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Group A, Poster #213, Computational Science (CS)

Numerical modeling of ground surface rupture in large thrust and reverse fault earthquakes: An example from the Cucamonga fault, southern California

Kristen Chiama, Robb Moss, James F. Dolan, & John H. Shaw
Poster Image: 

Poster Presentation

2023 SCEC Annual Meeting, Poster #213, SCEC Contribution #12816 VIEW PDF
We aim to develop a mechanical basis for understanding ground surface deformation that occurs during large thrust and reverse fault earthquakes, with a particular emphasis on past and future events in southern California. Active thrust faults pose significant earthquake hazards in California and in many other plate boundaries around the world. Events such as the 1952 Kern County (M7.3), 1971 San Fernando (M6.7), and 2008 Wenchuan (M7.9), China earthquakes demonstrate the complex nature of these ruptures, which often exhibit significant components of distributed fracturing, folding, and faulting that pose specific hazards in urban environments. Such hazards can also impact critical informatio...n and energy transmission infrastructure, transportation systems, as well as other sensitive facilities.

We use geomechanical models based on the distinct element method (DEM) to describe Holocene ground surface rupture of the Cucamonga fault as recorded in a paleoseismic trench excavated by Dolan et al. (1996) on the Day Canyon alluvial fan. The trench shows at least two, and likely at least three rupture events in the last ~7,000 years on a ~31ยบ N-dipping fault zone with ~2.0 or 3.0 m of slip in each event. We evaluate a range of model parameters such as the fault dip, sediment depth, and sediment strength mechanics to reproduce the observed surface deformation characteristics including the deformation zone width, uplift, and scarp dip angle. Our analysis shows that such models can help refine the assessment of earthquake source characteristics, including fault dip at depth and slip in each event.

We propose that our geomechanical models offer the ability to forecast the characteristics of potential future ground surface ruptures and offer new insights into paleoseismic trench analysis that can improve seismic hazard assessment.