The abundance of seismological, geodetic, morphotectonic and structural data for Central Japan allows an integrated approach to the study of recent tectonics. This study has been conducted in a region where an apparent uniformity of geodynamic conditions existed during Quaternary times. Four independent data sets have been collected: minor and major earthquakes, mesoscale faults, and large scale morphological dislocations. All of them have been reduced to a common format including fault plane orientation, direction and sense of movement. The analysis has been carried out by applying different methodologies commonly employed in structural geology in order to obtain both qualitative and quantitative estimates of the stress field, where the latter kind of analyses also provides the principal stress directions and the ratio R = (sigma1-sigma2)/(sigma1-sigma3). The results of each data set are internally consistent. But above all, the similarity between the three principal stress directions of the four data sets is straightforward, showing a clear strike-slip regime with an ESE-WNW trending sigma1 and a NNE-SSW trending sigma3 whose averages are 288°/05° and 198°/10° respectively. Numerous geodetic data from the region show exactly the same direction of minimum horizontal strain (i.e. maximum contraction) and broadly confirm previous large scale stress trajectories maps. By considering characteristic depth, age, fault dimension etc. for each fault set, it is possible to understand better the recent (Late Quaternary-Present) tectonic evolution of the area where a progressive NNE-SSW restraining appears to occur. Due to the possible westward migration of the compressional zone associated with the Itoigawa-Shizuoka Tectonic Line, or the southern increasing constrain produced by the Philippine Sea Plate, this geodynamic process will eventually produce a permanent swap of the sigma2 and sigma3 axes.
An integrated study to recent tectonics in Central Japan: seismological, geodetic, morphotectonic and structural data compared
CAPUTO, Riccardo;
1996
Abstract
The abundance of seismological, geodetic, morphotectonic and structural data for Central Japan allows an integrated approach to the study of recent tectonics. This study has been conducted in a region where an apparent uniformity of geodynamic conditions existed during Quaternary times. Four independent data sets have been collected: minor and major earthquakes, mesoscale faults, and large scale morphological dislocations. All of them have been reduced to a common format including fault plane orientation, direction and sense of movement. The analysis has been carried out by applying different methodologies commonly employed in structural geology in order to obtain both qualitative and quantitative estimates of the stress field, where the latter kind of analyses also provides the principal stress directions and the ratio R = (sigma1-sigma2)/(sigma1-sigma3). The results of each data set are internally consistent. But above all, the similarity between the three principal stress directions of the four data sets is straightforward, showing a clear strike-slip regime with an ESE-WNW trending sigma1 and a NNE-SSW trending sigma3 whose averages are 288°/05° and 198°/10° respectively. Numerous geodetic data from the region show exactly the same direction of minimum horizontal strain (i.e. maximum contraction) and broadly confirm previous large scale stress trajectories maps. By considering characteristic depth, age, fault dimension etc. for each fault set, it is possible to understand better the recent (Late Quaternary-Present) tectonic evolution of the area where a progressive NNE-SSW restraining appears to occur. Due to the possible westward migration of the compressional zone associated with the Itoigawa-Shizuoka Tectonic Line, or the southern increasing constrain produced by the Philippine Sea Plate, this geodynamic process will eventually produce a permanent swap of the sigma2 and sigma3 axes.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
