Vertical Slip Rate Research Articles

Quaternary deformation along the Meeman‐Shelby Fault near Memphis, Tennessee, imaged by high‐resolution marine and land seismic reflection profiles

AbstractA series of high‐resolution seismic reflection surveys was carried out in 2008, 2010, and 2011, providing a total of five new seismic profiles constraining the location and character of the Meeman‐Shelby Fault (MSF), about 9 km west of Memphis, Tennessee, in the Central U.S. The MSF is the best documented fault closest to Memphis yet discovered and shows a recurrent fault history. The fault, as imaged by the reflection profiles, is ~45 km long, strikes N25°E, and dips west‐northwest ~83°, exhibiting an up‐to‐the‐west sense of motion with a possible right‐lateral strike‐slip component. The data show that on average, the MSF offsets the Paleozoic unit ~77 m and folds the top of the Cretaceous unit and the Paleocene‐Eocene Wilcox Group ~44 and ~25 m, respectively. One seismic profile acquired along the Mississippi River images the bottom of the Quaternary alluvium warped up ~28 m, indicating recent activity of the MSF. Calculated vertical slip rates of the MSF during the deposition of the Upper Cretaceous, Paleocene, Eocene, and Quaternary sediments are 0.0022, 0.0010, 0.0004, and 0.2154 mm/yr, respectively, suggesting an increase in fault activity during the Quaternary. Consistent with the present stress field and the deformation of the New Madrid seismic zone fault system, we interpret the MSF as a P shear fault in the context of a left‐stepping, right‐lateral constraining strike‐slip fault system under a nearly east‐west oriented compressional stress field. Source scaling estimates indicate that the MSF is capable of generating a M6.9 earthquake if rupturing in one event.

On-land active thrust faults of the Nankai–Suruga subduction zone: The Fujikawa-kako Fault Zone, central Japan

Abstract This paper describes the tectonic topography that characterizes recent thrusting along, the on-land active fault zone of the Nankai–Suruga subduction zone, called the Fujikawa-kako Fault Zone, located near the triple junction of the Eurasian (EUR), Philippine Sea (PHS), and North American (NA) plates, in the western side of Mt. Fuji, central Japan. The analysis was based on interpretations of aerial photographs and 3D perspective images made with Digital Elevation Model (DEM) data, field investigations, and trench excavations. Our study shows the following new observations: 1) distinct east-facing fault scarps are developed on the west-facing slopes, alluvial fans, and terraces of western Mt. Fuji; ii) the total length of the fault zone is ~ 40 km; iii) the Older stage (ca. 8000–14,000 yr) Fuji lavas have been displaced by as much as 70 m; and iv) the 864–865 AD Jogan lava flow is displaced by 2–4 m vertically along the scarp at the northeastern end of the fault zone. Based on the offsets of lavas and mudflow deposits, as well as historical records, it is found that i) the vertical slip rate for the fault zone is up to 5–8 mm/yr, ii) the recurrence interval of morphogenic earthquakes is estimated to be 150–500 yr, and iii) the most recent seismic faulting event along the Fujikawa-kako Fault Zone is inferred to be related to the 1854 AD (M 8.0–8.5) Ansei-Tokai earthquake. When compared with the active intraplate faults of Honshu, Japan, the relatively high slip rates and short recurrence intervals for morphogenic earthquakes in the Fujikawa-kako Fault Zone indicate that the activity of this fault zone is closely related to subduction-zone earthquakes and plate convergence near the triple plate junction of the EUR, PHS, and NA plates.

