A novel method to identify the faults prone to break in the coming century, hence posing the most immediate risk – CENTURISK

Most populated regions worldwide are dissected by numerous active faults. The question we address is: within such dense networks of faults, can we recognize those that are prone to break in a large earthquake during our lifetime that is over the next century? Those ‘ready-to-break’ faults are those posing the most immediate hence highest risk to populations. We suggest that, if we can characterize (age, location, magnitude) the large earthquakes that have broken a fault over the last 1000s of years, then we can construct the empirical occurrence frequency curve of those earthquakes. That empirical function should reveal whether the fault is presently in a paroxysmal phase of seismic activity (many large earthquakes occurring in a narrow, <100-200 yrs, time window) hence prone to break over the next century, or rather in a more quiescent phase. At present, there exists no technique that allows recovering the long past earthquake histories that we need to reconstruct the above functions. We thus develop a novel approach that we expect successful to recover the traces of the 10-20 past large events on some target faults. We suggest that the memory of past large earthquakes has to be searched in the first 10s meters of the ground, where it is preserved as buried offset morphological markers. We thus combine three complementary, non-invasive, up-to-date geophysical techniques (3D GPR, Electric Tomography, and High-Resolution Seismic Imaging) to investigate at high-resolution the first 10s meters of the ground, along a few target faults chosen as best candidates for success. Doing so, we expect detecting the traces of a large number of past earthquakes, while measuring the displacements produced by those earthquakes hence estimating their magnitude. Combined with the dating of the identified events, our work should allow constructing the empirical occurrence frequency functions that we seek, and help identifying the faults most prone to break during our lifetime.