Showing papers on "Fault (geology) published in 1975"
TL;DR: In this article, two recent and three historical earthquakes which occurred along the Nankai trough, marking the northern plate boundary between the Philippine Sea and the Asian Plate, are studied mainly on the basis of the data of crustal deformations and tsunami waves.
995 citations
TL;DR: The dilatancy/fluid-diffusion mechanism for shallow earthquakes is a consequence that considerable volumes of fluid are rapidly redistributed in the crust following seismic faulting as discussed by the authors, which is borne out by the outpourings of warm groundwater which have been observed along fault traces following some moderate (M5-M7) earthquakes.
Abstract: A consequence of the dilatancy/fluid-diffusion mechanism for shallow earthquakes is that considerable volumes of fluid are rapidly redistributed in the crust following seismic faulting. This is borne out by the outpourings of warm groundwater which have been observed along fault traces following some moderate (M5–M7) earthquakes. The quantities of fluid involved are such that significant hydrothermal mineralisation may result from each seismically induced fluid pulse, and the mechanism provides an explanation for the textures of hydrothermal vein deposits associated with ancient faults, which almost invariably indicate that mineralisation was episodic.
641 citations
TL;DR: In this paper, structural analysis shows that the formation of wrench-faults was related with a N-S to NW-SE compression, and two blocks may be distinguished by the Permian in the western European plate: a northern block and an Ibero-Corso-Sardic block.
308 citations
TL;DR: The geologic history of late Quaternary faulting is the most promising source of statistics on frequencies and locations of large shocks as mentioned in this paper, and the geologic record is a far more valuable tool in estimating seismicity and associated seismic hazard than has generally been appreciated.
Abstract: This paper argues that the geologic record, and the late Quaternary history in particular, is a far more valuable tool in estimating seismicity and associated seismic hazard than has generally been appreciated. Those parts of the world with the longest historic records of earthquakes — some 2,000 yr for Japan and the Middle East and 3,000 yr for China — are the areas that should give us the greatest pause in using historic records for extrapolations, because earthquakes in these regions show surprisingly large long-term temporal and spatial variations. The very short historic record in North America should, therefore, be used with extreme caution in estimating possible future seismic activity. The geologic history of late Quaternary faulting is the most promising source of statistics on frequencies and locations of large shocks. Seismotectonic relationships in California, where the one-to-one correlation between large earthquakes and active faults is well documented, also apply to other parts of the world to a greater extent than has generally been recognized. The same is true for the frequent evidence of surface faulting associated with both large and small shallow earthquakes. The long history of Turkish earthquakes illustrates marked temporal changes in spatial distribution of seismicity, but all major seismic areas in Turkey could easily have been identified even in the absence of historic records by field studies of Quaternary faulting. Central Japan has so many Quaternary faults that seismic hazard must be considered relatively uniform and widespread. It is disconcerting that some of the largest Japanese earthquakes have occurred on seemingly innocuous faults; conversely, some of the largest and most spectacular faults, such as the Median Tectonic Line and the Itoigawa-Shizuoka Tectonic Line, have caused no major earthquakes within the historic record. Abundant evidence of Quaternary and probable Holocene displacements on these two faults, however, suggests that they are likely sources for future large events. China likewise shows close association between active faults and major earthquakes; perhaps in no other part of the world are Quaternary faults more spectacular. A segment of the Philippine fault that was the locus of a recent large earthquake demonstrates that major active faults can be identified adequately in the field even in areas of tropical vegetation. Throughout the world, thrust faults present a special problem in seismic hazard evaluation, because their configurations and degrees of activity are more difficult to determine in the field than those of strike-slip and normal faults. Particularly for thrust faults, trenching and bore-hole techniques are essential exploration tools. The most important contribution to the understanding of long-term seismicity, which is critical to the siting and design of safe structures and to the establishment of realistic building codes, is to learn more — region by region — of the late Quaternary history of deformation.
185 citations
TL;DR: In this paper, the authors investigated the source mechanisms of large earthquakes occurring along the eastern margin of the Japan Sea and determined the parameters for the dislocation on the basis of the long-period surface waves and the tsunami heights at the coasts.
124 citations
TL;DR: In this article, the seismic moment is determined straightforwardly from the fault size alone, and the uncertainty in the method presented here is much less than that in estimating moments from the earthquake magnitude.
