Total Slip Research Articles

Predictive model of San Andreas fault system paleogeography, Late Cretaceous to early Miocene, derived from detailed multidisciplinary conglomerate correlations

Paleogeographic reconstruction of the region of the San Andreas fault system in western California, USA, was hampered for more than two decades by the apparent incompatibility of authoritative lithologic correlations. These led to disparate estimates of dextral strike-slip offsets across the San Andreas fault, notably 315 km between Pinnacles and Neenach Volcanics, versus 563 km offset between Anchor Bay and Eagle Rest peak. Furthermore, one section of the San Andreas fault between Pinnacles and Point Reyes had been reported to have six pairs of features showing only ~ 30 km offset, while several younger features in that same area were reported consistent with ~ 315 km offset. Estimates of total dextral slip on the adjoining San Gregorio fault have ranged from 5 km to 185 km. Sixteen Upper Cretaceous and Paleogene conglomerates of the California Coast Ranges, from Anchor Bay to Simi Valley, were included in a multidisciplinary study centered on identification of matching unique clast varieties, rather than on simply counting general clast types. Detailed analysis verified the prior correlation of the Upper Cretaceous strata of Anchor Bay at Anchor Bay with a then-unnamed conglomerate at Highway 92 and Skyline Road (south of San Francisco); and verified that the Paleocene or Eocene Point Reyes Conglomerate at Point Reyes is a tectonically displaced segment of the Carmelo Formation of Point Lobos (near Monterey). The work also led to three new correlations: Point Reyes Conglomerate with granitic source rock at Point Lobos; a magnetic anomaly at Black Point (near Sea Ranch) with a magnetic anomaly near San Gregorio; and strata of Anchor Bay with previously established source rock, the potassium-poor Logan Gabbro of Eagle Rest peak, at a more recently recognized subsurface location just east of the San Gregorio fault, south of San Gregorio. From these correlations, a Late Cretaceous to early Oligocene paleogeography was constructed which was unique in utilizing modern shapes of tectonic blocks in a paleogeographic resolution synthesizing both the proposed 315 and ~ 30 km San Andreas fault offsets, as well as honoring the lithologic correlation of Anchor Bay with Eagle Rest peak. The model has proved predictive. Since its first introduction, in April and June 1998, other authors have reported seven subsequently identified correlative pairs of geological and geophysical features consistent with it. These required both lateral and temporal expansion of the model: The paleogeography now incorporates 58 pairs of correlative features, covers the period from 70 to 21.3 Ma, and extends from Pelona and Orocopia to the Mendocino triple junction. The model supports the view that fault is not the boundary between the Pacific and North American plates is a wide zone encompassing the San Andreas fault system. However, the model suggests the San Andreas fault is a temporary assemblage of separate segments having different motions, and is neither the primary plate boundary, nor the dominant fault of the San Andreas fault system. By improving resolution of complex spatial–temporal distribution of slip along this evolving tectonic margin, the model provides a firmer foundation for resolution of geophysical issues such as slab window and Pacific Plate subduction models.

Grain Size Effect in Sheet Metal Microforming Simulation Adopting Strain Gradient Concept

A strain gradient dependent crystal plasticity approach is adopted to model the size effect in the microforming process of sheet metal. To take into account the grain size effect in the simulation, the total slip resistance in each active system was assumed to be due to a mixed population of forest obstacles arising from both statistically stored and geometrically necessary dislocations. The non-local crystal plasticity has been established by directly incorporating the above slip resistance into the conventional rate-dependent crystal plasticity and implemented into the Abaqus/Standard FE platform by developing the user subroutine UMAT. The formulation has been recapitulated and followed by presentation of the numerical examples employing both the local and non-local formulation. The comparison of the counterpart simulation results reveals the grain size effect in the microforming process and demonstrates the availability of the code developed.

