2:15 PM - 2:30 PM
[SCG55-13] Normal faults formed in horizontal compressive stress field
Keywords:mesoscale fault, multiple inverse method, paleostress, Niitsu Hill, Niigata Prefecture
Fault slip that occurs within one stress field is not necessarily uniform. To perform stress inverse analysis on small faults, there is a risk of leading to incorrect conclusions depending on the exceptional faults.
Miocene to Pleistocene sedimentary and volcanic rocks are distributed in the Niitsu Hills, Niigata Prefecture. Fold and fault structures suggesting W-E~NW-SE compression are developed. Property description and stress inverse analysis for small faults were performed. The 80 sets of slip data were collected for the Upper Miocene to Pliocene Kanazu Formation. The faults are N or S dipping, a few to 10s cm in separation. Most do not involve fault gouges. In addition, small displacement dense faults, and large displacement parallel faults with fault gouges are identified. The 20 sets of slip data were obtained for the Pleistocene Yashiroda Formation. The faults are NE or SW dipping in the upper member.
Stress analyses were performed using the multiple inversion method (Tomita & Yamaji, 2001). From the Kanazu Formation, Clusters 1, 2, and 3 were identified. All σ1 are vertical (normal fault type), σ3 is horizontal (Cluster 1), NNW-SSE(Cluster 2), and NE-SW (Cluster 3). The Cluster 3 is predominant on small displacement faults, and Cluster 2 on other faults. From the large displacement faults, strike-slip and normal types of solutions are coexist.
W-E compressional strike-slip stress fields were estimated at depths of over 4,000 m, and positive flower structure was imaged (Imamura and Iwata, 2004). The normal faults on the ground surface are extensional phenomena related to the anticline development. Cluster 2 is thought to have been formed by bending-moment fault, and Cluster 3 by elongation in the orientation of the anticline axis. The results from large-displacement faults are close to the deep stress field, deep fault movement probably reached to shallow levels.
Miocene to Pleistocene sedimentary and volcanic rocks are distributed in the Niitsu Hills, Niigata Prefecture. Fold and fault structures suggesting W-E~NW-SE compression are developed. Property description and stress inverse analysis for small faults were performed. The 80 sets of slip data were collected for the Upper Miocene to Pliocene Kanazu Formation. The faults are N or S dipping, a few to 10s cm in separation. Most do not involve fault gouges. In addition, small displacement dense faults, and large displacement parallel faults with fault gouges are identified. The 20 sets of slip data were obtained for the Pleistocene Yashiroda Formation. The faults are NE or SW dipping in the upper member.
Stress analyses were performed using the multiple inversion method (Tomita & Yamaji, 2001). From the Kanazu Formation, Clusters 1, 2, and 3 were identified. All σ1 are vertical (normal fault type), σ3 is horizontal (Cluster 1), NNW-SSE(Cluster 2), and NE-SW (Cluster 3). The Cluster 3 is predominant on small displacement faults, and Cluster 2 on other faults. From the large displacement faults, strike-slip and normal types of solutions are coexist.
W-E compressional strike-slip stress fields were estimated at depths of over 4,000 m, and positive flower structure was imaged (Imamura and Iwata, 2004). The normal faults on the ground surface are extensional phenomena related to the anticline development. Cluster 2 is thought to have been formed by bending-moment fault, and Cluster 3 by elongation in the orientation of the anticline axis. The results from large-displacement faults are close to the deep stress field, deep fault movement probably reached to shallow levels.