Controls on spatial and temporal evolution of prism faulting and relationships to plate boundary slip offshore north‐central Sumatra

Abstract

Across-and along-strike variations in the morphology and structure of the north-central Sumatran forearc (~1.5°S to 1°N) are broadly coincident with subducting plate topography and an earthquake segment boundary zone below the Batu Islands. We present a detailed interpretation of multichannel streamer seismic reflection data collected offshore north-central Sumatra, to better characterize the morphological and structural variations, provide insight into fault development, and relate structure to plate boundary rupture and seismicity patterns. We interpret two relatively continuous, major fault structures that divide the prism into three strike-parallel belts that can be characterized by the relative fault slip rates along major and minor fault structures. The midslope break fault(s) and upper slope-bounding fault(s) are major, potentially out-of-sequence thrusts accommodating a significant component of the compressional strain. We propose that the upper slope-bounding fault represents the more mature end-member of an evolving fault system. Landward vergent structures are associated with a relatively thin sedimentary section near the deformation front in the center of our study area and suggest a potentially weak shallow plate boundary associated with the subducting Wharton Fossil Ridge.

Stratigraphic Control of Frontal Décollement Level and Structural Vergence and Implications for Tsunamigenic Earthquake Hazard in Sumatra, Indonesia

“…Ramp anticlines are separated by 2–3 km, with anticlinal crests sloping toward the trench. This style of deformation is similar to that observed by Cook et al () ~300 km northwest of our study area, where thin sediments overlying the subducting Wharton Fossil Ridge are also imbricated with systematic landward vergence.…”

Downgoing plate topography stopped rupture in the A.D. 2005 Sumatra earthquake

“…DR1). In several places, reflections from prism faults merge at depth with the oceanic basement reflection (Cook et al, 2014). From this relationship and the downdip continuity, we interpret that the décollement is at the top of basement.…”

“…Beneath the accretionary prism a more complex pattern of positive and negative residuals shows lateral density changes. Three regions of positive residual gravity are present beneath the accretionary prism: (1) offshore Nias, positive residuals correspond to an area of active uplift (Cook et al, 2014); (2) offshore the Batu Islands, a series of positive residuals are immediately adjacent to the location of the extinct WFR (Liu et al, 1983); and (3) offshore Siberut, positive residuals align with fracture zones in the subducting plate.…”

Insight Into Frontal Seismogenic Zone in the Mentawai Locked Region From Seismic Full Waveform Inversion of Ultralong Offset Streamer Data

“…Previous studies show that the accretionary wedge offshore the central Sumatra can be divided into three strike‐parallel belts: the frontal prism, midslope break, and terrace (Cook et al, ). In our result, from the top of the BT4 (at ~20 km, Figure ) to further NE, the topography changes on a larger scale than within the accretionary prism toe.…”