Stateline fault system: A new component of the Miocene-Quaternary Eastern California shear zone

The Eastern California shear zone is an active, north-northwest–trending zone of intraplate right-lateral shear that absorbs ∼25% of Pacific-North America relative plate motion. The Stateline fault system (SFS), which includes several previously recognized, discontinuously exposed Quaternary structures along the California-Nevada border, is in this paper defined as a continuous, 200-km–long zone of active dextral shear that includes (from south to north) the Mesquite, Pahrump, and Amargosa Valley segments. Recognition of this system expands the known extent of the Eastern California shear zone ∼50 km to the east-northeast from its traditionally recognized boundary along the Death Valley fault system. Proximal volcanic and rock avalanche deposits offset across the Mesquite segment of the SFS indicate 30 ± 4 km of slip on this structure since 13.1 ± 0.2 Ma. This offset is an order of magnitude larger than previous estimates across this section of the SFS, but it is consistent with larger offsets previously proposed for the central and northern sections. The total offset and averaged slip rate since mid-Miocene time (2.3 ± 0.35 mm/yr) are similar to those of other major faults across this portion of the Basin and Range, which, from east to west, include the Death Valley, Panamint Valley-Hunter Mountain, and Owens Valley fault systems. However, in contrast to these faults, the average post–mid-Miocene slip rate on the SFS is approximately twice that estimated from present-day geodetic observations and an order of magnitude greater than estimates of average post–mid-Pleistocene slip rates. This discrepancy between long-term, short-term, and geodetically derived slip rates differs from other geologic-geodetic, slip-rate discrepancies in the Eastern California shear zone, where geodetic slip rates are significantly faster than both long-term and short-term geologic slip rates. This suggests that either the slip rate on the SFS has diminished over time, such that the system is an abandoned strand of the relatively young Eastern California shear zone, or that the present-day slip rate represents a transient period of slow slip, such that strands of the shear zone must accommodate a complex spatial and temporal distribution of slip.

Fretting Wear Behavior of Cu–Al Coating on Ti-6Al-4V Substrate under Dry and Wet (Lubricated) Contact Condition

The fretting wear behavior of Cu–Al coating was investigated with and without fatigue load under the dry and wet (lubricated) contact conditions. The Cu–Al coating was plasma deposited on titanium alloy, Ti-6Al-4V. Fretting regime was determined from the shape of fretting hysteresis loop. Fretting regime changed from partial slip to total (gross) slip at ∼15 μm of the applied relative displacement, and this transition point was independent of fatigue loading and contact surface (lubricated versus dry) conditions. Wet contact condition reduced frictional force during cycling, as evidenced by the lower-tangential force. Wear analysis using the accumulated dissipated energy approach did not show any effect of contact surface condition. In other words, the relationship between the accumulated dissipated energy and wear volume showed a linear relationship, and it was independent of loading and contact surface conditions, as well as of the fretting regime. Further, the relationship between the wear depth and accumulated dissipated energy did not show any effect of loading and contact surface conditions, as well as of the fretting regime up to instant when the maximum wear depth was equal to the coating thickness.

Cosmogenic 10Be and 36Cl geochronology of offset alluvial fans along the northern Death Valley fault zone: Implications for transient strain in the eastern California shear zone

The northern Death Valley fault zone (NDVFZ) has long been recognized as a major right‐lateral strike‐slip fault in the eastern California shear zone (ECSZ). However, its geologic slip rate has been difficult to determine. Using high‐resolution digital topographic imagery and terrestrial cosmogenic nuclide dating, we present the first geochronologically determined slip rate for the NDVFZ. Our study focuses on the Red Wall Canyon alluvial fan, which exposes clean dextral offsets of seven channels. Analysis of airborne laser swath mapping data indicates ∼297 ± 9 m of right‐lateral displacement on the fault system since the late Pleistocene. In situ terrestrial cosmogenic 10Be and 36Cl geochronology was used to date the Red Wall Canyon fan and a second, correlative fan also cut by the fault. Beryllium 10 dates from large cobbles and boulders provide a maximum age of 70 +22/−20 ka for the offset landforms. The minimum age of the alluvial fan deposits based on 36Cl depth profiles is 63 ± 8 ka. Combining the offset measurement with the cosmogenic 10Be date yields a geologic fault slip rate of 4.2 +1.9/−1.1 mm yr−1, whereas the 36Cl data indicate 4.7 +0.9/−0.6 mm yr−1 of slip. Summing these slip rates with known rates on the Owens Valley, Hunter Mountain, and Stateline faults at similar latitudes suggests a total geologic slip rate across the northern ECSZ of ∼8.5 to 10 mm yr−1. This rate is commensurate with the overall geodetic rate and implies that the apparent discrepancy between geologic and geodetic data observed in the Mojave section of the ECSZ does not extend north of the Garlock fault. Although the overall geodetic rates are similar, the best estimates based on geology predict higher strain rates in the eastern part of the ECSZ than to the west, whereas the observed geodetic strain is relatively constant.

