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A shallow-focus (3.8?km deep) and low-magnitude (M L 3.8) earthquake occurred near Sheikhupura on August 08, 2010. Shaking was felt in parts of Potwar and northern Punjab but no associated damage has been reported. Tectonically, this earthquake occurred to the south of the Salt Range in the Punjab Seismic Zone (PSZ), a shallow-focus, moderate-level seismic zone characterized by steeply dipping strike-slip and extensional faults. The focal mechanism solution, using the seismological data of the United States Geological Survey and local observatory, shows an EW-trending fault plane dipping 710?N similar to the normal faults reported in the area previously. On the basis of the imposition of the stress field on the northward-moving Indian plate and the nature of the FMS of the previous and this earthquake, the Sheikhupura earthquake is considered as one of the intraplate earthquakes occurring frequently in the PSZ. The location of the event on the Bouguer gravity maps coincides with the zone of high gravity anomaly reflecting igneous intrusion(s) or, more likely, structural disturbances (i.e., extensional faulting in the basement). 相似文献
2.
MonaLisa Azam A. Khwaja M. Qasim Jan Robert S. Yeats Ahmad Hussain Shahid A. Khan 《Journal of Seismology》2009,13(3):339-361
This paper deals with the data obtained from local networks in northern Pakistan for 251 earthquakes of magnitude ≥4.0 for
October 8, 2005 to December 31, 2006 period. The study presents focal mechanism solutions (FMS) of 12 pre- (1904–2005) and
17 post- (October 8, 2005–December, 2005) Muzaffarabad Earthquake, their detailed tectonic interpretation, and correlation
with surface evidence of co-seismic rupture with published synthetic aperture radar data. Distribution of landslides obtained
from National Engineering Services of Pakistan and the earthquake damages are also discussed. Aftershock distribution, which
is more prominent in the crystalline zone (northwest of Muzaffarabad), defines a 50-km-wide NW–SE trending zone that extends
for 200 km from the main mantle thrust to the center of the Hazara–Kashmir Syntaxis. The FMS of the main shock and 16 aftershocks
having magnitude ≥4.0 indicate thrusting to be the dominant mechanism with rupture planes having NW–SE trend and NE dip. In
addition, 12 FMS of pre-Muzaffarabad Earthquake (1904–2004) from the same area have been determined and results are compared.
This leads to the conclusion that the wedge-shaped NW–SE trending blind zone, referred to by earlier workers as the Indus
Kohistan Seismic Zone (IKSZ), has been activated during the Muzaffarabad earthquake. The right-lateral component in all FMS,
supported by the surface evidences, suggests the involvement of Balakot–Bagh Fault (BBF). We propose that the IKSZ is the
source of the October 8, 2005 Muzaffarabad earthquake that reactivated the BBF. Furthermore, the IKSZ does not end at the
nose of the syntaxis but extends further southeast of it. Tectonic complexity seems to be due to a variety of factors. Also,
thrust and reverse solutions near the northern collisional boundary (main mantle thrust) have mostly NE/SW-directed P-axis
orientations. From the detailed FMS analysis, three conclusions have been drawn: (1) Shallow events (depth ≤10 km) with prominent
strike slip solutions (earlier earthquakes) are associated with the surface strike slip faults (e.g., Muzaffarabad Fault)
and/or the Besham domal structure; (2) moderate depth events (depth 10–25 km) with thrust/reverse solutions but having minor
right-lateral strike slip component (all Muzaffarabad earthquakes and two earlier) are associated with the IKSZ; (3) deeper
earthquakes (depth below IKSZ) with pure thrust/reverse solutions may be related to the under-thrusting of the Indian plate
beneath the IKSZ, which represents a major thrust zone. Imbricate thrusting and breaking and thickening of the crust are considered
to be caused by steep bending of the under-thrusting plate at the collisional boundary.
An erratum to this article can be found at 相似文献
3.
Geological setting of the 8 October 2005 Kashmir earthquake 总被引:1,自引:0,他引:1
The source of the 8 October 2005 earthquake of M 7.6 was the northwest-striking Balakot–Bagh (B–B) fault, which had been mapped by the Geological Survey of Pakistan prior
to the earthquake but had not been recognized as active except for a 16-km section near Muzaffarabad. The fault follows the
Indus–Kohistan Seismic Zone (IKSZ); both cut across and locally offset the Hazara–Kashmir Syntaxis defined by the Main Boundary
and Panjal thrusts. The fault has no expression in facies of the Miocene–Pleistocene Siwalik Group but does offset late Pleistocene
terrace surfaces in Pakistan-administered Jammu-Kashmir. Two en-échelon anticlines near Muzaffarabad and Balakot expose Precambrian
Muzaffarabad Limestone and are cut by the B–B fault on their southwest sides, suggesting that folding and exposure of Precambrian
rocks by erosion accompanied Quaternary displacement along the fault. The B–B fault has reverse separation, northeast side
up; uplift of the northeast side accompanied displacement, producing higher topography and steeper stream gradients northeast
of the fault. No surface expression of the B–B fault has been found northwest of the syntaxis, although the IKSZ and steeper
stream gradients continue at least as far as the Indus River, the site of the Pattan earthquake of M 6.2 in 1974. To the southeast, northwest-striking faults were mapped by the Geological Survey of Pakistan. One of these faults,
the Riasi thrust, cuts across the southwest flank of an anticline exposing Precambrian limestone. Farther southeast, in Indian-administered
territory, Holocene activity on the Riasi thrust has been described. In the Kangra reentrant still farther southeast, active
faulting may follow the Soan thrust, along which Holocene and Pleistocene offsets have been described. The Soan thrust, rather
than the south flank of the Janauri anticline, may represent the surface projection of the 1905 Kangra earthquake of M 7.8. 相似文献
4.
An investigation on Balakot, Muzaffarabad (Pakistan) earthquake, 8 Oct. 2005, Mw 7.6; geological aspects and intensity distribution 总被引:1,自引:0,他引:1
In this paper, the investigations on seismotectonic and intensity evaluations of epicentral and meizoseismal regions in Muzaffarabad
earthquake—8 Oct. 2005, Mw 7.6—are summarized using The European Macroseismic Scale (EMS-98). The observations are compiled
based on the field investigations and isoseismal map. The results show that the isoseismals are elongated parallel to the
reactivated Muzaffarabad fault, and the attenuation is high in the direction normal to the fault compared with the direction
parallel to it. The geotechnical investigations in Muzaffarabad Valley have helped the authors to assign intensity values
in the localities where some huge landslides are observed. Finally, the empirical laws, previously developed for intensity
attenuation in Iran in EMS-98 scale, are compared with the intensity observations here. The results are roughly consistent
with the general form of attenuation laws. However, it is found that the intensity attenuations are different in the directions
normal and parallel to the fault. 相似文献
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