イラン南部のバム断層において2003年12月26日バム地震によって生じた地表変位

During the December 26th, 2006 Bam earthquake, continuous ruptures with a consistent rightlateral strike-slip of a few centimeters occurred north of Bam. A 3km long strand of ruptures coincides exactly with the trace of the geologic Bam fault. These ruptures were possibly caused by the tectonic slip on the source fault of the 2006 earthquake. The Bam scarp south of the Zehedan highway might have grown during the earthquake. The extension of the area around the scarp indicated by the scarp-parallel fissures may represent the coseismic stretch of the surface. South of the Bam scarp, there was no systematic surface effect. The absence of significant tectonic offset at the surface is concordant with the intermediate magnitude of Mw 6.6 Only a small and deep portion of the Bam fault, or another adjacent blind fault plane was ruptured in 2006. The geologic evidence of the over 50km long Bam fault suggests a large, probably M 7.5 or larger, event in the future, however, there is no historic and geologic data to quantify the risks

High-resolution seismic reflection survey across the Western Boundary Fault Zone of the Nagano Basin, Central Japan: Data acquisition and processing

The Western Boundary Fault Zone of the Nagano Basin borders the eastern margin of Northern Fossa Magna, which has undergone strong horizontal shortening since Pliocene. The Western Boundary Fault Zone of the Nagano Basin is considered to be a back thrust that developed on the hanging wall side of the Itoigawa-Shizuoka Tectonic Line. To reveal the subsurface structure of the Western Boundary Fault Zone of the Nagano Basin, we carried out a high-resolution seismic reflection survey along the Saigawa River, southern Nagano City. The source used in this survey was a mini-vibrator (T-15000). Source and receiver spacing was 10 m. 180 channels of geophone arrays were used to record each shot. The seismic section obtained after careful data processing shows fairly flat Quaternary basin fillings in the eastern part of the seismic line. The Quaternary basin fillings are interpreted to be in west-dipping fault contact with west-dipping Neogene strata underlying the Saigawa Hills

High-resolution seismic reflection profiling across the surface rupture associated with the 2004 Mid-Niigata Prefecture earthquake, central Japan : data acquisition and processing

The 200.4 Mid-Niigata Prefecture earthquake (Mj 6.8) generated surface ruptures along the eastern rim of the Uonuma hills. To reveal the relationship between a seismogenic source fault and surface ruptures, shallow, high-resolution seismic reflection profiling was undertaken across the surface ruptures and the active faults. The seismic source was a mini-vibrator and seismic data were recorded by a digital telemetry system. The source and receiver interval was 10 m4 The seismic data were processed using conventional CMP seismic reflection methods. The resultant depth-converted seismic section portrays an emergent thrust beneath the surface rupture associated with the Mid-Niigata Prefecture earthquake

High-resolution seismic reflection profiling across the Shiraiwa fault, eastern margin of the Yokote basin fault zone, northeast Japan : data acquisition and processing

The eastern margin of the Yokote basin fault zone extends about 56km at the western foot of the Ou Backbone Range, northeast Japan. The Rikuu earthquake (M=7.2) occurred in the Ou Backbone Range (Mahiru Range) on 31st August, 1896. Associated with this earthquake, four thrust faults-Obonai, Shiraiwa, Ota, and Senya fault3 appeared on the surface of the western foot of the Mahiru Range. These faults were highly sinuous with numerous gaps and en echelon steps. We conducted a high-resolution seismic reflection profiling survey across the Shiraiwa fault. The obtained seismic reflection data were processed by conventional common mid-point methods, post-stack migration, and depth conversion. The subsurface structure across the Shraiwa fault is characterized by branched low-angle reverse faults and conjugate back-thrust. The emergent thrust associated with the 1896 earthquake is regarded to be a subsidiary reverse fault

Surface effects of the December 26th,2003 Bam earthquake along the Bam fault in southeastern Iran

