Active Strike-slip Fault Research Articles

PREHISTORIC LARGE EARTHQUAKES DEDUCED FROM FAULT ACTIVITIES ALONG THE ATERA FAULT, CENTRAL JAPAN

Prehistoric fault activities along the Atera fault, one of the most prominent active strike slip faults in central Japan, have been revealed from studies on faulted humic soil layers and river terraces. Many organic samples for radiocarbon datings were collected from the outcrop on the Atera fault at Rgo, Kashimo Village, Gifu Prefecture, in order to determine the periods of prehistoric earthquakes. Displacements of river terraces around Sakashita Town on the right bank of the Kiso river, have been measured in order to deduce the amounts of coseisimic displacements. Prehistoric earthquakes deduced from fault activities have been repeatedly taken place along the fault at the periods of before 10, 300 y. B. P., 7, 900 y. B. P., 5, 500 y. B. P, and 1, 850 y. B. P., Recurrence intervals between succeeding two earthquakes are not equal but differ from each other judging from the amounts of displacements associated with each earthquake. The average vertical slip rate has been calculated as 0.71 m/103 yrs. from the amounts of coseismic displacements obtained from faulted river terraces and the receurrence intervals of earthquakes. The average lateral slip rate is calculated as 3.55 m/103 yrs., since it is known that the left lateral displacement is about 5 times larger than the vertical one (Sugimura and Matsuda, 1965). Along the Atera fault a great earthquake is presumed to occur within a thousand years in future, based on “Time-predictable recurrence model for large earthquakes” (Shimazaki and Nakata 1980).

Mesozoic Accretionary Tectonics of Alaska: ABSTRACT

Most of Alaska represents an enormous mosaic of allochthonous tectono-stratigraphic terranes, each characterized by a distinctive pre-Tertiary stratigraphic and tectonic history. More than 40 terranes presently are recognized, ranging in size from thousands of square kilometers to unique tectonic blocks having outcrop areas of only a few square kilometers. With a single exception, all of these pre-Tertiary terranes evidently are allochthonous with respect to North America and to one another. Some are best interpreted as displaced parts of the continental margin, but others--particularly in southern Alaska--may be exotic to North America. Paleomagnetic studies show that some terranes such as Wrangellia, have been transported as much as 3,000 km. Amalgamation of different terranes prior to final emplacement can be documented or inferred in a few places, but most of Alaska was tectonically assembled from individual lithosphere fragments and microplates during late Mesozoic time by complex accretion. Various schemes have been proposed for rotation and/or offset of northern Alaska into its present position. In south-central Alaska, southwest-trending terranes generally parallel the present-day Aleutian trench system. Outcrop patterns of rocks within these terranes point to mainly convergent late Mesozoic accretionary tectonics involving the development of nappes. Subsequent strike-slip faulting of these terranes is relatively minor, but original Mesozoic accretion of these belts may have involved large-scale transform displacemen along the northwest-trending parts of the Tintina trench and ancestral Denali fault systems. Significant tectonic displacement continues only along the active strike-slip faults in southeast Alaska and accretion is limited to the mechanically related Aleutian trench system. End_of_Article - Last_Page 784------------

A deep-sea hydrothermal site on a strike-slip fault

Submersible exploration of a young scarp in the San Clemente fault zone, at 1,800 m in the California Borderland, discovered tall piles of hydrothermal barite and dense colonies of large benthic animals. Phenomena along this active strike-slip fault zone resemble those at hot springs along the axes of mid-ocean ridges.

The North Anatolian transform fault: its age, offset and tectonic significance

The North Anatolian transform fault is a morphologically distinct and seismically active strike-slip fault which extends for about 1200 km from Karliova to the Gulf of Saros along the Black Sea mountains of N. Anatolia. It takes up the relative motion between the Black Sea and the Anatolian plates, thereby connecting the E. Anatolian convergent zone with the Hellenic Trench through the complex plate boundary zone of the Aegean. For most of its length, the transform has a typical strike-slip fault zone morphology, characterized by narrow ‘rift zone,’ offset, captured and dammed streams, sag ponds and other deformed morphological features. The fault zone is a broad region of extensively crushed country rock cut by a number of parallel and/or anastomosing strike-slip faults. The transform has periods of seismic activity the last of which, from 1939 to the present, is characterized by frequent 6 ≤ M≤7earthquakes; these are separated by quiet periods of about 150 years. The crust along the fault zone is thinner than normal. The transform probably originated some time between the Burdigalian and the Pliocene and has an offset of about 85 km. Whether the offset of the fault changes systematically along its strike is not known. The North Anatolian transform fault seems to have originated as a consequence of the Arabia-Anatolia collision durmg the late (?middle) Miocene, when the Anatolian Plate originated and was wedged out into the oceanic tract of the E. Mediterranean from the converging jaws of Arabia and Eurasia to prevent excessive crustal thickening in E. Anatolia. The westerly motion of Anatolia with respect to Eurasia and Africa caused a great change in the tectonic evolution of the eastern Mediterranean, giving rise to the Aegean extensional regime and to internal deformation of Anatolia.

