Marine Investigation of the Rupture Anatomy of the 2012 Great Earthquake (MIRAGE)

The magnitude-8.6 2012 Wharton Basin earthquake was the largest intraplate earthquake ever recorded in an ocean. Even with modern instrumentation, the anatomy of the rupture of this earthquake remains a matter of debate. In order to fully understand the rupture pattern and faults involved in this great earthquake, we plan to acquire a suite of marine geophysical datasets, including seismic reflection, bathymetry, 3.5 kHz etc. The first phase of Marine Investigation of the Rupture Anatomy of the 2012 Great Earthquake (MIRAGE) expedition took place in July 2016, and the second phase is scheduled to take place in 2017.

During the MEGA-TERA expedition in 2015, the team took high-resolution bathymetric and seismic reflection data, from which we discovered the fracture zone of the magnitude-8.2 aftershock that followed the magnitude-8.6 earthquake. Here, four fracture zones that were reactivated by the 8.6-magnitude Wharton Basin earthquake are shown.

Interpreted seismic reflection image across re-activated fracture zones: Seismic reflection along profile WB03 crossing through four reactivated fracture zones (F6a, F6b, 7a, 7b). Prominent sedimentary horizons are marked in green. The yellow line marks the top of the pelagic sediments. The red curve marks the top of oceanic basement. Thick black lines: major faults; Thin black lines: minor faults; dashed thin black lines link faults imaged in the sediments with deep-rooted strike-slip faults. (Source: Singh et al., Science Advances, 2017)

 

New bathymetry: (a) Interpreted bathymetry. F6a-F7b: reactivated fracture zones. Different symbols are defined in the right-hand upper corner. (a) Simplified interpreted bathymetry showing main features. The insert shows schematic shear zone scheme. (Source: Singh et al., Science Advances, 2017)

The 2012 earthquakes and rupture models: (a) The epicenter of the 2012 great earthquakes (blue and white beach balls) and different fault models (red, yellow and black lines) for the Mw=8.6 earthquake. NER: Ninety-East Ridge. The light pink box indicates the area studied during the MegaTera Experiment in 2015 using the Schmidt Ocean Institute Research Vessel Falkor. (b) New model based on the MegaTera data. Black lines indicate segment of faults along reactivated fracture zones and blue lines that along the newly discovered shear zones (Singh et al., 2017). The Red arrows indicate the diction of maximum compression and green arrows indicate the extension direction for the shear zones (blue). The blue shear zones and black re-activated fracture zones from a set of conjugate system of faults. (Source: Singh et al., Science Advances, 2017)

The vertical cumulative offset on F6b: Interpreted seismic image across F6b along profile WB03 (left) and the cumulative offset as a function of depth across two branches of F6b (F6b1 and F6b2), and as a function of age up to 40 Ma. F6b1 and F6b2 are two branches of re-activated fracture zone F6b (right). Horizontal color lines indicate horizons used in B. Black thin lines indicate interpreted faults in the sediments and the thick solid black line indicates the possible position of shear zone at depth. (Singh et al., Science Advances, 2017)

 

Findings from the study have been published in Science Advances; you may read them here.

A related blog post on these findings may be found here.

Funding Sources: 

  • Earth Observatory of Singapore

Project Years: 

2016
2017
2018
2019

EOS Team: 

Principal Investigator
Collaborator
Collaborator
Collaborator

Collaborators: 

Co-PI:

Paul Tapponnier, China Earthquake Administration

Collaborator(s):

Nugroho Hananto, LIPI

Helene Carton, Institut de Physique du Globe de Paris