Late Quaternary slip rate of the South Heli Shan Fault (northern Hexi Corridor, NW China) and its implications for northeastward growth of the Tibetan Plateau

AbstractBased on field investigations, aerial‐photo morphological analysis, topographic profiling, and optically stimulated luminescence (OSL) dating of alluvial surfaces, we estimate vertical components of the slip rate along the South Heli Shan thrust fault, which lies on the northern margin of the Hexi Corridor and the northeastern edge of the Tibetan Plateau. The fault consists of three segments with scarp heights ranging from less than 1 m to more than 16 m. OSL dating indicates that most of the alluvial fans cut by fault scarps formed during the transition from the last glacial stage to the present interglacial stage from ~19 to ~9 ka along southern Heli Shan and from ~27 ka to ~22 ka along its northern margin. In addition, remnants of older alluvial fan have been abandoned after ~67 ka. Scarp heights increase from west to east and reach a maximum of more than 16 m near the eastern end. Using three approaches, we calculate late Quaternary slip rates for each of the three fault segments along the southern margin and the fault on the northern flank. These approaches yield maximum vertical slip rates from 0.18 to 0.2 mm/a for the western segment, 0.3 to 0.43 mm/a for the central segment, 0.36 to 0.53 mm/a for the eastern segment, and 0.21 mm/a for the Wutongjing Fault, which lies on the north side of the Heli Shan. For a range of likely fault dips, these correspond to 0.1–0.2 mm/a of average horizontal shortening for the western segment, and increase to 0.4–0.5 mm/a across the eastern segment of the southern Heli Shan Fault. Combining the height of the eastern parts of the Heli Shan (Daqing Peak) above the Hei He (a major river that incised the western end of the range) and the vertical component of the slip rate of the eastern segment, we suggest that the Heli Shan was uplifted by motion on the South Heli Shan Fault beginning sometime between 1 and 4 Ma, most likely since ~2 Ma. This age suggests that the Tibetan Plateau continues to grow northeastward across the Hexi Corridor.

Differentiating between gravitational and tectonic faults by means of geomorphological mapping, trenching and geophysical surveys. The case of the Zenzano Fault (Iberian Chain, N Spain)

The Zenzano Fault scarp has been developed on the top of a 475m-high erosional escarpment underlain by an upper brittle sequence and a lower halite-bearing evaporitic formation. The 1850m-long fault, with a maximum displacement of 45m and parallel to the escarpment, has offset the back of a dip slope, generating an antislope scarp with prominent triangular facets up to 38m high and obstructing consequent transverse drainages (defeated streams). Both gravitational and tectonic interpretations were previously proposed for this active surface rupture. The fault scarp has been investigated by detailed geological and geomorphological mapping, geophysical surveys (GPR and ERT) and two trenches excavated across the fault in disrupted drainages. The geophysical profiles clearly imaged the fault, helping to site the trenches and roughly estimate the thickness of the deposits accumulated in the downthrown block. Although the maximum displacement to length ratio (Dmax/L) of the fault fall within the range of tectonic faults of similar length, according to the world database, the geological and geomorphological context, together with several parameters reveal that this structure corresponds to a gravitational failure: (1) anomalously high vertical displacement per event (>1.4m); (2) high apparent vertical slip rate (~0.6mm/year); and (3) short recurrence interval of faulting events. The negligible horizontal displacement component on the dip-slip fault, as well as the presence of very large caprock collapse sinkholes and saline springs, strongly suggest that interstratal karstification of the halite-bearing evaporites has played a primary role in the development of the gravitational failure. The formation of this morphostructure has been favoured by pre-existing tectonic faults, erosional unloading related to the removal of an overburden ca. 800m thick, and enhanced groundwater recharge due to the blockage of the drainage. This work illustrates that the proposed multidisciplinary approach allows the identification of features and calculation of parameters that may help to elucidate whether an active failure has a gravitational or a tectonic origin.