On stress accumulation and fault slip in the lithosphere

A mechanism of accumulation of shear stress in the neighborhood of a locked vertical strike-slip fault in the lithosphere is considered. The fault is taken to be situated in an elastic layer resting on and in welded contact with, a visco-elastic half space, in which shear stresses are maintained far away from the fault by tectonic forces. Exact solutions are obtained for the displacements and stresses in the system in the absence of fault slip, taking into account the displacements and stresses present initia1ly. It is shown that stress accumulation would occur continuously in the upper layer near the fault ti1l the fault slips suddenly, generating an earthquake. Exact solutions are next obtained for the displacements and stresses fo1lowing the fault slip, taking into account the displacements and stresses present before fault slip, and it is shown that stress accumulation would again occur in the upper layer, ti1l the fault slips again. The mathematical results are applied to some relevant observations on the accumulation of shear strain in the neighborhood of the San Adreas fault. It is shown that comparison of the mathematical results obtained and the observations on the ground deformations on the surface near the fault can be used to arrive at reasonable estimates for the times between consecutive slips on the active strike slip faults. The results are also expected to lead to greater insight into the problem of earthquake prediction. It is shown that, if sufficient data on surface deformation are available, the results can be used to estimate the effective viscosity of the lower lithosphere.

Near-Bottom Reconnaissance of a Fast-Slipping Transform Fault Zone at the Pacific-Nazca Plate Boundary

A 9 km length of the fast-slipping (152 mm/yr) Quebrada transform fault zone near 4°S on the East Pacific Rise was examined with deeply towed sonars and cameras. The fault zone occupies a 7 km-wide transform valley, which is a graben with step-faulted walls thickly mantled by pillow-basalt talus. Left-lateral strike-slip faulting is concentrated in a single narrow (< 200 m-wide) crush belt near the foot of the younger wall. The fault outcrops within a 20-50 m deep furrow that parallels the direction of plate separation and is similar to the topographic rifts'* along some continental strike-slip faults. The older, deeper, part of the valley floor, south of the active strike-slip fault, has been broken into secondary horsts and grabens by tensional faults that are 45° oblique to the strike-slip trend. The valley floor has experienced differential sediment deposition from an eastward bottom current, and part of the deepest graben has been flooded with young pahoehoe flows. There is increased volcanism in fa...

Late Quaternary tectonic movements of western and central Asia

Late Pleistocene and Holocene activity on major faults of western and central Asia are inferred from offsets of young topography. Large active strike-slip faults bound the northward-moving Arabian and Indian plates. The Indian plate moves more rapidly with respect to Eurasia than does the Arabian plate, with the highest rate of young lateral motion (1.2 to 1.4 cm/yr) along the Darvaz fault on its northwestern side. Convergence of these plates on the Eurasian plate produces the north-trending compression of the latter. It results in the creation of northwest-trending dextral wrench faults, smaller northeast-trending sinistral faults, east-west–trending thrust faults, and rare north-trending normal and extension faults. The rates of relative motion are slower here than on the borders of the southern plates, being higher to the north of the Indian plate than to the north of the Arabian. Not all relative motion of the southern plates is accommodated by their boundary deformation and by the compression of the Eurasian plate. This motion and resistance of the Eurasian plate produce squeezing of the rock masses on both sides of the southern plates that results in dextral west-trending wrench faulting on the western side and sinistral on the eastern side of each plate. This pattern can be recognized throughout the Neogene-Quaternary tectonic evolution of the Asian segment of the Alpine–central Asian orogenic belt. This paper is an attempt to correlate synchronous tectonic movements over huge areas of the continent. The author believes it is appropriate to recognize in such correlation mobile and stable zones of different scales. The depth and character of motion in the mobile zones define important features of the structure and evolution of the Earth9s crust.

