismic P-wave arrivals from
the ISC Bulletin, and a 3-D velocity model of the mantle (S&P12/WM13)
are compared to new centroid locations obtained using the same 3-D model,
and waveform data from IDA, GDSN, and re-calibrated HGLP stations. The
distance between our new hypocenter and centroid locations is shown to
provide reliable information on both the rupture length and direction.
The rupture lengths and azimuths generally agree with the most recent,
previous results from other methods and provide an absolute estimate of
the location of the rupture.
This Figure shows the match between 6 initial rupture vectors inferred
in this study (white arrows) and those from previous studies (black arrows).
Each arrows base is at the travel-time location and are proportional in
length to each other.