TU Scientists Participate in New Earthquake Study

The 2016 Mw 7.6 earthquake of Southern Chile was the first large earthquake to occur within the rupture bounds of the great 1960 Mw 9.5 Valdivia earthquake, the largest ever observed in historical times.

Using GPS, InSAR, gravity, seismic reflection, and geological data, an international team led by GermanResearchCenter for Geoscience GFZ in Potsdam and joined by TU Dresden scientist Dr. Benjamin Gutknecht, show that the 2016 earthquake occurred at the deep boundary of a persistent asperity on the interface between the subducting Nazca and overriding South American plates. Here, both plates are coupled and not sliding past each other in spite of the high convergence velocity of 68 mm/year. This asperity broke during the 1960 Chile earthquake and had since healed and recovered.

Their study, published in Nature Geoscience, presents a mechanical model in which the highest stresses gradually accumulate at the deeper edge of an asperity. Depending on the frictional parameters of the asperity and the deeper segment of the plate interface, the model predicts the failure times of the interface.

Given the lag time of 56 years since the 1960 event, the model suggests that the pressure of fluid at the plate interface zone is close to lithostatic at the deeper interface. If the water pressure at the plate interface zone becomes as high as the pressure of the overlying rock column, the strength of the rocks at the plate interface becomes practically zero and an earthquake will eventually be triggered.

It is proposed that the development of this modelling strategy could enable the estimation of critical failure thresholds for other mapped subduction asperities where subducting and overriding plates are currently locked.
 

Original study: Moreno, M., Li, S., Melnick, D., Bedford, J. R., Baez, J. C., Motagh, M., Metzger, S., Vajedian, S., Sippl, C., Gutknecht, B. D., Contreras-Reyes, E., Deng, Z., Tassara, A., Oncken, O., 2018. Chilean megathrust earthquake recurrence linked to frictional contrast at depth. Nature Geoscience. DOI: 10.1038/s41561-018-0089-5

GFZ Potsdam press release: https://www.gfz-potsdam.de/en/media-and-communication/news/details/article/aquaplaning-in-the-geological-underground/