Holocene Earthquakes and Late Pleistocene Slip-Rate Estimates on the Wassuk Range Fault Zone, Nevada

The Wassuk Range fault zone is an 80‐km‐long, east‐dipping, high‐angle normal fault that flanks the eastern margin of the Wassuk Range in central Nevada. Observations from two alluvial fan systems truncated by the fault yield information on the vertical slip rate and Holocene earthquake history along the range front. At the apex of the Rose Creek alluvial fan, radiocarbon dating of offset stratigraphy exposed in two fault trenches shows that multiple earthquakes resulted in 7.0 m of vertical offset along the fault since ∼9400 cal B.P. These data yield a Holocene vertical slip rate of 0.7±0.1 mm/yr. The south trench exposure records at least two faulting events since ∼9400 cal B.P., with the most recent displacement postdating ∼2810 cal B.P. The north trench exposure records an ∼1 m offset between ∼610 cal B.P. and A.D. ∼1850, a 1.3‐m minimum offset prior to ∼1460 cal B.P., and one earlier undated earthquake of a similar size. Variations in stratigraphy and limited datable material preclude a unique correlation of paleoevents between the two trenches. Approximately 25 km north, the range‐front fault has truncated and uplifted a remnant of the Penrod Canyon fan by >40 m since the surface was deposited ∼113 ka, based on cosmogenic dating of two large boulders. These data allow an estimate of the minimum late Pleistocene vertical slip rate at >0.3–0.4 mm/yr for the Wassuk Range fault zone. Online Material: Tables summarizing radiocarbon and cosmogenic analyses, photos of rocks sampled for cosmogenic analyses, and figures summarizing cosmogenic exposure age estimates.

Paleoseismic events and recurrence interval along the Beichuan–Yingxiu fault of Longmenshan fault zone, Yingxiu, Sichuan, China

Prior to the 2008 Wenchuan earthquake (Mw 7.9), Sichuan, China, no earthquake of magnitude larger than M 7.0 had been reported in the historical record for the Longmenshan region. To reveal paleoseismic behaviors in this region, we conducted a paleoseismic study along the 2008 Wenchuan earthquake fault scarp at the town of Yingxiu along the Beichuan–Yingxiu fault. Through a trench investigation, geomorphic analysis and radiocarbon dating, we interpret the occurrence of three paleoseismic events (including the Wenchuan earthquake) within the past 6000years. The cumulative vertical displacement resulting from the three seismic events is ~7.6m. The coseismic uplift for the Wenchuan earthquake is ~2.4m. Integrated with previous paleoseismic results along the fault, the age of the penultimate event is constrained between 3300 and 2300cal BP. We suggest the antepenultimate event occurred later than 5920–5730cal BP. An average vertical slip rate of 0.88–0.91mm/year is calculated from the vertical displacement of U2 since 5940–5730cal BP. We estimate that an average recurrence interval of large earthquakes is at most 3000years. Furthermore, the three paleoseismic events revealed at Yingxiu show similar coseismic vertical displacements. We propose that the strain accumulation and deformation across the Longmenshan fault zone is a relatively stable and continuous process since late Quaternary.

Quaternary seismo‐tectonic activity of the Polochic Fault, Guatemala

The Polochic‐Motagua fault system is part of the sinistral transform boundary between the North American and Caribbean plates in Guatemala and the associated seismic activity poses a threat to ∼70% of the country's population. The aim of this study is to constrain the Late Quaternary activity of the Polochic fault by determining the active structure geometry and quantifying recent displacement rates as well as paleo‐seismic events. Slip rates have been estimated from offsets of Quaternary volcanic markers and alluvial fan using in situ cosmogenic 36Cl exposure dating. Holocene left‐lateral slip rate and Mid‐Pleistocene vertical slip rate have been estimated to 4.8 ± 2.3 mm/y and 0.3 ± 0.06 mm/y, respectively, on the central part of the Polochic fault. The horizontal slip rate is within the range of longer‐term geological slip rates and short‐term GPS‐based estimates. In addition, the non‐negligible vertical motion participates in the uplift of the block north of the fault and seems to be a manifestation of the regional, far‐field stress regime. We excavated the first trench for paleo‐seismological study on the Polochic fault in which we distinguish four large paleo‐seismic events since 17 ky during which the Polochic fault ruptured the ground surface.

