Precaution fault zones designated by Matsuda (1981) are reevaluated using recently-obtained data on the late Quaternary slip-rate and from the result of excavation studies for faults of historical earthquakes. The precaution faults were defined as those with elapse ratio, E=t/R>0.5 (t: elapsed years since the last activity. R: average recurrence interval). The following three fault z o nes can be excluded from the previously-denoted precaution zones: The Arima-Takatsuki tectonic line (t/R=0.1∼0.4), which have moved in 1596. The Rokko-Awaji fault zone (t/R=0.0∼0.5), of which southern part moved in 1995 and northern part probably in 1586. The Atera fault zone (t/R= 0.3∼0.5 for M8.0 ), which have moved in 1586. The following fault zones are ascertained to be precaution faults. Segments of the Median Tectonic Line of central Shikoku to central Kii (t/R=0.5∼2.5 for M7.8). The Inadani fault zone (t/R>0.6∼1.6). The central part of Itoigawa-Shizuoka tectonic line (t/R=0.9), which moved about 1200 years ago. The Fujikawa fault zone (t/R>0.9∼1.4). The Kozu. Matsuda-Kannawa fault zone (t/R>1.0∼2.8).
On the basis of fossil liquefaction structures observed in the Hokkaido University campus, paleoearthquakes that had struck Sapporo-city are discussed. The results are as follows: (1)Paleoearthquakes had occurred three times during last ca. two thousand and several hundred years. The latest paleoearthquake should be identified with the 1834 Ishikari-earthquake. The older paleoearthquakes occurred at around 2000 years BP. and during the time between A. D.10. century and the end of A. D.18. century, respectively. (2) The return period of earthquake is estimated to be from 2000 to several hundred years. (3) Active fault which caused liquefaction can not be decided, because of lack of the historical records.
The evidence of eastward thrusting of the Neogene system onto Quaternary sedimentary fill is shown in the western marginal area of the Kitakami Lowland, west of Hanamaki City. The dip and strike of the fault surface are N44-46°E and 67-78°N, respectively. The fault surface is inclined at an higher angle than those develop in the Quaternary system to the east, which indicates that they converge upon each other beneath the ground surface.
Trench excavation across the surface rupture of the 1995 Hyogoken-nambu Earthquake revealed at least two and possibly three surface-faulting events including the 1995 earthquake on the Nojima Fault during the past 2000 years. A pre-1995 event probably occurred about 400 years ago and this event may be correlated to the Keicho Earthquake of 1596. An event before the pre-1995 event occurred about 2000 years ago.
In this paper, we investigated the various fault features of the Iyo fault and depicted fault lines on detailed topographic map. The results of this paper are summarized as follows; 1) Distinct evidence of the right-lateral movement is continuously discernible along the Iyo fault.2) Active fault traces are remarkably linear suggesting that the angle of fault plane is high.3) The Iyo fault can be divided into four segments by jogs between left-stepping traces.4) The mean slip rate is 1.3∼1.6 mm/yr. laterally, and is 0.17∼0.2 m m/yr. vertically.5) Offset stream ratio a: D/L, where D is horizontal displacement and L is length of th e river upstream from the fault, is 0.55∼0.09 for the Iyo fault. Based on the offset stream ratio, the mean slip rate of the Iyo fault is roughly estimated 1∼5 mm/yr. and the fault is classified as class A in activity.
Some outcrops of the Otake fault in the Iwakuni Active fault System, where the Otake fault cuts Quaternary gravel beds, were first found. The gravel beds are presumably estimated as late Pleistocene sediments from their facies and relative heights. According to the direction of striations on the fault plane, the latest movement of the Otake fault may have been right lateral slip having the component of a reverse fault. On the other hand, micro earthquakes recently occur around the north of the Otake fault and their focal mechanisms show nodal planes of NE-SW and NNW-SSE directions. The nodal planes of NE-SW direction correspond to the plane of the Otake fault. Although this does not immediately imply that the Otake fault is now active, further observations are necessary.
An active fault, named Kokura-Higashi fault, runs from the eastern and the southern parts of Kokura city with clear fault topography. The fault is considered to cause great earthquakes in the vicinity of the city. By the observation of the aerial photographs and by the investigation on the subsurface geology, the followings become clear. 1. Fluvial terr aces exist along this fault. The gravels which constitute these terraces are very reddish and deeply weathered. Thus, the author renamed them as the old terraces. Terraces lower than those are renamed as new terraces in this paper. 2. The age of the old terrace is at least older than 130 thousands years. 3. Almost all the old terraces are covered with the Aso-4 tephras. 4. The old terraces are all displaced by this fault. In Oba t ake, the gravel constituting the old terrace come in contact by fault with clay which lies under the gravel. The new terrace distributing at the southern extremity is not displaced by the fault. 5. The displacements of the old terrace is 3-11m, and the western side of the fault is uplifted. The amount of displacements increase to the south along the fault and decreases at the southern end. 6. The average slip-rate of the fault is 0.023-0.085m/1000y.
This paper describes some fault outcrops and internal structures of fault rocks along the Fl fault in the Tan-Lu Fracture-zone in Linyi area, Shandong Province, China. The Fl fault zone is composed of two-type fault rocks; one is cataclasites showing complex fold structures and the other is incoherent, foliated fault breccias and gouges. The former is larger than a few tens of meters in thickness, whereas the later is generally less than a few meters in thickness. Foliations and R1 Riedel shear surfaces observed at outcrops are characterized by the alignment of clasts and the development of subsidary shear surfaces. Most clasts included in fault breccias and gouges are rounded or sub-rounded in shape and aligned sub-parallel to the main shear plane (F1 fault plane). They generally show an asymmetry in shape. The internal structures of incoherent fault rocks and tectonic topogr a phies show that the Fl fault was reactivated in the Late Quaternary as a high-angle reverse or normal fault with some right-lateral strike-slip component, which is different from the previous faulting along the Tan-Lu Fracture-zone before the Quaternary. The relation between the tectonic topographies and the fractured zone suggests that the incoherent cataclastic rocks formed in the Late Quaternary mainly by a high-angle reverse or normal faulting along the old Tan-Lu Fracture-zone.
The surface ruptures appeared on the ends of main trace of the Nojima Earthquake Fault which occurred on the northwestern side of Awaji Island accompanying the 1995 Southern Hyogo Prefecture Earthquake in Japan. The northern end part of the earthquake fault is composed of two surface rupture zones of striking N50°-80°W and branching obliquely from the main trace of the earthquake fault. The southern end part of the earthquake fault consists of discontinuous surface ruptures, progressive flexures and some slope failures, which are concentrated in a narrow zone at most a few tens of meters wide and several kilometers long. The displacements along these surface ruptures are generally less than 20cm both in horizontal and vertical, and don't depend on geologic and geomorphologic boundary. The geodetic data show that there were some coseismic displacements both in horizontal and vertical along the surface ruptures in the southern part of the earthquake fault. The aftershock distributions in January 17,1995 show a tendency to be concentrated on the area around the southern end (Ichinomiya Town) of the earthquake fault. The harmonious characteristics of the deformational topographies, geodetic and aftershock distributions suggest that the surface ruptures were formed on the ends of main trace of the Nojima Earthquake Fault by tectonic movement accompanying the earthquake.