Abstract: Large earthquakes on the Pacific coast are characterized, on the average, by σ≈30 bars and L≈2w independently of the size, where σ is the stress drop, L is the fault length, and w is the fault width. It follows from these that the seismic moment is determined straightforwardly from the fault size alone. Such a convenient method of estimation of the seismic moment is also applicable to the major earthquakes in the Japanese islands which are characterized, on the average, by σ≈60 bars and L≈2w. These results can be used for reliable assignment of moment to future large earthquakes as well as historical large earthquakes for which detailed mechanism studies cannot be made. The uncertainty in the method presented here is much less than that in estimating moments from the earthquake magnitude.
109 citations
TL;DR: In this article, an exact solution of elasticity in an infinite elastic rock medium around magma reservoirs of various aspect ratios and the criteria of rock fracturing provide an important tool for the interpretation of the origin and nature of distribution of many ore-bearing fracture systems around magmatic bodies in the world.
Abstract: An exact solution of three-dimensional theory of elasticity in an infinite elastic rock medium around magma reservoirs of various aspect ratios and the criteria of rock fracturing provide an important tool for the interpretation of the origin and nature of distribution of many ore-bearing fracture systems around magmatic bodies in the world. Theoretical analyses suggest the conditions and regions of formation of (1) dominant radial fractures, (2) dominant concentric fractures or combination of radial and concentric fractures, and (3) central subsidence (or graben) in domal uplift related to intrusions of magma bodies of various shapes and sizes. The relations of these fracture systems to the deposition of ore-bearing fluids are discussed in the light of excess magma and hydrothermal fluid pressures. Caldera subsidence and dominant concentric fractures, such as in the San Juan Mountains mining district in Colorado, are, according to our analyses and interpretations, related to intrusion(s) of vertically elongated magma cupolas and high magma and hydrothermal fluid pressures. This differs from Anderson's original contention (1936) that caldera subsidence and outward-dipping ring fractures are due to lower relative magma pressure than lithostatic pressure. Wedging action of magma immediately above a vertically elongated prolate magma body is suggested as a cause of central graben bounded by funnel-shaped normal faults over wide domal uplift. Displacement along normal faults causes underground subsidence above magma cupolas. Extension of such faults close to the surface and displacement along them can produce surface caldera subsidence. Vein-type deposits commonly associated with funnel-shaped felsic (rhyolitic) bodies may be related to near-surface caldera subsidence. The origin of arcuate zones of breccia pipes such as in Silverton cauldron, Colorado, appears to be related to axial symmetric stress condition (s) due to vertically elongated magma body at depth. Estimation of stress distribution around spheroidal and prolate magma bodies suggests development of possible zonal distribution of fractures from the periphery of the magma outward in the order of (1) continuous tension fracture zone, (2) brittle fault zone, (3) ductile fault zone followed by no fault zone. Brittle fault and continuous tension fracture zones provide excellent sites for ore mineral localization. The zonal distribution of fractures also suggests, in a general way, mode of origin and possible extent of distribution of various fracture types, hydrothermal zoning, and their alterations.
109 citations
TL;DR: The amount and distribution of seismic slip along 240 km of the San Jacinto fault zone between Cajon Pass and Superstition Mountain has been obtained from determinations of seismic moment and estimates of source dimension for each of the nine moderate earthquakes as discussed by the authors.
Abstract: The amount and distribution of seismic slip along 240 km of the San Jacinto fault zone between Cajon Pass and Superstition Mountain has been obtained from determinations of seismic moment and estimates of source dimension for each of the nine moderate earthquakes (6 < M < 7) which have occurred there since 1890.
There are two significant gaps in seismic slip, one between Cajon Pass and Riverside, the other from Anza to Coyote Mountain. Each is about 40 km long and both are characterized by complex fault zones and a currently high level of minor seismicity (M < 5). No aseismic fault creep has been identified on either segment. These gaps may mark the sites of the next moderate earthquakes (M = 6 → 7) to occur along the San Jacinto fault zone. The two remaining sections of the fault, Riverside and Anza, and Coyote Mountain to Superstition Mountain, may have been ruptured along their entire lengths, in 1890–1923 and 1942–1968, respectively.
93 citations
TL;DR: In this paper, an 18km-long segment of bed rock of the Dasht-e Baȳaz earthquake fault was studied in detail to define the 1968 earthquake-related and earlier tectonic deformations.
