Hybrid k-squared source model for strong ground motion simulations: Introduction

Common kinematic strong motion modeling techniques can be divided into integral and composite according to the source representation. In the integral approach, we usually consider the rupture propagating in the form of a slip pulse, creating the k-squared final slip distribution. Such a model is acceptable on large scales where the faulting process is assumed to be deterministic, which is also supported by low-frequency slip inversions. Nevertheless, on small scales the real rupture is rather disorganized (chaotic) and requires a stochastic description. This is involved in the composite approach, in which the source acts as a discrete sequence of individually rupturing subevents. However, this model usually leads to incorrect spectral amplitudes in the low-frequency band (as compared to the integral model). The purpose of this study is to propose a hybrid kinematic k-squared source model based on a set of subsources, scaled to provide the k-squared slip distribution. The modeling combines: (1) the integral approach at low frequencies, based on the representation theorem and the k-squared slip distribution (obtained by composing subsources slip contributions), and (2) the composite approach at high frequencies, based on the summation of ground motion contributions from the subsources, treated as individual point sources. The same set of subsources is used in both the approaches, i.e. for both the frequency ranges. The hybrid method is numerically efficient, while minimizing the above-mentioned problems of both the techniques. The source model is applied to two events: 1999 Athens ( M w = 5.9 ) and 1997 Kagoshima ( M w = 6.1 ) earthquake examples. In the first example, the simulated PGAs are examined with respect to the attenuation relation for Greece. In the second example, synthetic velocigrams are compared with observed data showing that, despite the neglected site-effects, the complexities of measured waveforms are relatively well reproduced.