First indications of high slip rates on active reverse faults NW of Damascus, Syria, from observations of deformed Quaternary sediments: Implications for the partitioning of crustal deformation in the Middle Eastern region

Recent research on rates of crustal shortening within the Palmyra Fold Belt (PFB) in Syria has drawn attention to the possibility that reverse faults near the city of Damascus, which adjoins the SW PFB, have significant slip rates. We infer that the Damascus Fault, directly adjacent to the city, has developed a throw of ~2500m and report the discovery of the en echelon Bassimeh Fault, with a throw of ~1000m, this fault being revealed by warping of the local bedrock and of a terrace, of inferred Late Pleistocene age, of the River Barada. We estimate that this set of faults became active circa 0.9Ma, synchronous with changes to the pattern of faulting previously reported farther southwest in the northern Jordan Valley. Vertical slip rates on the Bassimeh and Damascus faults of ~1.1 and ~2.8mm a−1, respectively, are thus estimated. We also infer that large historical earthquakes, previously attributed to left-lateral faulting farther west on the Dead Sea Fault Zone (DSFZ), probably occurred on this set of reverse faults; these faults thus represent a significant hazard to the city of Damascus. Our observations indicate that as much as half of the northward motion of the Arabian plate, relative to the African plate, may be ‘absorbed’ by crustal shortening within the PFB, potentially explaining the low slip rate recently measured geodetically on the northern DSFZ in western Syria.

Late Holocene episodic displacement on fault scarps related to interstratal dissolution of evaporites (Teruel Neogene Graben, NE Spain)

The Mio-Pliocene formations of the Turolian type section (Teruel Graben, Spain) have sagged due to dissolution of the underlying Triassic evaporites generating a 1.7 km long monocline and accompanying synform with 130 m of structural relief. The crest of the monocline is affected by a graben that counterbalances the shortening caused by passive bending in the adjacent syncline. This graben is controlled by a master synthetic fault and a swarm of antithetic and synthetic faults with a conspicuous geomorphic expression. After acquiring Ground Penetrating Radar (GPR) profiles, three trenches were excavated in depressions associated with uphill-facing fault scarps. To our knowledge, these are the first trenches excavated across faults caused by deep-seated dissolution of evaporites. The geometrical relationships observed in two trenches indicate late Holocene episodic displacement (as many as 3 events). Some of the parameters estimated for the investigated faults are clearly different from those expectable for tectonic faults in this intraplate area. They include high apparent vertical slip rates (0.6–1 mm/yr), low average recurrence of faulting events (1.2–2 ka) and very high displacement per event values (>65 cm) for surface ruptures less then 200 m long. Our findings suggest that considering evaporite collapse faults as creeping structures is not a reliable criterion to differentiate between tectonic faults (seismogenic) and dissolution-induced gravitational faults (nonseismogenic).

Rupture segmentation and slip partitioning of the mid-eastern part of the Kunlun Fault, north Tibetan Plateau

