Using high-resolution marine seismic data, marine geophysicists have been able to map the extensive submarine fault system that ruptured during the 8.6 magnitude earthquake that occurred off Sumatra in 2012.
Large intraplate earthquakes generate complex submarine fault systems that can be difficult to differentiate from land-based stations using traditional seismographs.
The complexity of the fault lines has been mapped using marine reflection seismology techniques.
A huge 106-mile fault system was ruptured during the event.
Understanding deep ocean faults in the Sumatran Wharton Basin
The goal was to determine how mechanical forces create strange earthquake activity through study of the distant Wharton Basin off the coast of Sumatra.
Seismic monitors capture shockwaves worldwide, but land-based equipment cannot show structural damage that has been caused to sub-sea floors.
Oceanographers converged aboard research ships in the rift zone where high-resolution seismic reflection maps were developed for many weeks.
Sound waves travelled down into deep sediment deposits to detect structural formations deep below the seabed.
Analysis of these seismic maps indicated significant faulting of the tectonic plates at ancient fault zones.
Physical inspection is not possible, so science has to rely on sound reflection waves.
Identifying intricate strike-slip mechanics at sub-seafloor depths
Strike-slip faulting is usually observed along the plate boundaries, but the 2012 earthquake occurred in an actively deforming zone within the interior oceanic lithosphere.
Tectonic stresses reactivated ancient fracture zones and resulted in the horizontal movement of the rigid plates under enormous mechanical stress.
High-resolution images revealed multi-fault shear zones that caused the destruction of basalt rocks over large submarine channels.
Overlapping faults created an extensive system of secondary fault planes rather than moving along one plane only.
Shear zones absorbed the tectonic strain while releasing massive volumes of energy.
Identification of multi-branched flower structures in the marine reflection data
Imaging of the subsurface revealed a flower-like structure where rising faults branch outward near the upper sediment interface.
Compressional forces led to secondary thrust faults intersecting with main strike-slip shear zones at high angles.
Subsurface branching geometry made it possible to explain the cause for the presence of concurrent fault slippage in the 2012 earthquake owing to intersecting faults.
It is challenging for researchers to visualize micro-faults under acoustic reflection due to their size being under a few feet.
Stress distribution in tectonics within ancient fracture zones
Studies on tectonic forces in the region reveal that distributed deformation across the Indian, Capricorn, and Australian component plates results in huge compressive stresses in the central parts of the Indian Ocean.
This continued compression along a northwest–southeast orientation subjects the fracture zone to massive mechanical energy until failure occurs.
From the seismic studies, we gained knowledge about how stress concentrates at the bends in the fault line, as reported by AGU — Tectonics.
The impedance caused by the bends causes tectonic pull-apart basins and push-up ridges (uplift structures) on the ocean floor.
Knowledge about stress concentration gives insight into intraplate lithospheric deformation.
Seismic hazard modeling for smart assessment of active ocean floor boundaries
Scientists point to the necessity of studying the process of multi-fault ruptures to estimate the risks of earthquakes occurring in oceans in the future.
Tracking tsunami threats requires advancements in computer modeling.
Using new structural maps, experts will find out whether there is a chance of a sudden quake forming in adjacent oceanic blocks.
These threats cannot be ruled out.
Marine geophysical studies will reveal whether there are any other tectonic systems around the globe that pose similar threats due to shifting and fractured faults at the submarine level.
It is impossible to unravel the mysteries of underwater geology without using sophisticated imaging tools; still, ocean floor observation systems need to be significantly improved to enhance seismic hazard assessment and support post-rupture earthquake early warnings.
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