A new geological slip rate estimate for the Calico Fault,eastern California: implications for geodetic versus geologic rate estimates in the Eastern California Shear Zone

ABSTRACT

Accurate estimation of fault slip rate is fundamental to seismic hazard assessment. Previous work suggested a discrepancy between short-term geodetic and long-term geologic slip rates in the Mojave Desert section of the Eastern California Shear Zone (ECSZ). Understanding the origin of this discrepancy can improve understanding of earthquake hazard and fault evolution. We measured offsets in alluvial fans along the Calico Fault near Newberry Springs, California, and used several techniques to date the offset landforms and determine a slip rate. Our preferred slip rate estimate is 3.2 ± 0.4 mm/yr, representing an average over the last few hundred thousand years, faster than previous estimates. Seismic hazard associated with this fault may therefore be higher than previously assumed. We discuss possible biases in the various slip rate estimates and discuss possible reasons for the rate discrepancy. We suggest that the ECSZ discrepancy is an artefact of limited data, and represents a combination of faster slip on the Calico Fault, off-fault deformation, unmapped fault strands, and uncertainties in the geologic rates that have been underestimated. Assuming our new rate estimate is correct and a fair amount (40%) of off-fault deformation occurs on major ECSZ faults, the summed geologic rate estimate across the Mojave section of the ECSZ is 10.5 ± 3.1 mm/yr, which is equivalent within uncertainties to the geodetic rate estimate.     

Coexisting tectonic settings: the example of the southern Tyrrhenian Sea

We performed geodetic strain rate analyses in southern Italy, using new GPS velocities. Two-dimensional strain and rotation rate fields were estimated and results show that most of the shortening is distributed in the northern Sicily offshore. Extension becomes more evident and comparable with shortening on the eastern side of the same margin, and greater in the eastern Sicily offshore. Principal shortening and extension rate axes are consistent with long-term geological features: seismic reflection profiles show both active compressive and extensional faults affecting Pleistocene strata. We show evidence for contemporaneous extension and transtension in the Cefalù Basin. Combining geodetic data and geological features point to the coexistence of independent geodynamic processes, i.e., the active E–W backarc spreading in the hangingwall of the Apennines subduction zone and shortening along the southern margin of the Tyrrhenian backarc basin operated by the NNW-motion of Africa relative to Eurasia.     

Recent crustal deformation and seismicity studies at Abu-Dabbab area, Red Sea, Egypt

The Abu-Dabbab area is characterized by high seismicity and complex tectonic setting; for these facts, a local geodetic network consisting of 11 geodetic benchmarks has been established. The crustal deformation data in this area are collected using the GPS techniques. Five campaigns of GPS measurements have been collected, processed, and adjusted to get the more accurate positions of the GPS stations. The horizontal velocity vectors, the dilatational, the maximum shear strains, and the principal strain rates were estimated. The horizontal velocity varies in average between 3 and 6 mm per year across the network. The results of the deformation analysis indicate a significant contraction and extension across the southern central part of the study area which is characterized by high seismic activity represented by the clustering shape of the microearthquakes that trending ENE. The north and northeastern parts are characterized by small strain rates. This study is an attempt to provide valuable information about the present state of the crustal deformation and its relationship to seismic activity and tectonic setting at the Abu-Dabbab area. The present study is the first work demonstrating crustal deformation monitoring at the Abu-Dabbab area. The time interval is relatively short. Actually, these results are preliminary results. So, the continuity of GPS measurements is needed for providing more information about the recent crustal deformation in that area.     

Active crustal deformation in two seismogenic zones of the Pannonian region — GPS versus seismological observations

The seismicity and the associated seismic hazard in the central part of the Pannonian region is moderate, however the vulnerability is high, as three capital cities are located near the most active seismic zones. In our analysis two seismically active areas, the Central Pannonian and Mur-Mürz zones, have been considered in order to assess the style and rate of crustal deformation using Global Positioning System (GPS) and earthquake data.We processed data of continuous and campaign GPS measurements obtained during the years 1991–2007. Velocities relative to the stable Eurasia have been computed at HGRN, CEGRN and EPN GPS sites in and around the Pannonian basin. Uniform strain rates and relative displacements were calculated for the investigated regions. GPS data confirm the mostly left lateral strike slip character of the Mur-Mürz–Vienna basin fault system and suggest a contraction between the eastward moving Alpine-North Pannonian unit and the Carpathians.The computation of the seismic strain rate was based on the Kostrov summation. The averaged unit norm seismic moment tensor, which describes the characteristic style of deformation, has been obtained from the available focal mechanism solutions, whereas the annual seismic moment release showing the rate of the deformation was estimated using the catalogues of historical and recent earthquakes.Our analysis reveals that in the Central Pannonian zone the geodetic strain rate is significantly larger than the seismic strain rate. Based on the weakness of the lithosphere, the stress magnitudes and the regional features of seismicity, we suggest that the low value of the seismic/geodetic strain rate ratio can be attributed to the aseismic release of the prevailing compressive stress and not to an overdue major earthquake. In the Mur-Mürz zone, although the uncertainty of the seismic/geodetic strain rate ratio is high, the seismic part of the deformation seems to be notably larger than in the case of the Central Pannonian zone. These results reflect the different deformation mechanism, rheology and tectonic style of the investigated zones.     