Independent traction control for uneven terrain using stick-slip phenomenon: application to a stair climbing robot

Mobile robots are being developed for building inspection and security, military reconnaissance, and planetary exploration. In such applications, the robot is expected to encounter rough terrain. In rough terrain, it is important for mobile robots to maintain adequate traction as excessive wheel slip causes the robot to lose mobility or even be trapped. This paper proposes a traction control algorithm that can be independently implemented to each wheel without requiring extra sensors and devices compared with standard velocity control methods. The algorithm estimates the stick-slip of the wheels based on estimation of angular acceleration. Thus, the traction force induced by torque of wheel converses between the maximum static friction and kinetic friction. Simulations and experiments are performed to validate the algorithm. The proposed traction control algorithm yielded a 40.5% reduction of total slip distance and 25.6% reduction of power consumption compared with the standard velocity control method. Furthermore, the algorithm does not require a complex wheel-soil interaction model or optimization of robot kinematics.

A Tactile Sensor for Incipient Slip Detection

This article introduces a new tactile sensor for incipient slip detection. The sensor has concentric circular ridges over its surface and is designed with the aim of differentiating between local slip and total slip. Partial deformation of ridges on the edge of contact with the object exposes built-in fiber optics to ambient light. Changes in light signals are used as an indication of incipient slip. A two-stage computer simulation is presented using finite element, graphics, and image processing software. Experiments reveal an early change in light signals that can be used to ensure the effectiveness of the proposed Sensor.

Reassessment of a Slip Budget along the Parkfield Segment of the San Andreas Fault

Historically, the Parkfield segment has represented a transition in fault behavior along the San Andreas fault (saf). Despite a ∼33 mm/yr long-term slip rate along the saf, slip has not been observed on the Cholame segment since the great 1857 Fort Tejon earthquake. During that time, the Parkfield segment has experienced slip from at least six ∼ M 6.0 earthquakes, aseismic fault creep, and from minor earthquakes. Data from aseismic slip-rate studies and historical earthquake studies allow us to estimate the total slip released along this portion of the saf since 1857. Assuming the saf should slip at the long-term slip rate, a slip deficit of ∼5 m exists along the Cholame segment since 1857. The slip deficit is approximately equivalent to 1857 offsets measured on the Cholame and the southeast portion of the Parkfield segment. Thus, the slip deficit in southeast Parkfield and Cholame may be as great as the slip accommodated along these segments in 1857. The slip deficit abruptly decreases to the northwest across the Parkfield segment. It is < 2 m near the town of Parkfield and ∼0 m northwest of Middle Mountain. An ∼ M 7 event rupturing all or part of the Cholame segment and the southeastern Parkfield segment (slip decreasing to the northwest) would release the accumulated slip and is plausible. Importantly, this study also shows that the change in the pattern of strain release occurs in the middle of the Parkfield segment, rather than at its ends. Online material : Tables showing aseismic and coseismic slip estimations and calculations.

Faulting and extension rate over the last 20,000 years in the offshore Whakatane Graben, New Zealand continental shelf

Oblique rifting in the offshore Taupo Volcanic Zone, New Zealand, is expressed in widely distributed active normal faulting in the 20‐km‐wide Whakatane Graben. Active faults are identified along seafloor scarps and displacements of the post‐last glacial transgressive ravinement surface (&lt;20 ka), using a network of seismic reflection data and multibeam bathymetry. The rifting involves basement blocks back‐tilted by 12–16°, controlled by large NW dipping faults with intersecting antithetic faults within the 3‐km‐thick sedimentary sequence. Faults along the graben border parallel the rift axis, while those in the center are moderately oblique to it. We present a novel method to estimate the age of a postglacial surface (7.5–20.5 ka), with consideration to spatially varying subsidence and uplift, and measure fault throw across &gt;400 faults. We derive an extension rate at seismogenic depths (6–10 km) across the graben of 13 ± 6 mm yr−1, by summing surface measurements, assuming an average crustal fault dip of 45 ± 15°, and correcting for the discrepancies between surface and deep crustal extension estimates. Structural and kinematic data implies an extension direction 20° oblique to the rift axis, resulting in up to 4.6 ± 2.1 mm yr−1of dextral motion parallel to the rift axis. The strike‐slip motion is accommodated by dip‐slip displacements on oblique faults in the center of the graben, and oblique‐slip faulting along the rift margins. Pure dip‐slip in the graben center represents &gt;50% of the total slip, with the Rangitaiki Fault accommodating 25% of the total extension in the graben.

