UCLA

For engineering design and seismic risk assessments, earthquake ground motions are characterized using intensity measures such as peak acceleration or spectral accelerations. Ground motion models (GMMs) estimate statistical distribution of intensity measures given information about the source, source-site path (distance), and site condition. This research pertains to data resources used to develop GMMs for subduction zone regions and adapts a global GMMs to a target region. My initial research developed portions of the NGA-Subduction (NGA-Sub) project database. I worked with other experts to characterize seismic sources and source-to-site paths. The database contains data from 1,880 earthquakes in Alaska, Cascadia, Central America and Mexico, Japan, New Zealand, South America, and Taiwan. Source parameters are related to the earthquake focus and finite fault representations. An important issue was the assignment of event types (intraslab and interface). I developed event type classification procedures that consider hypocenter locations relative to the interface, focal mechanisms, and other factors. The second phase of research involved collaborating with researchers in Mexico to enhance data resources for that region (relative to NGA-Sub) and to use the information to develop a regionally customized GMM. I selected Mexico because it has high seismic hazard, its available GMMs have deficiencies, and it has substantial data from recent events that were not considered in NGA-Sub. The database for Mexico is extended by considering small magnitude (M < 6) events and three large events (M 7.2-8.3) in 2017 and 2018. The latter are particularly important, because they are well recorded over a broad distance range and apply for hazard-critical conditions. These changes increase the size of the database from 593 recordings from 66 events (NGA-Sub) to 1882 recordings from 121 events. These data are examined relative to a global NGA-Sub model, which reveals a number of interesting features including faster anelastic attenuation in backarc than forearc regions and generally similar levels of site response as in the global GMM. A novel model for site response in Mexico City is proposed that is properly centered with respect to GMMs and that accounts for the unique Lake Texcoco geology.