The Kunlun Fault, an active fault on the border between the Bayan Har and Kunlun-Qaidam blocks, is one of the major left lateral strike-slip faults in the Tibetan Plateau. Previous research has not reached a consensus on agreeable slip rates along much of its length and the slip rate gradient along the eastern part, both of which play critical roles in a range of models for the eastward extrusion and thickened crust of the Tibetan Plateau. New slip rates have been determined at sites along the eastern part of the Kunlun Fault by dating deposits and measuring atop displaced fluvial terrace risers. Field investigations and interpretation of satellite images reveal geometrical features of the fault and the late Quaternary offset, new earthquake ruptures and surface-rupturing segmentation, from which long-term slip rates and earthquake recurrence intervals on the fault are estimated. The tectonic geomorphology method has determined that the long-term horizontal slip rates on the Tuosuohu, Maqin and Maqu segments from west to east are 11.2±1, 9.3±2, and 4.9±1.3 mm/a while their vertical slip rates are 1.2±0.2, 0.7±0.1, and 0.3 mm/a in the late Quaternary. Results indicate that the slip rates regularly decrease along the eastern ∼300 km of the fault from >10 to <5 mm/a. This is consistent with the decrease in the gradient such that at the slip rate break point is at the triple point intersection with the transverse fault, which in turn is transformed to the Awancang Fault. The vector decomposition for this tectonic transformation shows that the western and eastern branches of the Awancang Fault fit the slip-partitioning mode. The slip rate of the southwestern wall is 4.6 mm/a relative to the northeastern wall and the slip direction is 112.1°. The mid-eastern part of the Kunlun Fault can be divided into three independent segments by the A’nyemaqen double restraining bend and the Xigongzhou intersection zone, which compose the surface rupture segmentation indicators for themselves as well as the ending point of the 1937 M7.5 Tuosuohu earthquake. The average recurrence interval of the characteristic earthquakes are estimated to be 500–1000 a, respectively. The latest earthquake ruptures occurred in AD 1937 on the western Tuosuohu segment, as compared to ∼514–534 a BP on the Maqin segment, and ∼1055 to 1524 a BP on the Maqu segment. This may indicate a unidirectional migration for surface rupturing earthquakes along the mid-eastern Kunlun Fault related to stress triggered between these segments. Meanwhile, the long-term slip rate is obtained through the single event offset and the recurrence interval, which turn out to be the same results as those determined by the offset tectonic geomorphology method, i.e., the decreasing gradient corresponds to the geometrical bending and the fault’s intersection with the transverse fault. Therefore, the falling slip rate gradient of the mid-eastern Kunlun Fault is mainly caused by eastward extension of the fault and its intersection with the transverse fault.

Pliocene to Quaternary tectonics in the Horná Nitra Depression (Western Carpathians)

Pliocene to Quaternary tectonics in the Horná Nitra Depression (Western Carpathians)The Horná Nitra Depression is an Upper Miocene-Quaternary intramontane sedimentary basin. This N-S elongated half-graben structure is rimmed from the west by the marginal Malá Magura fault which is the most distinctive fault in the Horná Nitra Depression, traditionally considered as an active fault during the neotectonic phase. This dislocation is attended by contrasting landforms and their parameters. The lowS-indexof about 1.10, at least two generations of well-preserved faceted slopes along this fault, and longitudinal river valley profiles point to the presence of a low-destructed actual mountain front line, which is typical for the Quaternary active fault systems. Comparison with known normal fault slip rates in the world makes it possible to set an approximate vertical slip rate between 0.3-1.1 m · kyr-1. The present-day fault activity is considered to be normal, steeply dipping towards the east according to structural and geophysical data. The NNW-SSE present-day tectonic maximum horizontal compressional stressSHand perpendicular minimum horizontal compressional stressShwas estimated in the Horná Nitra region. The Quaternary activity of the Malá Magura fault is characterized by irregular movement. Two stages of important tectonic activity along the fault were distinguished. The first stage was dated to the Early Pleistocene. The second stage of tectonic activity can by dated to the Late Pleistocene and Holocene. The Malá Magura fault is permeable for gases because the soil atmosphere above the ca. 150 meters wide fault zone contains increased contents of methane and radon.

Range-Bounding Normal Fault of Smith Valley, Nevada: Limits on Age of Last Surface-Rupture Earthquake and Late Pleistocene Rate of Displacement

Abstract Smith Valley is bounded on its western edge by an active normal fault and the Pine Nut mountains. Displacement on the fault is responsible for development of one of the westernmost basins of the Basin and Range province of the western United States. Interpretation of an exposure afforded by excavation of a trench across the range-bounding fault places the most recent surface-rupture earthquake after 5176±130 cal yr B.P. and suggests it was close in time to 3530±82 cal yr B.P. Utilization of tephrochonologic and cosmogenic analyses and mapping of fault scarps across the Artesia Road fan are the basis for putting forth an initial estimate of the late Pleistocene vertical slip rate of the fault at between 0.125 mm/yr and 0.33 mm/yr.