Computer simulation of earthquakes

In a computer simulation study of earthquakes a seismically active strike slip fault is represented by coupled mechanical blocks which are driven by a moving plate and which slide on a friction surface. Elastic forces and time independent friction are used to generate main shock events, while viscoelastic forces and time dependent friction add aftershock features. The study reveals that the size, length, and time and place of event occurrence are strongly influenced by the magnitude and degree of homogeneity in the elastic, viscous, and friction parameters of the fault region. For example, periodically reoccurring similar events are observed in simulations with near-homogeneous parameters along the fault, whereas seismic gaps are a common feature of simulations employing large variations in the fault parameters. The study also reveals correlations between strain energy release and fault length and average displacement and between main shock and aftershock displacements.

Studies of Active Faults in Japan

The term “active fault (Katsu-danso)” appeared in the 1920's in papers of some geomorphologists in Japan. It has been used for faults active in Quaternary or late Quaternary, although the usage of the word “active” and its age-limit are different by authors. At any rate, the active fault is significant in geology in that the evidence of fault movements is recorded in the topography on the fault trace which enables detail analysis of the faulting, and in that the faulting might be detectable by means of geophysical methods, and it might be closely related to the occurrence of an earthquake. Recent studies in Japan showed that an active fault moves under a regionally-stressed condition of the crust, which has persisted during recent geologic time. If so, an “active fault” could be defined as a fault which is active under the present-day stress system. Then, the origin, orientation, and variation in time and space, of the “present” stress system are to be an important and fruitful research subject on the Tertiary to Quaternary tectonic history of the Japanese Islands. Some of the recent investigation on the active fault began to focus on this line.Studies of active faults in Japan have started from two points: the geological studies of the earthquake faults by geologists and the studies of the fault topography by geomorphologists.The geological studies of the earthquake fault was commenced by Koto, B. (1894) who had observed the surface break of the Mino-Owari earthquake of 1891 along the Neo Valley fault. Since then, geologists have investigated and described more than ten earthquake faults from Japan and Formosa. Particularly through the experiences of 1927- and 1930-earthquakes, it became clear that the mode of displacement along the earthquake fault during the earthquake is the same in the sense of displacement as the mode of the long-term displacement through the geologic periods. For example, Kuno, H. (1936) found that the Tanna fault which moved a few meters left-laterally during 1930 earthquake, has accumulated left-lateral displacement ca. 1000m since the middle Pleistocene.Almost independently of the geologists'works, geomorphologists had investigated the fault topography of Japan. By these studies, it had become clear before the War II that there are many fault scarps and fault valleys in this country, which have been produced probably by Quaternary faulting. Tsujimura, T. (1932) published a distribution map of topographically-recognized faults, in which 413 fault systems were registered.Recently, the geological and geomorphological studies have been jointly performed and the movement-history of some active faults in Quaternary time are clarified quantitatively (Table 1). It is also shown that many active faults hitherto considered to have only vertical displacement are strike-slip faults accompanied by lesser dip-slip components. The Atera fault (Sugimura & Matsuda, 1965), the Atotsugawa fault (Matsuda, 1966), and the Median Tectonic line (Kaneko, S., 1966; Okada, A., 1968), which was described recently, are examples.Some features of the active strike-slip faults described from Japan may be summerized as follows:A number of active faults or fault zones are present particularly in central Japan (the Chubu, Kinki, and Shikoku districts). They are, however, less than one hundred kilometers in length and a few kilometers in total displacement of the basement rocks, except for the Median Tectonic line (and probably the Itoigawa-Shizuoka Tectonic line).There is a marked regularity in the fault systems of the central Japan between the trend of faults and the sense of the displacement: the NW-trending faults are left-lateral, whereas the NE-trending faults are right-lateral. This implies that the earth's crust of the region is under the same stress system having the maximum (compressional) principal axis of approximate east-west.

24. Coincidence of the direction of maximum pressure deduced from structure of volcanoes and active strikeslip fault system(Abstracts of Papers submitted for the Meetings of the Society)

24. Coincidence of the direction of maximum pressure deduced from structure of volcanoes and active strikeslip fault system(Abstracts of Papers submitted for the Meetings of the Society)