Drilling into Seismogenic Zone And Exploration Geophysics

摘要

Geological observation have been carried out on faults which appeared on the earth's surface after earthquakes, although fault failures were initiated and propagated in the deep underground. Similarly, seismic studies were based on simplified fault plane models, although seismic ruptures had radiated seismic waves at depths deeper than a few kilometers along faults of unknown plane surface properties. These days, various seismic inversion studies indicate that fault planes are not uniform so that seismic signals generated at a fault plane are functions of space and time. These facts clearly imply that studies need to he made in depths for investigating parameters differing the generated earthquake signals at the fault plane from a simple fault rupturing process. There is, indeed, a necessity to conduct a joint study on earthquake faults in terms of their kinematics from multidisciplinary point of view for further studying earthquakes in geological settings of fault planes and eventually in their generation mechanisms. Drilling would provide a clue to correlate physical properties of rocks surrounding earthquake faults with earthquake generation/propagation mechanisms. After reviewing what would be necessary to understand fault behavior in seismology, we concluded the following: (1) Understanding fluid flow around fault planes is of importance as in exploration geophysics, (2) Property mapping is an indispensable method even for seismological studies, (3) Logging tools must be optimized in their calibration or in response function for rocks in seismogenic zones, (4) Parameters for scaling and constitutive laws need to be considered as an application of the future exploration target, and (5) long-term monitoring is strongly needed to monitor possible changes in physical properties in an earthquake generation cycle.