Abstract: An 18-km-long segment of bed rock of the Dasht-e Baȳaz earthquake fault was studied in detail to define the 1968 earthquake-related and earlier tectonic deformations. Ground displacements that accompanied the earthquake coincided precisely with the pre-existing east-trending fault trace. Maximum components of offset were 4 m left-lateral and 1 m south side relatively down. The bedrock displacement occurred along new tension fractures that strike on average at 50°, as well as along reactivated pre-existing structures. Earlier tectonic deformation also produced tension fractures (post-Pliocene), conjugate shears (Pliocene), and tension joints (pre-Pliocene), and all are consistent with 47° to 55° tectonic compression. The study covered three points: (1) the 40° to 45° angle measured between the major principal stress direction indicated by the earthquake fractures and the fault; (2) the apparent constancy of the stress field direction during the three early phases and the 1968 deformation; and (3) the “gap” and “anti-Riedel” structure shown by the overall fault trace, which, we suggest, are characteristic of situations of kinematic restraint and are associated with a nonuniformly propagating rupture.
89 citations
TL;DR: In this paper, the location and the mode of faulting in this earthquake are hypothesized in reference to the source mechanisms of the recent and historical earthquakes there, and the fault parameters are as follows: dip direction: N30°W; dip angle: 25°; fault dimension : 100 km × 70 km; dislocation: 4 m (reverse dip-slip: 3.8 m; right-lateral strike-slips: 1.3 m).
87 citations
TL;DR: In this article, a sinistral rotation of about 60° of the axes of the strain ellipse relative to the crust of Central Europe seems evident, and it is assumed that the rotation is a consequence of the mid-Tertiary rotation of microplates in the Mediterranean.
TL;DR: In this paper, the authors studied the aftershocks of the February and March 1972 San Andreas and San Benito earthquakes and found that the distribution of aftershock source areas progressively expanded during the course of the aftershock sequence, and that the transfer of horizontal, dextral displacement from the San Andreas fault to the Paicines and Calaveras faults within the Bear Valley region.
Abstract: The earthquake sequence of late February and March 1972 involved movement along the San Andreas fault and within the crustal wedge enclosed by the branching San Andreas and San Benito faults near Bear Valley, San Benito County, California. Activity was mainly confined to three distinct zones of strike-slip faulting: the short north-trending aftershock zone of the M 3.5 earthquake of February 22, 1972, the aftershock zone of the M 5.0 Bear Valley earthquake of February 24, 1972 located along the San Andreas fault, and the west-trending aftershock zone of the M 4.6 earthquake of February 27, 1972. The north-trending and west-trending zones lie between the two major splays of the branching fault system. Focal mechanism solutions from events in these zones are consistent with the transfer of horizontal, dextral displacement from the San Andreas fault to the San Benito, Paicines and Calaveras faults within the Bear Valley region. During the 18 months preceding the February 1972 sequence, the hypocentral regions of both the M 5.0 and M 4.6 shocks were characterized by concentrations of small earthquakes. Aftershock source areas of these two events progressively expanded during the course of the aftershock sequence. Estimates of the mainshock rupture surface for these events based on the distribution of aftershocks range over a factor of 4 owing to the irregular distribution of aftershocks and the rapid growth of the aftershock zone.
TL;DR: In this paper, an earthquake sequence along a section of the San Andreas fault near Bear Valley, California (February-March 1972) reveals large velocity changes in the vicinity of the fault.
Abstract: Intensive study of an earthquake sequence along a section of the San Andreas fault near Bear Valley, California (February-March 1972) reveals large velocity changes in the vicinity of the fault. These velocity changes are caused primarily by structural variations in the vicinity of the fault zone but may represent in part the effect of active tectonic processes.
TL;DR: The Bright Angel and Eminence faults trend northeastward for approximately 60 mi (100 km) through the eastern Grand Canyon region as mentioned in this paper, and the first record of movement indicates that it was reverse; it coincided with the deposition of the basal Shinumo Quartzite.
