Although recent GPS observations have made it possible to detect crustal strain precisely and extensively,we have not yet observed a whole cycle of strain buildup and release in orogenic zones by any geodetic methods....Although recent GPS observations have made it possible to detect crustal strain precisely and extensively,we have not yet observed a whole cycle of strain buildup and release in orogenic zones by any geodetic methods.From the viewpoint of earthquake forecasting,we need to extract elastic strain from GPS-derived strain data.However,we do not have any(practical)geophysical method by which to discriminate between elastic and inelastic strains from GPS data.Based on the lesson from the 2011 Tohoku earthquake of Mw 9.0,we propose here that geological methods(and ways of thinking as well)should be used to estimate inelastic strain buildup quantitatively,thereby to evaluate present-day elastic strain buildup,which may eventually cause gigantic earthquakes.We review here a case history of the 2011 Tohoku earthquake,and present a global comparison with other gigantic(Mw≥9.0)subduction earthquakes in the world.展开更多
Gravimetric and geologic data show that the reactivation of the Neogene Interandean depression and/or the ~75 - 65 Ma ophiolite suture into the modern dynamic of the Andes controlled the Gulf of Guayaquil Tumbes basin...Gravimetric and geologic data show that the reactivation of the Neogene Interandean depression and/or the ~75 - 65 Ma ophiolite suture into the modern dynamic of the Andes controlled the Gulf of Guayaquil Tumbes basin (GGTB) location and evolution during the past 1.8 - 1.6 Myr at least. Depending on whether the remobilization occurred along the interandean depression or the ophiolite suture, the GGTB evolved trough pure or simple shear mechanisms, respectively. Because the GGTB exhibits an along strike tectonic asymmetry associated with a pervasive seismic gap, the simple shear solution is more likely. Tectonic inversion occurred along a mid-crust detachment (the Mid-Crust detachment hereafter) matching the ophiolite suture that accommodates the North Andean Block (NAB) northward drift. The so-called Decoupling Strip located at the shelf slope break accommodated the tensional stress rotation from N-S along the shelf area i.e. NAB-drift induced to E-W along the continental margin i.e. subduction-erosion-induced. The landward dipping Woollard detachment system located at the Upper-Lower slope boundary connects the subduction channel at depth, allowing the Upper slope to evolve independently from the Lower slope wedge. The long-term recurrence interval between earthquakes, the strong interplate coupling, and the aseismic creeping deformation acting along the main low-angle detachments i.e. the Woollard and the Mid-Crust detachments may account for the pervasive seismic gap at the GGTB area. Because the subduction channel exhibits no record of significant seismic activity, no evidence exists to establish a link between the GGTB sustained subsidence and a basin-centered asperity. Because the GGTB is a promising site of hydrocarbon resources, to understand processes at the origin of this escape-induced forearc basin has a major economic interest.展开更多
文摘Although recent GPS observations have made it possible to detect crustal strain precisely and extensively,we have not yet observed a whole cycle of strain buildup and release in orogenic zones by any geodetic methods.From the viewpoint of earthquake forecasting,we need to extract elastic strain from GPS-derived strain data.However,we do not have any(practical)geophysical method by which to discriminate between elastic and inelastic strains from GPS data.Based on the lesson from the 2011 Tohoku earthquake of Mw 9.0,we propose here that geological methods(and ways of thinking as well)should be used to estimate inelastic strain buildup quantitatively,thereby to evaluate present-day elastic strain buildup,which may eventually cause gigantic earthquakes.We review here a case history of the 2011 Tohoku earthquake,and present a global comparison with other gigantic(Mw≥9.0)subduction earthquakes in the world.
文摘Gravimetric and geologic data show that the reactivation of the Neogene Interandean depression and/or the ~75 - 65 Ma ophiolite suture into the modern dynamic of the Andes controlled the Gulf of Guayaquil Tumbes basin (GGTB) location and evolution during the past 1.8 - 1.6 Myr at least. Depending on whether the remobilization occurred along the interandean depression or the ophiolite suture, the GGTB evolved trough pure or simple shear mechanisms, respectively. Because the GGTB exhibits an along strike tectonic asymmetry associated with a pervasive seismic gap, the simple shear solution is more likely. Tectonic inversion occurred along a mid-crust detachment (the Mid-Crust detachment hereafter) matching the ophiolite suture that accommodates the North Andean Block (NAB) northward drift. The so-called Decoupling Strip located at the shelf slope break accommodated the tensional stress rotation from N-S along the shelf area i.e. NAB-drift induced to E-W along the continental margin i.e. subduction-erosion-induced. The landward dipping Woollard detachment system located at the Upper-Lower slope boundary connects the subduction channel at depth, allowing the Upper slope to evolve independently from the Lower slope wedge. The long-term recurrence interval between earthquakes, the strong interplate coupling, and the aseismic creeping deformation acting along the main low-angle detachments i.e. the Woollard and the Mid-Crust detachments may account for the pervasive seismic gap at the GGTB area. Because the subduction channel exhibits no record of significant seismic activity, no evidence exists to establish a link between the GGTB sustained subsidence and a basin-centered asperity. Because the GGTB is a promising site of hydrocarbon resources, to understand processes at the origin of this escape-induced forearc basin has a major economic interest.