Glacis geometry as a geomorphic marker of recent tectonics: The Guadix–Baza basin (South Spain)

The Guadix–Baza basin occupies 4000 km 2, and constitutes the largest intramontane basin of the Betic Cordillera (Southern Spain). It has a well preserved geomorphic surface, a glacis, which started to be eroded when the basin conditions changed from endorheic to exorheic. Taking into account its large preserved surface area (more than 1200 km 2) and its pre-deformational geometry, this geomorphic surface is a useful marker of recent deformation. Combining geological and geomorphological data and high resolution DEM, topographic profiles of the glacis have been produced to estimate vertical displacements caused by active compression and extension structures. These structures have produced relative vertical displacements of up to 100 m from the late middle Pleistocene to the present. Assuming an age for the glacis of between 205 and 600 ka, it has been possible to estimate long-term minimum and maximum vertical rates of the activity of normal faults and folds using this geomorphic surface as a marker. Vertical slip rates range from 0.07 to 0.49 mm/year for the main active normal faults and vertical folding rates range from 0.05 to 0.17 mm/year for several active folds. These long-term vertical slip and folding rates are in accordance with other values previously estimated in other sectors of the Betic Cordillera. When present, detailed geomorphic study of recent glacis is an excellent tool for evaluating active tectonics over large regions.

Ultrashallow seismic imaging of the causative fault of the 1980, M6.9, southern Italy earthquake by pre‐stack depth migration of dense wide‐aperture data

A two‐step imaging procedure, including pre‐stack depth migration (PSDM) and non‐linear multiscale refraction tomography, was applied to dense wide‐aperture data with the aim of imaging the causative fault of the 1980, M6.9, Irpinia normal faulting earthquake in a very complex geologic environment. PSDM is often ineffective for ultrashallow imaging (100 m of depth and less) of laterally heterogeneous media because of the difficulty in estimating a correct velocity model for migration. Dense wide‐aperture profiling allowed us to build accurate velocity models across the fault zone by multiscale tomography and to record wide‐angle reflections from steep reflectors. PSDM provided better imaging with respect to conventional post‐stack depth migration, and improved definition of fault geometry and apparent cumulative displacement. Results indicate that this imaging strategy can be very effective for near‐surface fault detection and characterization. Fault location and geometry are in agreement with paleoseismic data from two nearby trenches. The estimated vertical fault throw is only 29–38 m. This value, combined with the vertical slip rate determined by trench data, suggests a young age (97–127 kyr) of fault inception.

The Capo Vaticano (Calabria) coastal terraces and the 1905 M7 earthquake: the geomorphological signature of regional uplift and coseismic slip in southern Italy

Terra Nova, 22, 378–389, 2010 Abstract The elevation of the Capo Vaticano coastal terraces (Tyrrhenian coast, central Calabria) is the result of a combination of regional uplift and repeated coseismic displacement. We subtract the regional uplift from the total uplift (maximum average uplift rates: 0.81–0.97 mm a−1 since c. 0.7 Ma) and obtain the residual fault-related displacement. Then, we model the residual displacement to provide constraints on the location and geometry of the seismogenic source of the 1905 M7 earthquake, the strongest – and still poorly understood – earthquake of the instrumental era in this area. We try four different potential sources for the dislocation modelling and find that (1) three sources are not compatible with the displacement observed along the terraces and (2) the only source consistent with the local deformation is the 100°-striking Coccorino Fault. We calculate average long-term vertical slip rates of 0.2–0.3 mm a−1 on the Coccorino Fault and estimate an average recurrence time of ∼one millennium for a 1905-type earthquake.