Abstract: The Bright Angel and Eminence faults trend northeastward for approximately 60 mi (100 km) through the eastern Grand Canyon region. The Bright Angel fault parallels basement foliation. Activity along the fault dates from Precambrian time. The first record of movement indicates that it was reverse; it coincided with the deposition of the basal Shinumo Quartzite. Additional reverse movement occurred following intrusion of the Unkar Group by diabase sills and dikes resulting in a total of as much as 1,300 ft (400 m) of displacement, east side up. The Precambrian Chuar Group was later broken by a series of northwest-trending normal faults that tilted the section toward the northeast, causing minor adjustments along the Bright Angel fault. Possible reverse movement along the Bright Angel fault is recorded in a local angular unconformity between the Paleozoic Redwall and Supai Formations. East-dipping Laramide (?) monoclines developed as reverse movement occurred along selected preexisting northwest-trending Precambrian faults. Tensional faulting beginning in Miocene (?) or Pliocene (?) time caused downfaulting, east side down, along the Bright Angel fault. The Eminence fault, west side down, is part of a graben complex.
TL;DR: In this paper, a major geophysical lineament in Ireland is correlated with the Highland Boundary fault in Scotland; it is shown to separate a southern block, deformed in Middle to Late Cambrian time, from a northern block that was formed in early Ordovician time.
Abstract: A major geophysical lineament in Ireland is correlated with the Highland Boundary fault in Scotland; it is shown to separate a southern block, deformed in Middle to Late Cambrian time, from a northern block that was deformed in early Ordovician time.
TL;DR: The Channel consists of three distinct provinces each characterized by its own geological style as discussed by the authors, the Central Province is dominated by three fault or monoclinal structures and has rocks ranging from Jurassic to Eocene age, the Eastern Province is a relatively stable area dominated by a Tertiary syncline and a continuation of the Wealden anticline.
Abstract: The Channel consists of three distinct provinces each characterized by its own geological style. The Western Province has rocks ranging in age from Lower Palaeozoic to Miocene with marked unconformities beneath the Upper Cretaceous and the Eocene strata. A major tectonic feature is a line of faults extending east-northeast up Channel. The Central Province is dominated by three fault or monoclinal structures and has rocks ranging from Jurassic to Eocene age. The Eastern Province is a relatively stable area dominated by a Tertiary syncline and a continuation of the Wealden anticline. Events related to the development of oceanic crust in Permian times are believed to have caused basic igneous activity, rifting and crustal thinning in the Western Channel and these factors and the subsequent opening of the Atlantic exerted a control over the development of the Channel. Alpine tectonism led to renewed movement on some structures. Folds are thought to be the surface expression of movements on old fault planes. The importance of a tectonic line between the Isle of Wight and northern France is emphasized.
TL;DR: In this paper, a fault pattern has been mapped in plan view on part of the Nile cone by means of long-range (13 km) side-scan sonar, interpreted with the aid of air-gun profiles as consisting of a belt of normal faults, the largest of which define the upslope edges of complex grabens, and some of which are growth faults.
Abstract: A fault pattern has been mapped in plan view on part of the Nile cone by means of long-range (13 km) side-scan sonar. It is interpreted with the aid of air-gun profiles as consisting of a belt of normal faults, the largest of which define the upslope edges of complex grabens, and some of which are growth faults. The orientation and structure of many of the grabens suggest an origin due to mass downslope movement and diapirism. It is possible, however, that the location of the belt of faulting was controlled by a more deep-seated tensional force related to a north-northeast movement of the Sinai block, particularly as some of the faults have a northwest trend parallel to the Gulf of Suez rift. Other observed features are meandering channels and broad patches of contrasting acoustic surface reflectivity consisting of low rises with small-scale roughness separated by hollows that are floored by smooth-surfaced soft mud.
TL;DR: A relatively detailed investigation of the mid-Atlantic ridge crest at 26°N was conducted by using narrow-beam bathymetric data, total earth's magnetic field measurements, and underwater photographs.
Abstract: A relatively detailed investigation of the Mid-Atlantic Ridge crest at 26°N was conducted by using narrow-beam bathymetric data, total earth's magnetic field measurements, and underwater photographs. The Mid-Atlantic Ridge crest at 26°N appears to be hydrothermally active. The structural setting of this area is conducive to the occurrence of hydrothermal deposits. The walls of the rift valley are extensively faulted with blocks and steps ranging in size from kilometers to meters in width and relief. Underwater photographs show hydrothermal manganese associated with interpreted fault steps at depths between 3100 and 2500 m on the east wall, suggesting that the faults provide avenues for hydrothermal fluids. Small topographic highs in the floor of the rift valley are the sites of relatively recent volcanism and are believed to represent the top of an active dike emplacement zone. Bathymetric trend directions for this portion of the ridge crest are complex in comparison with plate rotation predicted trends for the Mid-Atlantic Ridge. The bathymetric grain is a function of processes active in the rift valley.
