A Bayesian source model for the 2004 great Sumatra-Andaman earthquake
The 2004 M_w 9.1–9.3 Sumatra-Andaman earthquake is one of the largest earthquakes of the modern instrumental era. Despite considerable efforts to analyze this event, the different available observations have proven difficult to reconcile in a single finite-fault slip model. In particular, the critical near-field geodetic records contain variable and significant postseismic signal (between 2 weeks' and 2 months' worth), while the satellite altimetry records of the associated tsunami are affected by various sources of uncertainties (e.g., source rupture velocity and mesoscale oceanic currents). In this study, we investigate the quasi-static slip distribution of the Sumatra-Andaman earthquake by carefully accounting for the different sources of uncertainties in the joint inversion of available geodetic and tsunami data. To this end, we use nondiagonal covariance matrices reflecting both observational and modeling uncertainties in a fully Bayesian inversion framework. Modeling errors can be particularly large for great earthquakes. Here we consider a layered spherical Earth for the static displacement field, nonhydrostatic equations for the tsunami, and a 3-D megathrust interface geometry to alleviate some of the potential epistemic uncertainties. The Bayesian framework then enables us to derive families of possible models compatible with the unevenly distributed and sometimes ambiguous measurements. We infer two regions of high fault slip at 3°N–4°N and 7°N–8°N with amplitudes that likely reach values as large as 40 m and possibly larger. These values are a factor of 2 larger than typically found in previous studies—potentially an outcome of commonly assumed forms of regularization. Finally, we find that fault rupture very likely involved shallow slip. Within the resolution provided by the existing data, we cannot rule out the possibility that fault rupture reached the trench.
Additional Information© 2016 American Geophysical Union. Received 11 FEB 2016; Accepted 22 JUN 2016; Accepted article online 5 JUL 2016; Published online 16 JUL 2016. This work was granted access to the HPC and visualization resources of Centre de Calcul Interactif hosted by Université Nice Sophia Antipolis and of the CITerra/FRAM cluster hosted by the California Institute of Technology. The study was partly supported by the French National Research Agency (ANR) EPOST project ANR-14-CE03-0002, the French Ministry of Research and Higher Education, the Université Nice Sophia Antipolis, the Centre National de la Recherche Scientifique (CNRS), and the California Institute of Technology. We are grateful to Y. Yamazaki and F. Pollitz for providing their respective codes NEOWAVE and STATIC1D, to H. Yao for providing material used in Figure 8, and to Z. Duputel, L. Rivera, J.-M. Nocquet, and B. Delouis as well as L. Feng, Y. Ben Zion, and an anonymous reviewer for their valuable comments. The ISC seismicity catalog shown in Figure 7 is available online (www.isc.ac.uk).
Supplemental Material - jgrb51682-sup-0001-supinfo.pdf