The Gibraltar Arc seismogenic zone (part 2): Constraints on a shallow east dipping fault plane source for the 1755 Lisbon earthquake provided by tsunami modeling and seismic intensity

The Great Lisbon earthquake has the largest documented felt area of any shallow earthquake and an estimated magnitude of 8.5–9.0. The associated tsunami ravaged the coast of SW Portugal and the Gulf of Cadiz, with run-up heights reported to have reached 5–15 m. While several source regions offshore SW Portugal have been proposed (e.g.— Gorringe Bank, Marquis de Pombal fault), no single source appears to be able to account for the great seismic moment as well as all the historical tsunami amplitude and travel time observations. A shallow east dipping fault plane beneath the Gulf of Cadiz associated with active subduction beneath Gibraltar, represents a candidate source for the Lisbon earthquake of 1755. Here we consider the fault parameters implied by this hypothesis, with respect to total slip, seismic moment, and recurrence interval to test the viability of this source. The geometry of the seismogenic zone is obtained from deep crustal studies and can be represented by an east dipping fault plane with mean dimensions of 180 km (N–S) × 210 km (E–W). For 10 m of co-seismic slip an Mw 8.64 event results and for 20 m of slip an Mw 8.8 earthquake is generated. Thus, for convergence rates of about 1 cm/yr, an event of this magnitude could occur every 1000–2000 years. Available kinematic and sedimentological data are in general agreement with such a recurrence interval. Tsunami wave form modeling indicates a subduction source in the Gulf of Cadiz can partly satisfy the historical observations with respect to wave amplitudes and arrival times, though discrepancies remain for some stations. A macroseismic analysis is performed using site effect functions calculated from isoseismals observed during instrumentally recorded strong earthquakes in the region (M7.9 1969 and M6.8 1964). The resulting synthetic isoseismals for the 1755 event suggest a subduction source, possibly in combination with an additional source at the NW corner of the Gulf of Cadiz can satisfactorily explain the historically observed seismic intensities. Further studies are needed to sample the turbidites in the adjacent abyssal plains to better document the source region and more precisely calibrate the chronology of great earthquakes in this region.

Progression of fretting fatigue damage in Ti–6Al–4V

An investigation was conducted to explore the nature of fretting fatigue damage in the stages prior to crack formation. In the unique experimental apparatus employed in this study, where total slip never occurs, several locations on each test specimen exist where cracks can develop due to local contact conditions. Under the test conditions used, not all of the sites had cracks upon test completion. This study evaluated the condition of non-cracked sites on several fretted specimens in an effort to identify differences between these and sites where small cracks were observed. A single test condition of 620 MPa average applied static clamping stress and 250 MPa applied axial fatigue stress for R = 0.5 was selected, which corresponds to a fretting fatigue life of 10 7 cycles based on prior work. For specimens tested to 10 6 cycles, or 10% of life, several destructive and non-destructive characterization methods were chosen: scanning electron microscopy (SEM), residual stress measurement and transmission electron microscopy (TEM). Each site at which crack nucleation could be expected was inspected in the SEM and was then characterized using surface X-ray diffraction to quantify the residual stresses field near that location. Then TEM foils were cut from one area on a specimen with tiny cracks and dislocation densities were observed. A novel technique was used which permitted TEM samples to be obtained from regions in close proximity on the original specimen. Comparisons were made between as-received (AR) and stress-relief annealed (SRA) specimens, on which the stress-relief was applied prior to fretting fatigue testing. SEM inspection was useful for qualitative analysis of wear debris and identification of cracks as small as 20 μm, but was unable to provide quantitative data on the level of fretting fatigue damage beyond crack size. Although differences were noted in the residual stresses for the SRA versus the AR specimens, no residual stress peaks were noted in the edge of contact regions where cracks would eventually develop. TEM observations in the vicinity of the crack nucleation region showed that the dislocation structure decayed rapidly into the specimen thickness. The cause of the dislocations was attributed to plastic deformation caused by the clamping stresses.

