“The quality of the data is great,” announces Dr. Singh at the daily morning meeting on R/V Falkor’s bridge. For days, the ship has been navigating slowly, at just over 4 knots, while meticulously obtaining detailed imagery of an enigmatic portion of the Wharton Basin’s floor. This exercise translates into more than 530 Km of seismic reflection profiles and over 5250 Km2 of high-resolution bathymetry.
Bathymetric data acquired in real time gives the scientific team invaluable insight on where to focus their efforts. At first, the success was moderate: faults appeared where the experts expected them to be, therefore taking them closer to proving their theories. But now those clues have guided them further, in unexpected directions, and active features such as faults or gas chimneys have been identified.
A Mirage
“You think you can see it clearly, but as you come closer it’s either not there or it’s something different,” Dr. Singh says, referring the mysterious quality of this area. No one has been able to decipher, let alone prove, why the lithosphere of the Wharton Basin would rupture the way it did in a complex magnitude 8.6 strike-slip earthquake. The theories presented to explain the 2012 earthquake have all been like a mirage – possible from afar, but disappearing when carefully examined.
“Seismological studies have shown that the magnitude 8.6 earthquake rupture was complex, possibly involving multiple segments of a near-orthogonal conjugate network of faults,” points out Dr. Hélène Carton. This means the Wharton Basin’s floor may have ruptured in several perpendicular directions. The problem, she declares, is that there is no field evidence of such orthogonal faults, and experts are not even sure that faults can really spread like that.
Seismological and geodetic data have led to different conflicting models of the earthquake rupture. “The Earth is not a cake, you can’t just cut it however you like!” declares Dr. Singh. The mystery is not just about the earthquakes themselves, but also about the resulting oceanic crust deformation.
A Basin Within the Basin
No one saw it coming. No one thought that the 2004 Indian Ocean earthquake would cause such devastation. Likewise, no one believed that a magnitude 8.6 strike-slip earthquake could originate in the interior of a plate. A magnitude 8.2 aftershock was also unprecedented.
And yet there it is, a small basin on the ocean floor: A clear signature of strike-slip deformation. Pull-apart basins are formed when blocks of lithosphere rub against each other and drift apart. This particular basin sits along a re-activated fracture zone that might have ruptured during the 2012 great earthquake.
Our planet’s crust shows the stretch marks left by its cooling, traces left for us to explore on its skin. More that 4Km below the sea surface, this record is 70 meters deep, 2Km wide and stretches for 5,4Km. It is beautiful and promising: another great clue for intense detectives to follow.
