Seismicity distribution and focal mechanism solution of major earthquakes of northern Pakistan

Abstract

Pakistan is situated very close to the subduction zone of Indian-Arabian plates and Indian-Eurasian plates. Thus, it is a country with moderate to high seismicity with a large number of major earthquakes. Therefore, the severity of seismic hazards of major earthquakes is not ignorable. The seismicity of northern areas of Pakistan (33-37°N and 70-76°E), which are the part of North West Himalaya, is studied. Three earthquake catalogues are selected and then completed for this purpose. The spatial distribution of their epicenters, as a function of depth, shows that most of the earthquakes (about 84 %) occurred in shallow to intermediate depths. Relationship between major faults and their source mechanism is also investigated. The Focal mechanism solutions of 39 significant earthquakes in this area, occurred in the period of 1976-2014 with magnitude M w [ 5.0, are also analyzed. The focal depth of these events is in the range of 10-244 km. Among 39 focal mechanisms, the majority of them located in lower crust. Global centroid moment tensor solutions indicate that the majority of the seismic events show strike-slip faulting with a left-lateral sense of motion, followed by thrust and normal faulting. Most of these focal mechanisms located in the HinduKush, a most seismically active, region. The major source of these events and thrusting is the subduction of the Indian plate under the Eurasian Plate. At shallow to intermediate depth, low-to-intermediate angle thrust faulting is dominant. It is seen that in a large number of seismic events the compressive stress is acting nearly in NNW-SSE to N-S directions.

Moment Tensor Components with Their Corresponding Eigen Values and Eigen Vectors for Earthquakes Mw ≥ 6.0 in Northern and Southwestern of Pakistan

“…Pakistan is located on the dynamic seismic belt where folds and faults have been observed due to the intra-plate collision between the Indian and Eurasian plates (Kazmi & Jan, 1997;Khalid et al, 2016). These plates are continuously moving towards north at the speed of 15 to 20 cm/year (Patriat & Achache, 1984;Scotese et al, 1988).…”

“…The seismic energy accumulates into the earth's crust and released from faults during an earthquake. Stress analysis and fault plane solution (Presti et al, 2013;Khalid et al, 2016) are tools in practice to analyze the orientation and geometry of the earthquake related features. The fault plane solution describes by the first P wave motion from the nearest station and remaining far stations measure the solution using waveform analysis (Pondrelli et al, 2006;Scognamiglio et al, 2009).…”