Recent and active tectonics of the external zone of the Northern Apennines (Italy)

We present a comprehensive study of the recent and active tectonics of the external part of the Northern Apennines (Italy) by using morphotectonic, geological–structural, and stratigraphic analysis, compared with the current seismicity of the region. This analysis suggests that the external part of the Northern Apennines is characterised by presence of three major systems of Quaternary compressive structures corresponding to (1) the Apenninic watershed, (2) the Apennines–Po Plain margin (pede-Apenninic thrust front), and (3) the Emilia, Ferrara, and Adriatic Fold systems buried below the Po Plain. Geological data and interpreted seismic sections indicate a roughly N–S Quaternary deformation direction, with rates <2.5 mm/year. The shortening decreased since the Pliocene, when our data indicate compression in a NNW–SSE direction and rates up to 7 mm/year. The trend and kinematics of the structures affecting the Apennines–Po Plain margin and the Po Plain subsoil fit well the pattern of the current seismicity of the area, as well as recent GPS and geodetic levelling data, pointing to a current activity of these thrust systems controlled by an overall compressive stress field. Close to the Apenninic watershed, earthquake focal mechanisms indicate that shallow extension is associated to deep compression. The extensional events may be related to a secondary extensional stress field developing on the hangingwall of the thrust system affecting the Apenninic watershed; alternatively, this thrust system may have been recently deactivated and overprinted by active normal faulting. Deeper compressive events are related to the activity of both a major basement thrust that connects at surface with the pede-Apenninic thrust front and a major Moho structure.     

Short-term vertical velocity field in the Apennines (Italy) revealed by geodetic levelling data

We estimate current vertical movements along the Apennines (Italy) through repeatedly measured high precision levelling routes. In order to highlight regional crustal deformation the analysis of a geodetic database, with a minimum benchmark density of 0.7 bm/km (1943–2003 time period), is carried out. We evaluate systematic and random error and their propagation along the levelling routes. Tests on original raw height data have been carried out to define error propagation. The computed relative vertical rates stand significantly above error propagation. A series of traverses along and across the Apennines and a map of relative vertical velocities reveal a geodetic signal characterised by values up to 2.5–3.0 mm/a and by wavelengths up to 100 km.     

Recent terrestrial and satellite observations to model deformations at Colli Albani volcano (central Italy)

The Colli Albani volcanic complex (Rome, Italy) has been dominated by episodic eruptions commencing around 561?ka and ending with the most recent activity of the Albano maar phase (<70?ka). Earthquakes of moderate intensity, gas emissions and significant ground deformations are the recent evidences of a residual activity. Former geodetic data from leveling surveys, GPS stations and InSAR observations tracked ongoing significant uplift of the order of few mm/year near the Colli Albani western flank. Different uplift rates were detected by each technique in different time spans, suggesting also the possibility of sporadic recharge of the hydrothermal system. The renewed high precision leveling data from IGMI survey carried out in 1997/1999 and the last leveling survey carried out in 2006 show that the uplift along the route is currently significant at an average rate of ~3?mm/year. Radar interferograms from ALOS satellite show uplift rate of ~6?mm/year, southwest of the central sector of the leveling route. We have undertaken a joint inversion of the various geodetic data (vertical rates from leveling surveys, GPS site velocities and InSAR observations acquired by ALOS satellite) using a nonlinear inversion technique to estimate the parameters of a point-pressure source, possibly capable of explaining the ongoing deformation at Colli Albani volcano.     

Co-seismic displacements associated to the Molise (Southern Italy) earthquake sequence of October–November 2002 inferred from GPS measurements

