Aftershock Ground Motion Record Selection: A Novel Mainshock-Consistent Approach

Abstract

Recent advances in ground motion record selection for mainshock events have highlighted very clearly the critical importance of using record suites consistent with the seismic hazard at the site of interest. Nevertheless, this integral component for analytical derivation of fragility models remains underscrutinized when it comes to aftershock ground motions. Several authors have highlighted the caveats of repeating the same records as both mainshocks and aftershocks, but a conceptually sound methodology for such purposes is still lacking. Herein, we analyze many of the relevant hurdles and challenges involved in selecting ground motion records for aftershocks, and offer a discussion on potential strategies for overcoming them. Finally, we outline a novel procedure that enables a targeted pairing of records from a single database into mainshock-aftershock sequences, while ensuring that they represent realistic scenarios and that they respect the mainshock-aftershock correlation structure.

An extended generalized conditional intensity measure method for aftershock ground motion selection

“…can be determined via the generalized Omori's law, 7 the Bath law, 52 the branching aftershock sequence (BASS) model 53 or the aftershock seismic hazard disaggregation, 44 among others. Such related works are well documented in the literature (e.g., 24,28,29,44,54 ), which provide references for determining the causal parameters of aftershock events. The consideration of all the causal earthquakes for mainshock and aftershock is in the scope of the PSHA and APSHA, respectively.…”

“…It can be seen that the aftershock EGCIM distributions and the unconditional distributions for the six aftershock IMs have a significant difference, which are originated from the correlation relationship between mainshocks and aftershocks as well as the cross-correlations between AS IMs, as computed in Section 3.1. Ignoring these properties is not conducive to generating a precise AS target distribution for aftershock ground motion selection 28,29 and representing the hazards (or site-specific characteristics) and multiple aftershock characteristics of the specific site. One of the advantages of the proposed methodology is that multiple ground motion characteristics and the correlations between mainshocks and aftershocks as well as the cross-correlations between AS IMs can be considered in the aftershock EGCIM distribution, which can be used for aftershock ground motion selection.…”

“…Table 3 lists the different components and weights of the aftershock IM vector. Case 1 of the weight vector represents aftershock ground motions selection results only considering Sa, which has already been used in the existing methods (e.g., 19,28,29 ). Case 2 represents the aftershock selection results considering Sa and Ia.…”

“…Zhu et al 19 proposed a conditional mean spectrum of aftershocks (CMS A ) for aftershock ground motions selection, in which the correlations between mainshocks and aftershocks were considered by the spectral shapes (epsilons) using the copula functions. Papadopoulos et al 27 investigated the statistical correlations between spectral accelerations of MS-AS ground motions, including inter-and intraevent residuals and cross-correlations, then they 28,29 proposed a novel MS-AS sequences selection method using the MS-AS conditional spectrum (MSAS-CS), in which the MSAS-CS conditional on a single mainshock Sa or multiple mainshock spectral accelerations can be generated using the multivariate normal distribution and the developed correlation models. Moreover, numerous studies 7,[30][31][32] have shown that different aftershock selection and synthesis methods could result in notable differences in predicting seismic structural responses.…”

“…19,27 ). Papadopoulos et al 28,29 illustrated the necessity of considering MS-AS correlations in the selection of aftershocks. Therefore, it is necessary to establish a systematic methodology for aftershock selection that considers multiple ground motion characteristics, the correlation between mainshocks and aftershocks, as well as the cross-correlations between AS IMs.…”