Structural deformation and fault activity of the Tan-Lu Fault zone in the Bohai Sea since the late Pleistocene

The Tan-Lu Fault zone (TLFZ) is a significant fractural zone in eastern China and also a seismicity belt in North China. Based on total 4000-km-long shallow penetrated single seismic data with high-resolution, structural deformation and fault activity of the TLFZ in the Bohai Sea since the late Pleistocene are discussed in detail. The results show that the TLFZ with a discontinuous distribution and a general NNE-trending consists of 14 active subfaults with an NNE or NE strike in the Bohai Sea. Seismic data reveal that deformation zones along the subfaults in the central Bohai Sea and the Laizhou Bay are wider and more complex than those in the Liaodong Gulf. Related folds and lots of secondary normal faults which are characterized by nearly vertical fault planes and a same or reverse dip construct the fractural zone in the Laizhou Bay and the central Bohai Sea. Usually, micro symmetrical grabens develop on the top of anticlines. In the Liaodong Gulf, subfault fractural zones usually consist of secondary normal faults with the same inclination or opposite inclination. Ages of seismic sequences and cutting relation between subfaults and seismic sequences suggest that the latest faulting age of the TLFZ is the end of the late Pleistocene in the Liaodong Gulf and the early Holocene in the Laizhou Bay and the central Bohai Sea. There is a good match between distribution of earthquakes and that of the subfaults in the Laizhou Bay and the central Bohai. Statistical result shows that total vertical offset of the TLFZ since the late Pleistocene ranges from 6 to 11 m. On the basis of offsets of the subfaults, the vertical slip rate is calculated and results show that average vertical slip rates in the central Bohai Sea are larger than those in the Liaodong Gulf and the Laizhou Bay. Slip rates more than 0.06 mm/a during 23-10 ka B.P. and 85-65 ka B.P. are larger than those in other stages. The TLFZ was mainly dominated by tensional normal component since the late Pleistocene. Synthesizing shallow deformation, activity and distribution of earthquakes, the TLFZ in the Bohai Sea can be divided into three segments: the Laizhou-Bay segment, the Bozhong segment, and the Liaodong-Gulf segment.

Growth Normal Faulting at the Western Edge of the Metropolitan Taipei Basin since the Last Glacial Maximum, Northern Taiwan

Growth strata analysis is an useful tool in understanding kinematics and the evolution of active faults as well as the close relationship between sedimentation and tectonics. Here we present the Shanchiao Fault as a case study which is an active normal fault responsible for the formation of the 700-m-thick late Quaternary deposits in Taipei Basin at the northern tip of the Taiwan mountain belt. We compiled a sedimentary record, particularly the depositional facies and their dated ages, at three boreholes (SCF-1, SCF-2 and WK-1, from west to east) along the Wuku Profile that traverses the Shanchiao Fault at its central segment. By incorporating the global sea level change curve, we find that thickness changes of sediments and changes of depositional environments in the Wuku area are in a good agreement with a rapid sea level rise since the Last Glacial Maximum (LGM) of about 23 ka. Combining depositional facies changes and their ages with their thickness, we are able to introduce a simple back-stripping method to reconstruct the evolution of growing strata across the Shanchiao Fault since the LGM. We then estimate the vertical tectonic slip rate since 23 ka, which exhibits 2.2 mm yr-1 between SCF-2 and WK-1 and 1.1 mm yr-1 between SCF-1 and SCF-2. We also obtain the Holocene tectonic subsidence rate of 2.3 mm yr-1 at WK-1 and 0.9 mm yr-1 at SCF-2 since 8.4 ka. We thus conclude that the fault zone consists of a high-angle main fault to the east between SCF-2 and WK-1 and a western lower-angle branch fault between SCF-1 and SCF-2, resembling a tulip structure developed under sinistral transtensional tectonism. We find that a short period of 600-yr time span in 9 8.4 ka shows important tectonic subsidence of 7.4 and 3.3 m for the main and branch fault, respectively, consistent with possible earthquake events proposed by previous studies during that time. A correlation between geomorphology and subsurface geology in the Shanchiao Fault zone shows that an array of subtle geomorphic scarps corresponds to the branch fault, however, that the surface trace of the main fault seems to be completely erased by the surface force of erosion and sedimentation. We recommend that analysis in the light of growth-faulting scheme should be conducted in a more systematic way for earthquake geology study in other portions of the Shanchiao Fault within the Taipei Basin, as well as other areas worldwide currently under extensional deformation.

