Abstract:
The seismic hazard study for Northern Pakistan has been conducted by using a probabilistic approach in terms of peak ground acceleration (PGA) in units of g. Seismicity hazard was performed to delineate areas of potential landslides and higher ground motion. Probabilistic earthquake recurrence model for earthquakes of 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, and 7.5 Mw were generated for all zones. Seismicity of study area was modeled, and ground motion was computed for 10 frequencies (0.01, 0.05, 0.15, 0.3, 0.5, 0.75, 1.0, 1.5, 2.0, 3.0 s) for different annual exceedance rates of 0.02, 0.01, 0.005, 0.002 and 0.001 (return periods 50, 100, 200, 500 and 1,000 years) for 50 years were generated on the grid of 0.1°. Analytical Hierarchal Process which divides the area into zones of least, moderate, high and extremely high susceptible landslide zones. Boore & Atkinson 2008 for active shallow crustal and Young’s 1997 for subduction region are used, and parameterization is based on most recent updated earthquake catalogs that consisted of 14,000 events which were Declustered using Gardner and Knopf 1978 method, and 2600 events were finally obtained which we used in the study. The threshold magnitude was fixed at Mw 4.0 and 14 seismic source zones were created throughout the study area based on the uniformity of Earthquake Magnitudes and Fault alignment. The average normalized ‘a’ and ‘b’ values for all zones are computed. Seismic hazard maps based on computed PGA showed higher ground motion values for Abbottabad, Muzaffarabad, Mansehra, Battagram, Besham and Dasu ranging from 0.55 to 0.66g, also we have higher precipitation from 800mm – 1234mm, moderate slopes to steep slopes, loose lithology mostly alluvium and sheared strata, positive curvature values, and urban settlements are present in these areas which also added them to more hazard-prone region. These maps indicate the earthquake hazard of Northern Pakistan and surrounding areas in the form of acceleration contour lines, which are in agreement with geological and seismo-tectonic characteristics of the study area. Landslide susceptibility mapping was done using quantitative index-based technique Areas of Besham, Battagram and Mansehra are marked with extremely high susceptibility of landslides triggered due to ground motion and other contributing factors.