Paleoseismology of the southeastern Reelfoot Rift in western Tennessee and implications for intraplate fault zone evolution

The southeastern Reelfoot Rift margin is expressed as a series of collinear scarps across western Tennessee, and shallow S wave reflection profiles, coring, and trenches show late Quaternary faulting along this lineament. At the north end, our seismic profile and coring suggest ≥1.5 m of Wisconsin down‐to‐the‐NW faulting. Coring and trenches across the central lineament show ≥3 m of up‐to‐the‐NW and 8–15 m of right‐lateral Late Wisconsin/Holocene faulting. Averaged late Quaternary right‐lateral slip has been 0.85–0.37 mm/yr on one fault plane at this locality, suggesting that total slip across all southeast rift margin fault planes may accommodate much of the regional strain. Our seismic profile at this site shows up‐to‐the‐west faulting of Eocene strata folded down‐to‐the‐west, indicating structural inversion. Seismic profiles, electrical surveys, coring, and a trench across the southern lineament segment show Holocene faulting. Trenching exposed a vertical fault with ∼0.5 m of late Holocene down‐to‐the‐NW displacement. Nearby, coring and electrical surveys show ∼0.5 m of late Holocene up‐to‐the‐NW faulting. We conclude the southeastern Reelfoot Rift margin is a right‐lateral system with high‐angle faults showing both up‐to‐the‐NW and down‐to‐the‐NW separations. Age constraints permit an earthquake circa 2500 to 2000 years B.P. on the southwestern/central segment of this fault system that ruptured ≥80 km. We suggest the northeastern segment of the southeastern rift margin turned off in Holocene when the Reelfoot step over thrust turned on.

Slip rate and mode of the Feldbiss normal fault (Roer Valley Graben) after removal of groundwater effects

The Feldbiss fault is the main active fault bounding to the southwest the Roer Valley Graben of NW Europe. In order to investigate the reasons of the discrepancy between its short- and long-term slip rate estimates, we have repeatedly surveyed a 2.3 km-long line by levelling at Sittard (The Netherlands) from April 2001 to December 2004. Simultaneously, three superposed aquifers were monitored on both sides of the fault. The across-fault differential groundwater variations are shown to be responsible for a seasonal 0.87 mm/m vertical motion of the fault, mainly through the effect of pore pressure changes in confined aquifers. After removal of this effect, I get a residual trend of −0.60±0.11 mm/yr for the relative motion of the hangingwall. This trend was disturbed in the summer of 2002 by transient millimetre-level up and down motions temporally associated with the small Eschweiler earthquake that occurred on July 22, 2002 on the Feldbiss fault at a distance of 35 km from Sittard. I explain this as a creep event triggered by the passage of trapped seismic waves. The subsisting discrepancy between the long-term slip rate of 0.06 mm/yr and short-term rates of ∼ 1.5 mm/yr (from 1962 to 2001) and 0.6 mm/yr (from 2001 to 2004) is tentatively interpreted as resulting from the current occurrence of a decade-long episode of aseismic slip involving a large part of the fault plane. Occasionally associated with minor seismicity, this aseismic slip event could betray a thickening of the transitional region located below the upper crustal zone of stable sliding. It causes a total fault slip of 5–10 cm in a few tens of years, releasing smoothly all, or a great part of, the strain accumulated during the previous 1–2 ky of fault quiescence.

Rim Slip and Bead Fitment of Tires: Analysis and Design

Abstract A tire slips circumferentially on the rim when subjected to a driving or braking torque greater than the maximum tire-rim frictional torque. The balance of the tire-rim assembly achieved with weight attachment at certain circumferential locations in tire mounting is then lost, and vibration or adverse effects on handling may result when the tire is rolled. Bead fitment refers to the fit between a tire and its rim, and in particular, to whether a gap exists between the two. Rim slip resistance, or the maximum tire-rim frictional torque, is the integral of the product of contact pressure, friction coefficient, and the distance to the wheel center over the entire tire-rim interface. Analytical solutions and finite element analyses were used to study the dependence of the contact pressure distribution on tire design and operating attributes such as mold ring profile, bead bundle construction and diameter, and inflation pressure, etc. The tire-rim contact pressure distribution consists of two parts. The pressure on the ledge and the flange, respectively, comes primarily from tire-rim interference and inflation. Relative contributions of the two to the total rim slip resistance vary with tire types, depending on the magnitudes of ledge interference and inflation pressure. Based on the analyses, general guidelines are established for bead design modification to improve rim slip resistance and mountability, and to reduce the sensitivity to manufacturing variability. An iterative design and analysis procedure is also developed to improve bead fitment.

