The Zahedan cluster is named for the city of Zahedan in eastern Iran.
The cluster includes three earthquakes with magnitude 6.0-6.3 from the
Sefidabeh sequence in February 1994. The source region is remote,
inhospitable, lightly populated and sparsely instrumented, especially
prior to about 2009. The large 1994 events have no arrival time data
closer than about 500 km and including them slightly (by ~0.5 km)
degrades the quality of the location calibration, but it was judged to
be preferable to retain the abundant teleseismic arrivals these events
contain. The cluster has a larger geographic extent than is optimal in
order to obtain adequate azimuthal coverage for direct calibration, but
the location calibration still depends primarily on only three stations.
Because of the relatively small number of readings and stations used for
direct calibration and the small number of events in the cluster there
is greater than usual potential for location bias even through the fit
to the data is good. On the other hand, the calibrated locations for the
large 1994 events agree closely with the source model based on InSAR
data that was published in Parsons et al. (2006, GJI), unlike the
locations from an uncalibrated relocation using an early version of mloc
that were included in that paper. All events have depth control from
near-source and local-distance readings or teleseismic depth phases.