TL;DR: A dense seismograph network in the Imperial Valley recorded a series of earthquake swarms along the Imperial and Brawley faults and a diffuse pattern of earthquakes along the San Jacinto fault.
Abstract: A dense seismograph network in the Imperial Valley recorded a series of earthquake swarms along the Imperial and Brawley faults and a diffuse pattern of earthquakes along the San Jacinto fault. Two known geothermal areas are closely associated with these earthquake swarms. This seismicity pattern demonstrates that seismic slip is occurring along both the Imperial-Brawley and San Jacinto fault systems.
TL;DR: The median valley can be divided into four provinces: the outer walls, terraces, inner walls, and floor as discussed by the authors, and block faulting along normal faults with as much as 600 m throw is the dominant mechanism for creating median-valley relief.
Abstract: Near-bottom geophysical observations made over the median valley of the Mid-Atlantic Ridge near lat 37°N show that the median valley can be divided into four provinces: the outer walls, terraces, inner walls, and floor. Block faulting along normal faults with as much as 600 m throw is the dominant mechanism for creating median-valley relief, particularly at the inner and outer walls. Most of these faults dip toward the median-valley axis an average of 45°. Many of the block tops slope 3° to 10° away from the valley axis. Some of the major fault scarps are linear for more than 20 km. Large-scale block faulting occurs less than 1 km from the axis of spreading. Inversion of near-bottom magnetic anomalies suggests that the principal zone of intrusion may be no wider than 1 to 2 km and is along the valley axis. This spreading center is marked by either a central ridge or central depression, which suggests either discrete magma sources or discrete taps of a linear source beneath the median-valley axis. The central ridge is a volcanic construction, although faulting and (or) volcano-tectonic uplift may contribute to its relief.
TL;DR: In this paper, the source mechanism of the Saitama earthquake (36.07°N,139.40°E, M s = 5.4) of July 1, 1968, is studied on the basis of P-wave first motion, aftershock, long-period surface-wave data and low-magnification longperiod seismograms recorded in the nearfield.
TL;DR: In this paper, the fundamental-mode Rayleigh waves for the Koyna earthquake of December 10, 1967 recorded on long-period vertical component seismograms of 30 WWSSN stations have been Fourier analyzed.
Abstract: The fundamental-mode Rayleigh waves for the Koyna earthquake of December 10, 1967 recorded on long-period vertical component seismograms of 30 WWSSN stations have been Fourier analyzed. The radiation patterns have been plotted at six wave periods. Comparison of these data with the theoretical radiation patterns computed for various fault parameters favored the strike of the fault in N10°E direction, dip 78°W, slip 175°, and the depth of focus to be 10 km. Strike-slip faulting on a near-vertical fault plane has been inferred. The S -wave polarization angles, which have been obtained for 13 stations, also favor the above solution. Surface-wave magnitude has been determined to be 6.3 and the fault surface area to be 252 km 2 . Using the Rayleigh-wave spectral amplitude for 50-sec period, the seismic moment, M o , is determined to be 0.82 × 10 26 dyne-cm. The values of average dislocation, seismic energy, apparent stress, and apparent strain are calculated to be 108 cm, 2.25 × 10 21 ergs, 15.4 bars and 5.3 × 10 −5 , respectively. For a rupture velocity of 1.5 km/sec, the values of fault length and stress drop are found to be about 23 km and 19.8 bars, and for a rupture velocity of 3.0 km/sec these values are about 40 km and 6.2 bars, respectively.
TL;DR: In this article, the authors applied Joint Hypocenter Determination (JHD) to carefully determined arrival time data from a small network of sensitive and well-distributed local and teleseismic stations.