Cenozoic deformation history of the Qaidam Basin, NW China: Results from cross-section restoration and implications for Qinghai–Tibet Plateau tectonics

The deformation and uplifting history of the Qinghai–Tibet Plateau is a controversial issue, and so far there has been insufficient evidence for interpretation. Investigations of the Cenozoic deformation in the northeastern edge of this plateau may provide some relevant information. In this paper, the Cenozoic deformation history of the Qaidam Basin has been studied based on results from the balanced cross-section restoration of six geological sections. They indicate that: (1) the Qaidam Basin has been undergoing continuous shortening since the beginning of Cenozoic with two relatively fast shortening phases, the first during 42.8–40.5 Ma and the second during 2.8 Ma–present; (2) the shortening rate of the Qaidam Basin reached its maximum value since 2.8 Ma, and approximately 32% of the average total Cenozoic shortening took place in this period; and (3) the shortening of all sections reached approximately 50% of their respective total shortening by Miocene . The Cenozoic deformation history of the Qaidam Basin shows good synchroneity with uplifting history of the Qinghai–Tibet Plateau. It is therefore proposed that the deformation and uplifting in the south and north edges of the Qinghai–Tibet Plateau was almost synchronous, with the Altyn Tagh Fault formed at the beginning of India–Asia collision. Accordingly, it is postulated that since the India–Asia collision at the beginning of Cenozoic, the Indian Plate moved northward continuously with two relatively fast phases, the first during 42.8–40.5 Ma and the second during 2.8 Ma–present. Approximately 50% of the total Cenozoic northward displacement of the Indian Plate, of the total amount of crustal shortening and uplifting of the Qinghai–Tibet Plateau, and of the total Cenozoic strike slip displacement of the Altyn Tagh Fault were probably reached by the early Miocene. Moreover, another 30–40% might have taken place during 2.8 Ma–present. The periods during 42.8–40.5 Ma and during 2.8 Ma–present may also be the two fast phases for crustal shortening and uplifting of the Qinghai–Tibet Plateau and strike slip displacement of the Altyn Tagh Fault.

Slow slip below Port Blair, Andaman, during the great Sumatra‐Andaman earthquake of 26 December 2004

Although several studies suggest that a slow slip followed the seismic slip on the northern half of the 1300‐km long plate interface that ruptured during the great Sumatra‐Andaman earthquake, the onset and duration of the slow slip remain unresolved. In this paper we analyze a tide gauge record at Port Blair, situated about 1000 km north of the epicenter. Our preferred model, which fits the observed data well, consists of a mixed mode of slip: ∼half of the total slip occurring seismically in less than 5 min after the rupture arrival and the rest developing in the next 30 min. A scenario of slow slip on the northern half of the rupture area, that is consistent with seismic data, and GPS data, consists of slip on the time scale of &lt;35 min over some parts of the fault, such as below Port Blair, and &gt; 1 hour over the rest.

Technique for Measuring Side Slip for Individual Alignment Elements

The current footplate type side slip tester measures only the total side slip. Therefore, measurement techniques by which to determine the side slip for each alignment element was examined. Concretely, because the side slip related to the camber angle varies depending on the unit load per travel wheel and the side slip related to the toe angle depends only the direction of the tire and not on the unit load per travel wheel, the side slip for each alignment element can be determined separately.

