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Development of a Chilean Ground Motion Database for the NGA-Subduction Project


The Next-Generation Attenuation (NGA) projects provide uniformly-processed ground motion data from earthquakes recorded in different tectonic settings and regions around the world. Since 2008, three separate NGA projects have been developed: NGA-West and NGA-West2 for shallow crustal earthquakes in active tectonic regions like California; and NGA-East for stable continental regions like central and eastern North America. Currently, the NGA-Subduction project is under development, focusing on gathering data for regions affected by subduction-zone earthquakes like the Pacific Northwest (PNW) and Alaska regions of North America, Japan, Taiwan, Mexico, and South America, among other areas.

As part of the effort of assembling and characterizing the ground motion dataset for South America, this thesis describes the development of a Chilean ground motion database for the NGA-Subduction project. First, the tectonics and seismicity of South America are discussed to highlight the importance of these subduction-zone earthquakes, with a particular emphasis on Chilean events. Subsequently, an overview of the seismic data providers in Chile is presented, describing the evolution of the different institutions and seismic networks that have recorded ground motions in the country. In addition, prior works on ground motion datasets and ground motion modeling for South America and Chile are introduced and briefly described. The importance of regional considerations in the development of global models, particularly with respect to path terms, is emphasized by comparing attenuation features observed in past work on the 2010 M 8.8 Maule Chile and M 9.0 Tohoku Japan events.

A significant effort was made to collect and characterize required metadata to accompany the ground motion database, including source, path, and site information. This thesis is primarily focused on presenting the development of parameters describing seismic sources. To date, the NGA-Subduction event catalog for the South American region consists of 826 earthquakes that extend from 1985 to 2016, 689 of which have been recorded in Chilean territory. The moment magnitude ranges from M 2.5 to M 8.8. In terms of number of recordings, the data obtained in Chile (4,213 time histories) represents approximately 68% of the total dataset in South America. The event database is controlled by interface and instraslab earthquakes, having 404 and 223 events respectively, with considerably fewer shallow crustal and outer-rise events. When possible, seismic sources are defined using suitable finite fault models (FFM) from the literature. Processes are introduced here to interpret published FFMs in a way that the most salient portion of the fault plane is used for site-to-source distance calculations. These processes improve upon those that had been used previously and have been adopted elsewhere in the NGA-Subduction project (e.g., Japan). In the case of the events without available FFMs, source characterization is similar to that used previously in NGA-projects.

Path and site parameters are currently being characterized and preliminary results are briefly explained in the final chapter. The results presented in this thesis regarding source information, along with the results from path and site characterization, will be part of a data PEER report describing the Chilean dataset.

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