HYPOCENTER RELOCATION AND COMPOSITE FOCAL MECHANISM STUDIES FOR NORTHERN PAKISTAN
MEE13608
ZAHID Raza
Supervisor: Nobuo HURUKAWA
Country: Pakistan
The
Water and Power Development Authority in Pakistan (WAPDA) has been operating a
seismic network in the northern areas of the country since 2010, in order to
monitor seismicity in the region. To improve the identification of micro
earthquake hypocenter locations, an average VP/VS ratio of 1.73 by plotting a Wadati diagram was obtained. Eight velocity
models were examined using this value of the VP/VS ratio for the same data set. The Tarbela velocity model was found to be
the best among these models considering the hypocenter distribution, the value
of the root mean squared residual (RMS) and the number of zero-depth events.
The crustal thickness of the Tarbela velocity model was modified from 33.5km to
60km considering RMS values for events outside the network. 185 earthquakes of
M ≥ 0.6 reported by WAPDA for the period of 2010-2013 were relocated using the
Modified Joint Hypocenter Determination (MJHD) method. Four groups of
earthquakes were established. The first was along the Punjal Thrust in the
Hazara Kashmir Syntaxes and the second along the Indus Kohistan Seismic Zone
(IKSZ), which is 45 km long and 34km wide trending in a NW-SE direction. The
seismicity for this area is mostly confined to a depth range of 0-30 km,
extending in places to 60 km. Three subgroups were established within the IKSZ
running in a NE-SW direction, which is perpendicular to the main trend of
seismicity. The third group was found to be around the Besham dome. The fourth group was along
the Main Mantle Thrust (MMT). Two deep earthquakes were also located at depths
greater than 250km. Furthermore, earthquake composite focal mechanisms in eight
regions were obtained by using the relocated earthquakes. From these eight
groups, seven thrust mechanisms and one normal mechanism were determined. For
deeper crustal earthquakes (50-100km), a strike slip mechanism with E-W
compression was established.