Late Cenozoic shortening in the west-central Alborz Mountains, northern Iran, by combined conjugate strike-slip and thin-skinned deformation

The west-central Alborz Mountains of northern Iran have deformed in response to the Arabia-Eurasia collision since ca. 12 Ma and have accommodated 53 ± 3 km of shortening by a combination of range-parallel, conjugate strike-slip faulting and range-normal thrusting. By our interpretation, ∼17 km of shortening across the Alborz is accommodated by westward relative motion of a crustal wedge bounded by conjugate dextral and sinistral strike-slip fault systems. The Nusha, Barir, and Tang-e-Galu fault zones strike west-northwest, constrain the north side of the wedge, and, prior to ca. 5 Ma, accumulated a total of ∼25 km of dextral slip. The south side of the wedge is bounded by the active sinistral reverse Mosha and Taleghan faults, which merge northwest of Tehran and have a total slip estimate of 30–35 km. A restored cross section across the range indicates a minimum of 36 ± 2 km of fold-and-thrust–related, range-normal shortening. Combined, wedge motion, thrusting, and folding yield a net shortening of 53 ± 3 km across the range, which is within the error of the shortening estimate predicted by assuming that the present-day shortening rate (5 ± 2 mm/yr) has been constant since ca. 12 Ma (∼60 km of predicted shortening). A second restored cross section farther west, which includes the wedge, gives a total shortening of 15–18 km and a long-term shortening rate of 1.25–1.5 mm/yr (constant shortening rate since ca. 12 Ma). These strong along-strike finite-strain and long-term strain-rate gradients are important for our understanding of how long-term strain rates compare with instantaneous strain rates derived from global positioning system (GPS) data, and should be considered when planning mountain belt–scale GPS surveys. Finally, a 60-km-long right-hand bend in the Mosha-Taleghan fault system has driven the development of a transpressional duplex south of the fault. The southern boundary of the duplex is the active Farahzad–Karaj–North Tehran thrust system. The kinematic development of this strike-slip duplex has implications for seismic hazard assessment in the heavily populated Karaj and Tehran areas.

Structural geology of a classic thrust belt earthquake: the 1999 Chi-Chi earthquake Taiwan ( Mw=7.6)

We document the structural context of the 1999 Chi-Chi earthquake ( M w=7.6) in western Taiwan, which is one of the best-instrumented thrust-belt earthquakes. The main surface break and large slip (3–10 m) is on two segments of the shallow otherwise aseismic bedding-parallel Chelungpu–Sanyi thrust system, which shows nearly classic ramp-flat geometry with shallow detachments (1–6 km) in the Pliocene Chinshui Shale and Mio-Pliocene Kueichulin/Tungkeng Formations. However, rupture is complex, involving at least six faults, including a previously unknown deeper thrust (8–10 km) on which the rupture began. We compare the coseismic displacements with a new 3D map of the Chelungpu–Sanyi system. The displacements are spatially and temporally heterogeneous and well correlated with discrete geometric segments of the 3D shape of the fault system. Geodetic displacement vectors are statistically parallel to the nearest adjacent fault segment and are parallel to large-scale oblique fault corrugations. The displacement magnitudes are heterogeneous at several scales, which requires in the long term other non-Chi-Chi events or significant aseismic deformation. The Chelungpu thrust has a total displacement of ∼14 km but the area of largest Chi-Chi slip (∼10 m) is on a newly propagated North Chelungpu Chinshui detachment (∼0.3 km total slip) which shows abnormally smooth rupture dynamics.

Paleoseismology of deep‐sea faults based on marine surveys of northern Okushiri ridge in the Japan Sea

The eastern margin of the Japan Sea is an incipient convergent margin characterized by distributed active faults and large‐scale earthquakes. To evaluate the earthquake potential of the northern margin, the source area of the 1940 Shakotan–Hanto‐oki earthquake (M7.5) was reexamined, and the earthquake recurrence interval was estimated by combining bathymetric, seismic, and dive survey data with a tsunami simulation. Seismic profiling clarified that five anticlines have formed in and around this source area during the last 1.8 million years. The balanced cross section of one anticline supports that thrust faults extend to the base of the upper brittle crust at about 11 km depth and total slip is about 850 m. Dive surveys identified fresh collapses along the forelimbs of two anticlines. Inversion of observed tsunami waveforms to estimate the slip distribution suggests that these two anticlines were the sources of the 1940 earthquake. The other three anticlines may be seismic gaps. The dive surveys collected debris layers, possible records of paleoearthquakes, in muddy sediments. From the rate of muddy sediment deposition around the anticlines the minimum recurrence interval of earthquakes was estimated to be about 1100 years. From structural modeling the average interval was about 6400 years, assuming that fault slip started 1.8 million years ago and 3 m of slip occurred during each earthquake. Taking into account the above results and the instantaneous plate convergent rate between the Okhotsk and Amurian plates, the recurrence interval was inferred to be 1100 to a few thousand years.