Abstract: Application of the method of Joint Hypocenter Determination (JHD) to carefully determined arrival time data from a small network of sensitive and well-distributed local and teleseismic stations provides very precise locations of deep earthquakes. The precision of locations attained by this method—the relative locations are good to about 5 km—is limited mainly by the accuracy and precision of the measurements of arrival times. Application of the technique to a small and very active part of the deep earthquake zone of the Tonga island arc (depths near 600 km) reveals probable fault planes associated with the occurrence of deep earthquakes. The spatial distribution of precisely relocated hypocenters is closely related to the orientation of the focal mechanism solutions of two deep earthquakes. Hypocenters cluster in a plane parallel to one of the nodal planes for each of the two solutions examined. The planar features are yearly vertical and have linear dimensions of about 40 km. In one case the shocks defining the fault plane also tended to cluster in time near the occurrence of the largest event. These and other data suggest the existence of several distinct fault planes in the area studied. Our study is being extended to examine the structure of the entire Tonga deep seismic zone.
TL;DR: The San Simeon-Hosgri fault has been identified as a possible extension of the Morro-Islay Hill in coastal central California by Hoskins and Griffiths.
Abstract: There has been 80 kilometers or more ofright slip along the late Quaternary San Simeon-Hosgri fault system of coastal California during the last 5 to 13 million years. Part ofan oil-rich basin is probably offset by this fault system, and the system may be a potential hazard to nearby structures. Comparison of stratigraphic sections exposed on opposite sides of the late Quaternary San Simeon-Hosgri fault system at Point Sal and near San Simeon (Fig. 1) strongly suggests large-scale lateral displacement. The nature and age of strikeslip displacement along the fault system has important economic and environmental implications, for it suggests the possible location of an offshore extension of the oilproducing Santa Maria basin and indicates that the system poses a potential hazard to engineered facilities. The San Simeon fault in coastal central California, first named in 1974 (1), can be traced on land for a distance of approximately 19 km-that is, from Ragged Point to San Simeon Point (Fig. 2). In the area offshore from Ragged Point, Hoskins and Griffiths (2) show a 65-km northwestward extension of the San Simeon fault. Silver (3) reports a fault with as much as 5 km of dip separation in the offshore basin south of Point Sur (that is, 80 km north of San Simeon), which may be the northern extension of the San Simeon fault. The San Simeon fault may also extend farther south from San Simeon Point to near Point Estero (Fig. 1) in the offshore, as postulated by others (1). Such a suggestion is supported by the fact that the coastline is straight and rises abruptly from the sea. Near San Simeon Point the trace of the San Simeon fault is concealed by late Pleistocene or Holocene slightly cemented dune sand deposits. It faults the 122-m Pleistocene terrace approximately 5 km northeast of Point Piedras Blancas, but does not cut the 12-m terrace near either Breaker Point or Ragged Point. The Arroyo Laguna fault (Fig. 2) is believed to be a relatively younger and more recently active strand of the San Simeon fault zone. This fault is marked by a pronounced linear valley north of San Simeon Point (4), by a 75-m fault scarp, and by faulting of the 122-m Pleistocene terrace. 26 DECEMBER 1975 The fault crosses several westor southwest-draining canyons, including Arroyo Hondo, Arroyo de los Chinos, and three other unnamed canyons between Arroyo de los Chinos and Arroyo de la Cruz (4). Each canyon is marked by right lateral deviation of 150 to 450 m; however, the fault does not juxtapose markedly different rock sequences or types (Fig. 2) as does the San Simeon fault. The San Simeon fault terminates the Arroyo del Oso fault, which cuts through the lower part of the 12-m terrace (1, 4). The Pleistocene terrace deposits within the region are 130,000 + 30,000 and 140,000 ± 20,000 years old (5); therefore the Arroyo del Oso fault is younger than approximately 130,000 years and, at least in part, the San Simeon fault must be still younger. An epicenter (date unrecorded) is located on the Arroyo del Oso fault and the magnitude of the earthquake is reported to have been between 4.0 and 4.4 (6). Holden (7) reports earthquakes of 26 October or 26 November 1852 and 1 February 1853 at San Simeon, where \"houses were injured.\" However, the authenticity of these early Fig. 1. Location of the San Simeon-Hosgri fault system. Base map is from Jennings (11) and several other sources (1, 2, 4, 9, 10, 13). Spots indicate hypabyssal plugs of the Morro Rock-Islay Hill complex (1, 10, 17).
TL;DR: In this paper, a 22 km long segment of the still active North Anatolian fault zone has been studied and the main fault can be observed clearly in the field and on aerial photographs, and it trends 105° in the mapped area.
