Source-related variations of ground motions in 3-D media: application to the Newport-Inglewood fault, Los Angeles Basin

Abstract

SUMMARY Deterministic earthquake scenario simulations are playing an increasingly important role in seismic hazard and risk estimation. Our aim is to calculate a substantial number of different finite-source scenarios, embedded in a 3-D structure for a particular fault or fault system, by pre-calculating numerical Green’s functions (NGFs). A large seismic fault is divided into subfaults of appropriate size for which synthetic Green’s functions at the surface are calculated and stored. Consequently, ground motions from arbitrary kinematic sources can be simulated for the whole fault or parts of it, by superposition. To illustrate this approach and its functionalities we simulate M 7 (up to 0.5 Hz) scenario earthquakes for a simplified model of the Newport-Inglewood (NI) fault in the Los Angeles (LA) Basin. We quantify the variations of surface ground motion (e.g. peak ground velocity PGV and synthetic seismograms) due to source parameters (e.g. hypocentre location and corresponding slip history). The results show a complex behaviour, with dependence of absolute PGV and its variation on asperity location, source directionality and local structure and demonstrate the necessity to combine 3-D structural and finite-source effects to quantify ground motion characteristics and their variations.