Fault based probabilistic seismic hazard assessment at different tectonic regimes and data sampling conditions: emphasis on sensitivity of seismic source characterization

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2019
Shah, Syed Tanvir
Seismogenic sources often display intrinsic complexities; hence they pose a challenge for accurate representation of source geometries and constraining source parameters in seismic hazard assessment. Subduction zone complexities involving megathrust interface, intraslab and accretionary prism faults leads to enhanced uncertainties in seismic source characterization (SSC). Similarly, extensional regimes are often characterized by multiple sets of inclined faults and paucity of individual slip rates; causing considerable ambiguity in activity rate estimation. Moreover, regions characterized by complex tectonics producing mixed earthquake mechanisms lead to challenges in SSC modelling. In this study, detailed seismic hazard analysis with sensitivity tests for various enigmatic parameters is carried out for subduction, extensional and mixed tectonic regimes. For subduction, sensitivity of the hazard outcomes to the alternative magnitude distribution models, dip amounts and interface depth extents is tested. Truncated exponential magnitude distribution model resulted in ~10% higher peak ground accelerations (PGA), when compared to the composite model that has a better match with the seismicity. Gentler and deeper-extending interface geometries resulted in higher PGA values towards the accretionary wedge. For extensional regimes, alternative approaches utilizing geodetic and seismic data are employed to determine the activity rates which are later partitioned among fault systems using morphology and length. Later, a procedure that provides weighted, maximum and minimum PGA maps is established to evaluate and minimize bias on hazard estimates. Finally, polarity data is analyzed to constrain focal mechanism solutions in a regime characterized by mixed strike-slip and normal faulting to constrain the seismic source parameters. The updated planar SSC model that includes an additional areal seismic source to account for off-fault seismicity and complex tectonics, led up to 0.08g increase in hazard.

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Citation Formats
S. T. Shah, “Fault based probabilistic seismic hazard assessment at different tectonic regimes and data sampling conditions: emphasis on sensitivity of seismic source characterization,” Thesis (Ph.D.) -- Graduate School of Natural and Applied Sciences. Geological Engineering., Middle East Technical University, 2019.