TL;DR: In this paper, a composite fault-plane solution was proposed for large shocks at Fairview Peak and Rainbow Mountain in 1954, which showed that the same regional stress field is acting to produce earthquakes in both areas.
Abstract: Seismicity in the Excelsior Mountains area appears to have been an order of magnitude higher for at least several decades than that which preceded great earthquakes in central Nevada in 1915 and 1954. A high degree of crustal fracturing is indicated for this area by complex geology and by a scattered distribution of epicenters. A composite fault-plane solution is similar to those for large shocks at Fairview Peak and Rainbow Mountain in 1954, which shows that the same regional stress field is acting to produce earthquakes in both areas. The slope of the recurrence curve, or b value, is higher than average for the Nevada region. Crustal strains recorded at Mina indicate that periods of strain build-up alternate with periods of strain release. Comparison of these characteristics with results of laboratory experiments and observations in other regions suggests that the area is one in which a moderate level of tectonic stress combined with a high degree of crustal fracturing leads to strain release by a continuing series of small-to-moderate earthquakes and fault creep. If so, the magnitude of 6¼ for the 1934 Excelsior Mountains earthquake may represent a maximum magnitude for this area.
TL;DR: Geologically young displacements have been observed along 24 faults in an area of Alaska of approximately 624,000 km 2. Active faults of southern Alaska include the Patton Bay and Hanning Bay reverse-slip faults, both reactivated in 1964 as mentioned in this paper.
TL;DR: The structural closures on the down-thrown side of such faults are asymmetric and increase in amplitude with depth as discussed by the authors, and the vertical profiles of these faults describe hyperbolic curves which tend to f attenuate with depth.
Abstract: Tertiary sediments of the Burgos basin of northeastern Mexico are broken abundantly by faults which are of two types, namely, growth and postdepositional. The growth faults have a sinuous, north-south trend, and are many kilometers in length. Collectively, they make up a series of subparallel blocks of sediments which are faulted in a down-to-basin direction. Although these sediments thicken basinward, they also commonly exhibit rollover (reverse drag) on the downthrown side. In addition, they commonly thicken locally in the opposite direction in close proximity to the growth faults. The structural closures on the downthrown side of such faults are asymmetric and increase in amplitude with depth. Vertical profiles of these faults describe hyperbolic curves which tend to f atten with depth. Bruce pointed out that such faults in the Texas coastal area "flatten and converge at depth to planes related to fluid pressure and form the seaward flanks of underlying shale masses." He also stated that such "faults formed during time of shoreline regression were developed primarily through differential compaction of adjacent sedimentary masses. These faults die out at depth near the depoaxes of the sandshale section." Postdepositional faults are more numerous than the growth faults, more closely spaced, and generally have less throw. Their distinguishing characteristic is that the sedimentary section on either side of a postdepositional fault is of the same thickness, whereas the sediments on the downthrown side of a growth fault are always thicker than their counterpart on the upthrown side. Structural closures on the downthrown side of a growth fault afford ideal conditions for hydrocarbon entrapment. Multiple reservoir sandstones are present. They may consist of one or more crescent to "halo-like" bar sands which were deposited around a growth structure or an isolated sand lens on top of the structure. In rare cases a deltaic-distributary system of sandstones is present in the uppermost part of the stratigraphic sequence of sandstones where the structural closure is minimal.
TL;DR: In this article, a 2-component tiltmeters have been installed in shallow boreholes along 85 km of the currently most active section of the San Andreas fault in the western United States.
Abstract: The continuous monitoring of surface deformation near active faults is clearly necessary for an understanding of elastic strain accumulation and elastic and anelastic strain release associated with earthquakes. Fourteen 2-component tiltmeters have been installed in shallow boreholes along 85 km of the currently most active section of the San Andreas fault in the western United States. These instruments operate at a sensitivity of 10−8 radians. Five of these tiltmeters, extending along one 35 km section of the fault, have been in operation since June 1973. The results indicate that regional tectonic tilting has occurred before more than ten individual earthquakes or groups of earthquakes with epicenters within ten earthquake source dimensions of one or more instruments. This tilting has a time scale of up to a month depending on earthquake magnitude. The amplitude of these tilts exceeds by almost an order of magnitude that expected from a dislocation model of the source using seismically determined parameters. No indication of rapid or accelerated tilt just prior to these earthquakes has been seen.