Seismic Evidence for Fluid/Gas Beneath the Mentawai Fore‐Arc Basin, Central Sumatra

Abstract

Since 2004, there have been three great interplate earthquakes (Mw > 8.0) offshore Sumatra. In addition to rupturing the megathrust, these earthquakes might also have ruptured the backthrusts that bound the Andaman Islands to the Mentawai Islands toward the forearc basins. Here we apply a combination of traveltime tomography and seismic full waveform inversion to an ultralong offset seismic reflection profile from the Mentawai forearc basin, in the region of the 2007 Mw 8.4 Bengkulu earthquake. We perform a waveform inversion of far‐offset data followed by a waveform inversion of near‐offset data using the starting model derived from the traveltime tomography. Our results show the presence of a large, low‐velocity anomaly above the backthrust. The seismic reflection image indicates that this low‐velocity anomaly lies either within highly compacted sediments from the accretionary wedge or within highly deformed sediments from the forearc basin. The porosity estimation, using the effective medium theory, suggests that a small amount of gas (from 2 to 13%) or a significant amount of fluid (from 17 to 40%) could generate this low‐velocity zone. The presence of fluids and the observation of bottom simulating reflector below a push‐up ridge might be associated with mud diapirism. The fluids could originate locally from the dewatering of the sediments from the accretionary wedge or forearc basin. The high reflectivity of the backthrust in this region might also indicate deeper fluid origin, either from underplated sediments on the subduction interface or from the serpentinized mantle wedge.

A New Method to Estimate Slab Dip Direction Using Receiver Functions and Its Application in Revealing Slab Geometry and a Diffuse Plate Boundary Beneath Sumatra

“…Thus, both earthquake location and passive-source tomography cannot present the slab with high resolution. Several 2D marine active-source surveys have imaged the slab morphology at higher resolutions (Cook et al, 2014;Huot & Singh, 2018;Qin & Singh, 2018;Singh et al, 2008Singh et al, , 2012Singh, Carton, et al, 2011). However, these active-source models are sparse.…”

Hydrothermal Models Constrained by Fine‐Scale Seismic Velocities Confirm Hydrothermal Cooling of 7–63 Ma South Atlantic Crust

“…FWI is an inversion method for seismic data commonly used to recover high‐resolution seismic velocity models of the subsurface and has been used to image upper oceanic crust in a variety of tectonic settings (Arnulf et al., 2014; Christeson et al., 2012; Huot & Singh, 2018; Morgan et al., 2011; Qin & Singh, 2017). In theory, the true physics of seismic waves propagating in the subsurface involve elasticity, anisotropy, density, and attenuation in three dimensions.…”

Seismic wavefield imaging of Earth’s interior across scales

“…FWI is computationally and algorithmically demanding, and, although these demands hampered progress for many decades, these restrictions have been largely overcome in the past decade, due to advances in algorithms and computing technology. Today, FWI is widely used in applications including medical imaging [10][11][12][13][14] , nondestructive testing [15][16][17][18][19][20][21][22][23][24] , near-surface characterization [25][26][27][28][29][30] , onshore and offshore exploration seismology [31][32][33][34][35][36][37][38][39] , deep crustal seismic imaging [40][41][42][43][44][45][46][47] , earthquake seismology [48][49][50][51][52][53][54] and ambient-noise seismology 55,56 . A comprehensive ove...…”

“…Applications of seismic FWI can be categorized as controlled-source, earthquake and ambient-noise seismology. In addition to hydrocarbon exploration and deep crustal imaging [40][41][42][43][44][45][46][47] , controlled-source applications can be further subdivided by scale into medical imaging [10][11][12][13][14] , nondestructive testing [15][16][17][18][19][20][21][22][23][24] and near-surface charac terization of the top tens of metres of the Earth [25][26][27][28][29][30] , but these are beyond the scope of this Technical Review. Since 2010, ambient-noise FWI based on seismic interferometry [159][160][161] has emerged 55,56 .…”