Paleoseismology of the Yangsan Fault, southeastern part of the Korean Peninsula

The NNE-trending Yangsan Fault (YSF) is the most prominent fault in the southeastern part of the Korean Peninsula and has a continuous trace about 200 km long. Activity on this fault was recently investigated using aerial photographs, topographic analysis, and trenching. The geomorphologic evidence of Late Quaternary faulting is clearly recognized on both the northern (Yugyeri and Tosung-ri areas) and southern parts (Eonyang to Tongdosa area) of the fault. The main YSF is marked by a zone of shattered rock that is tens of meters wide and zone of fault gouge. During the Late Quaternary, right-lateral movement occurred mainly on the southern part, as shown by lowangle striations on the fault plane, elongation of deformation features in the fault gouge. The estimated vertical slip rate is about 0.02-0.07 mm/yr, and the lateral slip rate may be several times larger than the vertical rate. The most recent event occurred prior to deposition of Holocene alluvium. In the northern part, the fault locally changes trend to almost N-S, dips to the east and has reverse movement. The average vertical slip rate is estimated less than 0.1 mm/yr. The most recent event probably occurred after 1314 cal. years BP (A.D. 536).

Paleoseismology of silent faults in the Central Apennines (Italy): the Mt. Vettore and Laga Mts. Faults

Paleoseismological analyses have been performed in the Central Apennines along faults showing geomorphological evidence of Late Quaternary activity and characterised by the absence of historical seismicity. Three trenches were made along the Mt. Vettore Fault, across a scarp on a Late Pleistocene-Holocene alluvial fan. The youngest displacement event (E1) occurred after 4155-3965 years BP and before the 6th-7th century A.D., a previous event (E2) occurred between 5940-5890/5795-5780 years BP and 4155-3965 years BP, while the oldest event (E3) occurred between 18.000-12.000 years BP and 5940-5890/5795-5780 years BP. One trench was excavated across the Laga Mts. Fault which gave evidence for two displacement events after 8320-8150 years BP. The minimum vertical slip rate estimated through the paleoseismological analysis of the Mt. Vettore Fault is 0.11-0.36 mm/yr, while the minimum slip rate along the Laga Mts. Fault is 0.12 mm/yr. The paleoseismologically inferred recurrence interval is not longer than 4690 years for the Mt. Vettore Fault and not longer than 7570 years for the Laga Mts. Fault, while the minimum elapsed times since the last activation are 1300 and 800 years for the two faults, respectively. The evaluation of the former elapsed time was based on paleoseismological data, while the estimation of the latter was based on the absence of historical earthquakes which may have been caused by the Laga Mts. Fault and on the completeness of the historical catalogues for the large magnitude events in the last eight centuries. Based on the length of the fault at the surface, earthquakes with M 6.5 and 6.6 may be expected from the activation of the Mt. Vettore and Laga Mts. faults, respectively.

Paleoseismological data from a new trench across the El Camp Fault(Catalan Coastal Ranges, NE Iberian Peninsula)

The El Camp Fault (Catalan Coastal Ranges, NE Iberian Peninsula) is a slow slipping normal fault whose seismic potential has only recently been recognised. New geomorphic and trench investigations were carried out during a training course across the El Camp Fault at the La Porquerola alluvial fan site. A new trench (trench 8) was dug close to a trench made previously at this site (trench 4). With the aid of two long topographic profiles across the fault scarp we obtained a vertical slip rate ranging between 0.05 and 0.08 mm/yr. At the trench site, two main faults, which can be correlated between trenches 8 and 4, make up the fault zone. Using trench analysis three paleoseismic events were identified, two between 34.000 and 125.000 years BP (events 3 and 2) and another event younger than 13 500 years BP (event 1), which can be correlated, respectively, with events X (50.000125.000 years BP), Y (35.000-50.000 years BP) and Z (3000-25.000 years BP). The last seismic event at the La Porquerola alluvial fan site is described for the first time, but with some uncertainties.