A Bayesian source model for the 2004 great Sumatra‐Andaman earthquake

Abstract

The 2004 Mw 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.

Extreme scale multi-physics simulations of the tsunamigenic 2004 sumatra megathrust earthquake

“…The modeled slip of 40 m at the trench both near the hypocenter and at 8 • latitude matches the slip distribution most recently inferred by [12], as well as previous inversions [79], and ground motions records of teleseismic broadband arrays [54].…”

“…On KNL, we measured 1002 GFLOPS for Equations (9) and (10) and 968 GFLOPS for Equations (11) and (12). This compares well to the kernel performance shown in Figure 3, which shows that a matrix based formulation with the code generation ansatz delivers high performance almost automatically.…”

“…Our simulated earthquake has M w 9.18, with maximum horizontal displacement reaching 46.5 m near the trench in the two locations that match those determined by [12]. Horizontal and vertical surface displacements match the GPS observations used by [12] extremely well in both magnitude and orientation ( Figure 9).…”

“…Horizontal and vertical surface displacements match the GPS observations used by [12] extremely well in both magnitude and orientation ( Figure 9). Only near the epicenter, where we prescribe artificial nucleation, does the model exceed inferred observations, hinting at a more complex nucleation process than we implement.…”

“…We validate our simulation against the most recent inversion of geodetic and tsunami data [12] that accounts for data uncertainties in a Bayesian framework. Their preferred model has M w 9.25 and returns slip of 40 m at the trench in two locations, near the hypocenter and near 8 • latitude.…”