The discovery of a conjugate system of faults in the Wharton Basin intraplate deformation zone

Abstract

A conjugate system of faults (shear and reactivated fracture zones) accommodates intraplate deformation in the Wharton Basin.

Complex Faulting and Triggered Rupture During the 2018 MW7.9 Offshore Kodiak, Alaska, Earthquake

“…In addition, seismic reflection and high‐resolution bathymetry have revealed numerous approximately N‐S trending faults (Reece et al, ), which were interpreted as preexisting fractures in the Pacific Plate spreading fabric that have been reactivated as predominately normal plate bending faults by Pacific Plate subduction. This sea floor fabric bears striking resemblance to that imaged in the Wharton Basin region (Singh et al, ).…”

Detailed seismic velocity of the incoming subducting sediments in the 2004 great Sumatra earthquake rupture zone from full waveform inversion of long offset seismic data

“…Due to the large thickness of the sediments, the basal sediments are likely to be subjected to high pressure and may be partially lithified; hence, they might be strengthened prior to accretion [Dean et al, 2010;Gulick et al, 2011;Geersen et al, 2013]. On the other hand, besides the plate bending, this area is located in the actively deforming Wharton Basin, where the incoming plate is also affected by the reactivated fracture zones [e.g., Deplus et al, 1998;Carton et al, 2014;Qin and Singh, 2015;Singh et al, 2017] that hosted several great earthquakes in 2012 ( Figure 1) [e.g., Wei et al, 2013]. Near the top of the basement, a high-amplitude negative polarity reflection packet (HANP) is observed [Dean et al, 2010;Ghosal et al, 2014] and interpreted as a predécollement that slips landward as a seismogenic décollement (a detachment fault at the base of the accretionary prism) [e.g., Dean et al, 2010].…”

“…Geersen et al [] found that the base of the input section prior to subduction at northern Sumatra (<100 km north from our study area) may reach temperatures ≥90°C, which is sufficient to drive basement‐related dehydration and other diagenetic reactions (e.g., clay mineral dehydration such as smectite‐illite, grain assemblage alteration leading to cementation). Furthermore, the reactivated fracture zones F6 and F7 [ Carton et al , ; Singh et al , ] and serpentinized upper mantle [ Qin and Singh , ] are present in this area; they may lead to hydrothermal circulation in the crust and upper mantle providing heat for the smectite‐illite transformation at the base of sediments. This dehydration transformation can supply SiO 2 at higher temperatures (70°C–200°C) [ Kameda et al , ], requiring some silica‐rich succession near the basement [ McNeill et al , ].…”

“…Most of the high-angle normal faults lie below Unit 1, end at the boundary of Unit 1/2 (Figure 4), suggesting that the faults are nearly contemporaneous. These faults are probably related to the Geophysical Research Letters 10.1002/2016GL072175 diffuse deformation in the Wharton Basin [e.g., Geersen et al, 2015;Graindorge et al, 2008;Singh et al, 2017], or due to plate bending, which has also been found~300 km south of our profile [Franke et al, 2008] and in other subdution zones [e.g., Ranero et al, 2003Ranero et al, , 2005. The active fault reaching the seafloor above the bathymetric high structures at the distance~5 km might be related to the reactivation of fracture zone F6 [Singh et al, 2011;Qin and Singh, 2015] or shear zones [Singh et al, 2017].…”

“…These faults are probably related to the Geophysical Research Letters 10.1002/2016GL072175 diffuse deformation in the Wharton Basin [e.g., Geersen et al, 2015;Graindorge et al, 2008;Singh et al, 2017], or due to plate bending, which has also been found~300 km south of our profile [Franke et al, 2008] and in other subdution zones [e.g., Ranero et al, 2003Ranero et al, , 2005. The active fault reaching the seafloor above the bathymetric high structures at the distance~5 km might be related to the reactivation of fracture zone F6 [Singh et al, 2011;Qin and Singh, 2015] or shear zones [Singh et al, 2017]. In the sedimentary layers, there are some bright reflectors in the depth range of 6-7 km that correspond to low-velocity anomalies in the inverted velocity model (Figure 2), which might be related to channels that are caused by the lithology [Han et al, 1986], or fluid accumulation due to the lithification and subsequent dehydration from the deeper layers [e.g., Vrolijk et al, 1991].…”