Deterministic earthquake scenario simulations are playing an increasingly important role in seismic hazard and risk estimation. The numerical calculation of the complete 3D wavefield in the observed frequency band for a seismically active basin remains a computationally expensive task. This expense restricts seismologists either to calculating source models with homogeneous media (e.g., Gallovic and Brokesoová, 2004, 2007a,b), or to calculating single source scenario in 3D media (e.g., Olsen and Archuleta, 1996; Olsen, 2000; Ewald et al., 2006) while the complex effects of the media and the source on the ground motion are getting more and more attention. At the same time, with the development of the instrument, ground rotation introduced by an earthquake becomes a more and more important topic. Our aim is to provide a tool with which we can calculate a large number of different finite-source scenarios for a particular fault or fault system located in a 3D structure which will enable us to estimate ground motion (translation and rotation) variations due to source and 3D structure. In order to avoid having to run numerical expensive 3D code for each kinematic source scenario we propose the concept of “numerical Green’s functions” (NGF): a large seismic fault is divided into sub-faults of appropriate size for which synthetic Green’s functions at the surface of the seismically active area 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 demonstrate the functionalities of the method a strike-slip NGF data base was calculated for a simplified vertical model of the Newport-Inglewood fault in the Los Angeles basin. As a first example, we use the data base to estimate variations of surface ground motion (e.g., peak ground velocity (PGV)) due to hypocentre location for a given final slip distribution. The results show a complex behavior, with dependence of absolute PGV and its variation on asperity location, directivity effect and local under-surface structure. Hypocentral depth may affect peak ground velocity in a positive or negative way depending on the distance from the fault and the receiver location with respect to basin structure.

Finite-fault source inversions reveal the spatial complexity of earthquake slip over the fault plane. In this study, several possible earthquake scenarios of Mw 7.0 are simulated with different quasi-dynamic finite source models for the Newport-Inglewood fault in the Los Angeles basin. We investigate the effects of the various slip histories on peak ground velocities and the related variations in ground motion prediction for our study area. The results confirm that the fault perpendicular components of motion are dominated by directivity effects while the fault parallel component is influenced both by the slip distribution and the basin structure. There are theoretical considerations suggesting that observations/calculations of the rotation part of earthquake-induced ground motions may provide additional information for earthquake risk hazard analysis after reports on rotational effects on structures (like twisting of tombstones or statues). For the first time, we carry out a systematic study of earthquake scenario simulations in 3D media with a specific focus on the rotational part of the motions. We simulate several M7 earthquakes with various hypocentre locations and slip histories on the Newport-Inglewood fault embedded in the 3D Los Angeles Basin. We investigate source

and basin structure effects on the rotational components of ground motion (e.g., peak ground rotation rates and their variation, horizontal gradients) and compare with the effects on translations.

Igel et al. (2005) shows a similarity of the observed waveforms between transverse acceleration and the vertical rotation rate in the teleseismic range benefiting from the recently developed ring laser instruments. The vertica