Assimilation and integration of Geodetic observations Into subduction earthquake Rupture modeling. – AGIR
Assimilation and integration of geodetic observations into subduction earthquake rupture modeling
The 2011 Mw9.0 Tohoku earthquake (Japan) shocked the worldwide seismologist community by demonstrating that we could not anticipate exceptionally large earthquakes properly. Today’s failure is mostly due to the rare occurrence of such events. However, the increasing number of interseismic observations opens new perspectives. The strategy we develop here aims to take advantage of interseismic geodetic measurements, which can be used to infer the mechanical loading process of the plate interface.
Does the plate coupling coefficient map deduced from inter-seismic geodetic measurement provide a reliable insight to predict the future rupture area and patterns?
Earthquake occurs at the end of a so-called seismic cycle. During a long inter-seismic time, the stress loading increases along the plate boundaries, before mega-subduction earthquake eventually happen. Today, thanks to permanent GPS stations installed on subduction margins, we can measure the surface deformation associated with the deep loading. This observation could be used to estimate in advance the distribution of the future earthquake stress drop, one important parameter controlling the rupture. From this estimate, we could be able to compute future rupture scenarios, and help to mitigate tsunami and strong-motion hazards. <br /><br />The first objective of this project is to apply this idea to a place where an earthquake occurred (the 2010 Mw8.8 Maule earthquake in Chile), allowing to compare the blind prevision with the actual rupture distribution. Deeper investigations will be conducted on understanding and quantifying the limits of the approach, working more in details on the way plate-coupling is modelled, refining the notion of barriers and how can we assess their characteristics. <br /><br />The second objective of the project is to apply the method to other places where it can be used to anticipate the future rupture scenarios: namely identified gaps close to rupture in Chile and Japan.<br /><br />Finally, the project will contribute to one of the great challenge of modern seismology: rupture dynamic inversion. In the framework of this project, we propose to modify the dynamic inversion algorithm introducing a realistic a priori stress drop distribution that will reduce the number of inverted parameters and increase the reliability of the solutions. <br />
work in progress
work in progress
work in progress
work in progress
Earthquake occurs at the end of the seismic cycle. During a long time, the plate tectonics increase the stress loading along the plate boundaries, where mega-subduction earthquake eventually happen. Today, thanks to permanent GPS stations installed on subduction margins, we can measure the deformation of the crust associated with the subduction interface loading. This observation can be used to estimate in advance a crucial parameter of the earthquake in preparation: the stress drop. Knowing in advance the distribution of one of the two important parameters controlling the rupture enhances greatly the predictability of the future earthquake. By carefully evaluating the other parameters (the friction parameters), it is possible to compute future rupture scenarios, which can help to mitigate tsunami and strong-motion hazards. This new technique has been recently developed for the Nankai subduction zone, in Japan. However, a real earthquake did not validate the prediction technique. This is the first objective of this project: we need to apply the same technique to a monitored subduction zone where an earthquake occurred, to serve as a blind test. We will then compare the prevision made using only interseismic studies with the actual rupture. The discrepancies will be studied in order to improve the anticipation quality. This closely related to segmentation issues. What is responsible for the apparent segmentation of subduction zones? Can segmentation change over several seismic cycles?
Since our goal is to be able to determine reliably what will be the maximum extent of the future rupture, we need to study very large earthquakes, which occurred in sufficiently instrumented regions before the earthquake. There are two equivalent places in the world where we can develop this project: Japan, with the 2011 Mw9.0 Tohoku earthquake, and Chile, with the 2010 Mw8.8 Maule earthquake. The method was initially developed for the Nankai trough, and we have started the study of Tohoku earthquake recently, but Chile seems a better target for this initial part of the project, since ENS team has been working on Chile for years now, and have a stronger expertise than for Japan needed to understand the limitations of the modelling. Of course, developments for Chile will have a strong impact in Japan, and are likely to be applied there too. The final task will be to elaborate scenarios for identified gaps close to rupture in Chile, and in Japan.
Around the promising hopes of this approach, there are limitations that we want to investigate deeply. A second objective of this project is to model more precisely the interseismic deformation, and the corresponding stress accumulation on the slab. So far, simplified crustal models, and purely elastic behaviour are used to constrain the slip-deficit distribution. The elastic hypothesis is certainly valid for crustal behaviour at the time of the earthquake, but is it still a good hypothesis when looking at the long time interseismic loading? A related task is to investigate the role of spatial heterogeneities of friction at small scale on both earthquake preparation phase and the rupture. What is the meaning of the so-called plate-coupling rate? Are there different kinds of barriers? Can we locate barriers as well as asperities? There are several points we want to investigate which could improve our fundamental understanding of the mechanical processes leading to megathrust rupture.
Finally, the project will contribute to one of the great challenge of modern seismology: rupture dynamic inversion. This technique is not well developed due to several limitations. We propose to improve the method. We will modify the dynamic inversion algorithm to take advantage of the interseismic information. Introducing a realistic a priori stress drop distribution will reduce the number of inverted parameters and increase the reliability of the solutions. Here again, both Tohoku and Maule earthquakes are good candidates.
Project coordination
Sébastien HOK (Laboratoire de Géologie)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
Partner
LG-ENS Laboratoire de Géologie
Help of the ANR 118,961 euros
Beginning and duration of the scientific project:
October 2012
- 36 Months
