Fault-based probabilistic seismic hazard assessment of the eastern Makran subduction and the Chaman transform fault, Pakistan: Emphasis on the source characterization of megathrust

Seismic source characterization (SSC) for probabilistic seismic hazard assessment (PSHA) in regions characterized by subduction megathrust involves a considerable ambiguity. Lack of detailed geologic, seismic, and geodetic data increases the uncertainties. The enigma is enhanced in regions where thin-skinned accretionary prism faults are part of active deformation. In this study, a planar SSC model for seismically active eastern Makran subduction zone, its associated accretionary prism faults and Chaman transform fault zone is proposed based on a kinematic block model accounting strain partitioning. Sensitivity tests for various parameters of the SSC model are performed by computing peak ground acceleration (PGA) maps for 475-year return period. Among alternative magnitude distribution models, the truncated exponential model gives ~10% higher PGA values than the composite recurrence model, which is favored by the observed subduction seismicity. Especially in gently dipping subduction zones such as Makran, estimated PGA values and their spatial distribution are highly sensitive (changing up to 0.3 g) to the megathrust interface geometry near the surface, dip amount, and defined depth limits. Gentler and deeper extending subduction interface maximizes the rupture width and results in higher PGA values towards inland, while the inclusion of shallow aseismic portion produces larger PGA values near the trench. Through eastward transition from subduction to transform motion, thrust faults within the Makran accretionary prism bend northward, forming oblique fault systems with higher slip rates and accommodate part of the compression in accordance with the lateral slip rate variations identified on the Chaman transform fault zone. Using the selected SSC model, the PGA values for short return period (475-year) are estimated to be between 0.5 g and 0.7 g within the accretionary prism down to the trench across the Makran subduction and along southern section of Chaman transform fault zone where slip rates are higher relative to the north.
Journal of Asian Earth Sciences


Fault-based Probabilistic Seismic Hazard Assessment of the Makran Subduction Zone and the Chaman Transform Fault in Pakistan: Emphasis on the Effects of Source Characterization of Megathrust
Shah, S Tanvir; Özacar, Atilla Arda; Gülerce, Zeynep (2019-04-07)
Seismic source characterization (SSC) for probabilistic seismic hazard assessment (PSHA) in regions characterized by subduction megathrusts involves a considerable degree of ambiguity due to the complex nature of subducting plates and large seismogenic depths. The lack of detailed geologic, seismic, and geodetic histories increase the uncertainties involved in constraining the parameters of the SSC model. The enigma is further enhanced in the regions where thin skinned accretionary prism faults associated w...
Yücemen, Mehmet Semih (1994-03-01)
Demarcation of areal and linear seismic sources involves a certain degree of uncertainty and this should be reflected in the final seismic hazard results. The uncertainty associated with the description of the geographical coordinates of a source zone boundary is modeled by introducing the concept of 'random boundary', where the location of the boundary is assumed to exhibit a spatial bivariate Gaussian distribution. Here the mean vector denotes the best estimate of location and the variance reflects the ma...
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Yilmaz, Nazan; Yücemen, Mehmet Semih (2015-07-03)
Influence of different models and assumptions with respect to seismic source modelling and magnitude distribution on seismic hazard results is examined, taking Jordan as a case study. Four alternative models, which are based on different combinations of seismic source models and magnitude-recurrence relationships, are considered. Seismic hazard curves obtained at four different sites in Jordan according to these four models are compared. In order to display the magnitude of spatial variation of peak ground ...
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Yılmaz Öztürk, Nazan; Yücemen, Mehmet Semih; Department of Civil Engineering (2008)
Due to the randomness inherent in the occurrence of earthquakes with respect to time, space and magnitude as well as other various sources of uncertainties, seismic hazard assessment should be carried out in a probabilistic manner. Basic steps of probabilistic seismic hazard analysis are the delineation of seismic sources, assessment of the earthquake occurrence characteristics for each seismic source, selection of the appropriate ground motion attenuation relationship and identification of the site charact...
Evaluation of Site Characterizations and Site Effects of the Ankara Basin Turkey
Koçkar, Mustafa Kerem; Akgün, Haluk (2007-06-28)
The purpose of this study is to assess the in-situ site characteristics and to perform seismic hazard studies of the Upper Pliocene to Pleistocene fluvial and Quaternary alluvial and terrace deposits located towards the west of Ankara. Based on a general engineering geological, geotechnical and seismic characterization of the site, site classification systems were assigned for seismic hazard evaluations. Then, short-period noise recordings of the microtremor measurements at the ground surface have been used...
Citation Formats
S. T. Shah, A. A. Özacar, and Z. Gülerce, “Fault-based probabilistic seismic hazard assessment of the eastern Makran subduction and the Chaman transform fault, Pakistan: Emphasis on the source characterization of megathrust,” Journal of Asian Earth Sciences, pp. 0–0, 2021, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/69875.