Opzioni
Neo-Deterministic Seismic Hazard Assessment (NDSHA) for Sumatra: application at regional and local scales
IRWANDI, IRWANDI
2016-04-15
Abstract
Standard probabilistic seismic hazard assessment (PSHA) method cannot fill in the knowledge gap in the physical processes behind an earthquake. A more adequate definition of the seismic ground motion can be given by neo-deterministic seismic hazard assessment (NDSHA), which is based on the possibility of efficiently computing realistic synthetic seismograms, that has already been applied in many countries and supported by available observations. Most of the earthquake hazard assessment studies about Sumatra have been based on PSHA and that is why we have decided to apply NDSHA procedure to this region. However, due to the complexity of fault and tectonic settings, with high seismicity and significant, large magnitude, destructive earthquakes, that characterize this region some modifications to the standard implementation are required.
In order to handle the different types of seismogenic zones around Sumatra Island, it is required to enhance the source definition procedure from the standard version of NDSHA to an updated one, which can be used to control the parameters of the seismogenic zones individually, i.e. adopting a different grid resolution for each seismogenic zone. We enhance the source definition procedure by the introduction of several features, such as adapting the source smoothing effect, respect to geometry and magnitude, and enhancing the source depth definition. The strike slip Sumatra fault generates shallow earthquakes overlying the deeper ones, generated by the Sunda subduction zone. We compiled several tomography studies, at regional and global scale (e.g. (Crust 2.0 and Litho 1.0), to construct the structural models, with the related information about density, seismic velocities (Vp, Vs), and seismic attenuation (Qp, Qs).
A parametric test software, producing maps to study the geographical distribution of the ground shaking related to single earthquake scenario, has been improved to handle different structural models related to the several polygons interested by the source-receiver paths. We applied the procedure to study the Takengon earthquake event (July 2, 2013, with magnitude 6.1). We compare the result with the shaking maps produced by USGS. The comparison reveals a relatively similar strong ground motion distribution except for few areas near the epicenter where our computational technique suffers from intrinsic limitations.
NDSHA has been used also at a local scale, considering scenario events, for seismic microzonation purposes. This was performed by an hybrid method to determine also the amplification effects due to the presence of sedimentary layers. We investigate the local site effects at Banda Aceh City and surrounding areas, considering two earthquake scenarios, from subduction and strike slip zones.
Future studies could be devoted to better characterize the structural models, e.g. performing regional surface wave tomography, to improve computational approaches for synthetic seismograms, e.g. including oceanic-continent paths, and to implement more realistic extended source models to deal with mega earthquakes.
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