New calibrated cluster posted to GCCEL:
The Dezhgan cluster is named for the village of Dezhgan in Hormozgan
Province in southern Iran. The cluster includes seismicity at Qeshm
Island in the Strait of Hormuz. The cluster contains many earthquakes
with magnitudes in the range 5.0-5.9, and three larger events, 6.0 mb on
September 10, 2008 (at Qeshm Island) and 6.0 and 6.3 mb on July 1, 2022.
In order to obtain adequate azimuthal coverage for direct calibration it
was necessary to extend the distance limit used for estimating the
hypocentroid to 1.2°, to pick up readings from seismograph stations to
the south, across the Strait of Hormuz, in the UAE. In the distance
range 1.0-1.2° Pn and Sn arrivals are often found following close to the
arrival times of direct crustal phases Pg and Sg. This required careful
inspection of residuals to avoid biasing depth estimates. The data set
includes arrival times from temporary network stations that were
operated on Qeshm Island by Yamini Fard and colleagues from the IIEES,
as well as observations of S-P reported from strong motion stations very
near epicenters on Qeshm Island by Reza Ghods from IASBS. These data
help constrain focal depths and also helped guard against location bias
from unmodeled lateral heterogeneity, which is likely rather strong in
this area.