Subduction zones with potential for PSInSAR investigation for space-based reduction

The use of PSInSAR (Permanent Scatterer Interferometric Synthetic Aperture Radar) for the study of tectonic deformation has been studied in the context of earthquake risk reduction in the course of the project PSIGN (Musson and Bommer 2002, Musson et al 2002, 2003, 2004 and PSIGN project reports). The test area used in this study was the Tokai area of Honshu, Japan, as this is an area where a devastating great earthquake is considered to be imminent. The study showed that preseismic deformation associated with this impending earthquake could be detected, and these space-based results are confirmed by other methods, including GPS but more importantly, ground levelling studies. The PSIGN study area is characterised tectonically by a process known as subduction, where one crustal plate (usually oceanic) is being pushed under an over-riding plate (usually continental), down into the earth's mantle, to be destroyed at depth. Because of the broad, shallow-dipping interface between the two plates in such a situation, fault ruptures can have a large area and therefore produce much bigger earthquakes than is possible in other tectonic regimes (such as California). Earthquake risk in such areas is therefore a matter of great concern. Previous studies in Japan, e.g. those by Yoshioka et al (1993) and Sagiya (1999) have shown that deformation data of this kind can be used to image the locked part of a subducting plate using a mathematical process referred to as the ABIC method (Akaike's Bayesian Information Criterion). Although the PSIGN data has not yet been used in this way (it could be, and we hope that it will be in a future study), as it provides very dense data coverage it has the potential to give a better resolution of the locked zone than could be achieved with other types of data. In the case of Japan, it has been possible to use the ABIC method in the past because of the existence of good levelling and GPS data. In other parts of the world where such data do not exist in sufficient degree (or do not exist at all), the availability of PSInSAR as a resource would be particularly valuable. This report provides a short survey of the major subduction zones of the world where PSInSAR could conceivably be used. It considers in particular the tectonic configuration, past seismicity, and the human vulnerability of these zones. Issues relating to the availability of suitable lnSAR data archives are not addressed.