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[1] The irregularly distributed surface fault-ruptures of the Wenchuan earthquake spanned over 200 km along the Longmen Shan(LMS) fault zone. Through field investigations, we found over 10 coseismic surfaceruptures, with maximum vertical displacements of approximately 6 m on the Yingxiu-Beichuan fault and 2 m on the Guanxian-Anxian fault; however, the entire fault rupture movement was still not clearly understood since high topographic areas were inaccessible. Thus, we used interferometric synthetic aperture radar (InSAR) satellite observations to capture whole coseismic surface-ruptures and crustal deformations across the LMS faults. We created a novel bi-fault-slip model to invert fault-slips using InSAR information which yielded that thrust fault-slips were dominant at YingXiu, Houshenggou and Bajiaomiao in the near-epicenter segment, while the dextral fault-slips were dominant at Pingtong and Nanba along the northeast segment. The combination of field investigations and simulations suggested that the two coseismic fault zones ruptured with an irregular surface distribution accompanied by crustal deformations.

This article summarizes the Next Generation Attenuation (NGA) Subduction (NGA-Sub) project, a major research program to develop a database and ground motion models (GMMs) for subduction regions. A comprehensive database of subduction earthquakes recorded worldwide was developed. The database includes a total of 214,020 individual records from 1,880 subduction events, which is by far the largest database of all the NGA programs. As part of the NGA-Sub program, four GMMs were developed. Three of them are global subduction GMMs with adjustment factors for up to seven worldwide regions: Alaska, Cascadia, Central America and Mexico, Japan, New Zealand, South America, and Taiwan. The fourth GMM is a new Japan-specific model. The GMMs provide median predictions, and the associated aleatory variability, of RotD50 horizontal components of peak ground acceleration, peak ground velocity, and 5%-damped pseudo-spectral acceleration (PSA) at oscillator periods ranging from 0.01 to 10 s. Three GMMs also quantified “within-model” epistemic uncertainty of the median prediction, which is important in regions with sparse ground motion data, such as Cascadia. In addition, a damping scaling model was developed to scale the predicted 5%-damped PSA of horizontal components to other damping ratios ranging from 0.5% to 30%. The NGA-Sub flatfile, which was used for the development of the NGA-Sub GMMs, and the NGA-Sub GMMs coded on various software platforms, have been posted for public use.

We developed an empirical ground-motion model for subduction earthquakes in Japan. The model is based on the extensive, comprehensive subduction database for Japan by the Pacific Earthquake Engineering Research Center. The model predicts the RotD50 horizontal components of peak ground acceleration, peak ground velocity, and 5%-damped elastic pseudo-spectral acceleration ordinates in the selected periods ranging from 0.01 to 10 s. The model includes predictor variables considering tectonic setting (i.e. interplate and intraplate), the hypocentral depths, magnitude scaling, distance attenuation, shallow soil, and the basin responses. The magnitude scaling of interplate earthquakes is well constrained in Japan for different periods because the database includes the well-recorded large-magnitude events (i.e. the 2003 Tokachi-Oki and 2011 Tohoku earthquakes). The developed ground-motion prediction equation covers the subduction earthquakes that occurred in Japan for moment magnitudes ranging from 5.5 to 9.1 with closest distances to the fault of less than 300 km.

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