During the December 26th, 2006 Bam earthquake, continuous ruptures with a consistent rightlateral strike-slip of a few centimeters occurred north of Bam. A 3km long strand of ruptures coincides exactly with the trace of the geologic Bam fault. These ruptures were possibly caused by the tectonic slip on the source fault of the 2006 earthquake. The Bam scarp south of the Zehedan highway might have grown during the earthquake. The extension of the area around the scarp indicated by the scarp-parallel fissures may represent the coseismic stretch of the surface. South of the Bam scarp, there was no systematic surface effect. The absence of significant tectonic offset at the surface is concordant with the intermediate magnitude of Mw 6.6 Only a small and deep portion of the Bam fault, or another adjacent blind fault plane was ruptured in 2006. The geologic evidence of the over 50km long Bam fault suggests a large, probably M 7.5 or larger, event in the future, however, there is no historic and geologic data to quantify the risks

Shallow seismic reflection profiling across the central part of the Tokachi active fault zone, Hokkaido, Japan

The Tokachi active fault zone, a chain of active faults and flextures 80 km long from north to south, exists as the topographic boundary between the Tokachi Plain and the eastern uplands, Hokkaido, Japan. We carried out shallow seismic reflection profiling using a mini-vibrator to clarify the implications between surface deformation and subsurface structures of this fault zone at the most highly active area of the Makubetsu Plateau. The results obtained are as follows. Two distinct flexures are recognized in the seismic reflection profile. The western flexure is about 2 km wide and has at least a 0.25 to 0.30 second vertical displacement, whose sense is concordant with the deformation of the surface of the upper fluvial terraces geomorphologically identified as the Tobatsugawa fault. The eastern one also has the same deformation pattern of fluvial terraces as that geomorphologically identified as the Itaira fault. However, both geomorphic flexures are below one-sixth to one-third of the subsurface flexural zone in width. The seismic reflection method is necessarily required, to evaluate the net displacement of active flexural zone, in addition to morphotectonic observations

High-Resolution P-wave Seismic Reflection Imaging of the Suzuka Basement-Involved Fold : 2005 Tokiyama Profile

We present new, high-resolution seismic reflection data (2005 Tokiyama profile) acquired across the piggyback basin between the Yoro and Suzuka basement-involved folds to further image its subsurface geometry. A seismic source (mini-vibrator) and 180-channel digital telemetry recording system were used in an split-spread configuration with the nearest receiver adjacent to the source to record seismic waves from deeper reflection points. A 10-m source and geophone spacing give a 5-m CMP (common midpoint) spacing on the final section. The nominal CMP stacking fold had 90 traces. We also suppressed coherent noise by repeating source points 7-10 times. After data processing including surface-consistent statics, velocity analysis, normal moveout (NMO) correction, residual statics, CMP stack, and migration, the section was finally depth-converted using stacking velocities. Reflectors imaged on the seismic profile Illuminate that the forelimb composed of Pliocene-Pleistocene Tokai Group and underlying Mesozoic basement rocks are thrust over intermontane units. The uniform thickness of the Tokai Group on the west flank of the Yoro Mountains also indicates its pregrowth nature to the Yoro basement-involved fold

High-Resolution P-wave Seismic Reflection Imaging of the Suzuka Basement-Involved Fold : 2005 Nishi-Nojiri Profile

We present new, high-resolution seismic reflection data (2005 Nishi-Nojiri profile) acquired across the forelimb of the Suzuka basement-involved fold and Ichinohara flexure to further image their subsurface geometries. A seismic source (mini-vibrator) and 180-channel digital telemetry recording system were used in an off-end configuration with the nearest receiver adjacent to the source to record seismic waves from deeper reflection points. A 10-m source and geophone spacing give a 5-m CMP (common midpoint) spacing on the final section. The nominal CMP stacking fold had 90 traces. We also suppressed coherent noise by repeating source points 5 times. After data processing including surface-consistent statics, velocity analysis, normal moveout (NMO) correction, residual statics, CMP stack, and migration, the section was finally depth-converted using stacking velocities. Reflectors imaged on the seismic profile Illuminate that the forelimb composed of Pliocene-Pleistocene Tokai Group and underlying Mesozoic basement rocks are thrust over the Tokai Group in the footwall