The 2002 earthquake sequence of October 31 and November 1 (main shocks Mw = 5.7) struck an area of the Molise region in Southern Italy. In this paper we analyzed the co-seismic deformation related to the Molise seismic sequence, inferred from GPS data collected before and after the earthquake, that ruptured a rather deep portion of crust releasing a moderate amount of seismic energy with no surface rupture. The GPS data have been reduced using two different processing strategies and softwares (Bernese and GIPSY) to have an increased control over the result accuracy, since the expected surface displacements induced by the Molise earthquake are in the order of the GPS reliability. The surface deformations obtained from the two approaches are statistically equivalent and show a displacement field consistent with the expected deformation mechanism and with no rupture at the surface. In order to relate this observation with the seismic source, an elastic modeling of fault dislocation rupture has been performed using seismological parameters as constraints to the model input and comparing calculated surface displacements with the observed ones. The sum of the seismic moments (8.9 × 10¹⁷ Nm) of the two main events have been used as a constraint for the size and amount of slip on the model fault while its geometry has been constrained using the focal mechanisms and aftershocks locations. Since the two main shocks exhibit the same fault parameters (strike of the plane, dip and co-seismic slip), we modelled a single square fault, size of 15 km × 15 km, assumed to accommodate the whole rupture of both events of the seismic sequence. A vertical E–W trending fault (strike = 266°) has been modeled, with a horizontal slip of 120 mm. Sensitivity tests have been performed to infer the slip distribution at depth. The comparison between GPS observations and displacement vectors predicted by the dislocation model is consistent with a source fault placed between 5 and 20 km of depth with a constant pure right-lateral strike-slip in agreement with fault slip distribution analyses using seismological information. The GPS strain field obtained doesn't require a geodetic moment release larger than the one inferred from the seismological information ruling out significant post-seismic deformation or geodetic deformation released at frequencies not detectable by seismic instruments. The Molise sequence has a critical seismotectonic significance because it occurred in an area where no historical seismicity or seismogenic faults are reported. The focal location of the sequence and the strike-slip kinematics of main shocks allow to distinguish it from the shallower and extensional seismicity of the southern Apennines being more likely related to the decoupling of the southern Adriatic block from the northern one.     

Co‐seismic deformation and post‐glacial slip rate along the Magallanes‐Fagnano fault,Tierra Del Fuego,Argentina

Across the extreme south of Patagonia, the Magallanes‐Fagnano Fault (MFF) accommodates the left‐lateral relative motion between South America and Scotia plates. In this paper, we present an updated view of the geometry of the eastern portion of the MFF outcropping in Tierra del Fuego. We subdivide the MFF in eight segments on the basis of their deformation styles, using field mapping and interpretation of high‐resolution imagery. We quantify coseismic ruptures of the strongest recorded 1949, M_w7.5 earthquake, and determine its eastern termination. We recognize several co‐seismic offsets in man‐made features showing a sinistral shift up to 6.5 m, greater than previously estimated. Using ¹⁰Be cosmogenic nuclides depth profiles, we date a cumulated offset in post‐glacial morphologies and estimate the long‐term slip rate of the eastern MFF. We quantify a 6.4 ± 0.9 mm/a left‐lateral fault slip rate, which overlaps geodetic velocity and suggests stable fault behaviour since Pleistocene.     

Active tectonics in the Assam seismic gap between the meizoseismal zone of AD 1934 and 1950 earthquakes along eastern Himalayan front,India

The Assam Seismic Gap has witnessed a long seismic quiescence since the \({ Mw}{\sim }8.4\) great Assam earthquake of AD 1950. Owing to its improper connectivity over the last decades, this segment of the Himalaya has long remained inadequately explored by geoscientists. Recent geodetic measurements in the eastern Himalaya using GPS document a discrepancy between the geologic and geodetic convergence rates. West to east increase in convergence rate added with shorter time span earthquakes like the 1697 Sadiya, 1714 (\({ Mw}{\sim }8\)) Bhutan and 1950 (\({ Mw}{\sim } 8.4\)) Tibet–Assam, makes this discrepancy more composite and crucial in terms of seismic hazard assessment. To understand the scenario of palaeoearthquake surface rupturing and deformation of youngest landforms between the meizoseismal areas of \({ Mw}{\sim }8.1\) 1934 and 1950 earthquakes, the area between the Manas and Dhanshiri Rivers along the Himalayan Frontal Thrust (HFT) was traversed. The general deformation pattern reflects north-dipping thrust faults. However, back facing scarps were also observed in conjugation to the discontinuous scarps along the frontal thrust. Preliminary mapping along with the published literature suggests that, in the eastern Himalayan front the deformation is taking place largely by the thrust sheet translation without producing a prominent fault-related folds, unlike that of the central and western Himalayas.     

Contributions to the Deformation Analysis in Germany Based on Precise and Continuous GPS Measurements

Modern space geodetic techniques enable deformation monitoring of continental plate interiors with high spatial and temporal coverage. Resolving data and results are currently evaluated for their application for the integrated assessment of seismic hazard and risk in Germany. This goes especially for regions where earthquakes are generally rare but high magnitudes are still not unrealistic while vulnerability of today’s society is steadily growing. The present contribution deals with the continuous monitoring of tectonic fracture systems in Germany using the GPS. The estimation of the station velocities with GPS and the resulting geodetic strain is supposed to provide additional input to the earthquake hazard assessment. Unfortunately, the low expected and currently seen velocities (<1–2 mm/year) make it extremely difficult to distinguish between noise and a tectonic signal. Because of the short observation interval the velocity uncertainties are about 2 mm/year in the horizontal components. The essential goal of this program is to provide and model highly precise deformation data and to discuss its needs for a better assessment of geological hazard, especially for the most active tectonic regions in Germany, the Rhine-Graben, the Swabian Alb, the Alpine foreland, and the Vogtland. Here we present preliminary results from 2 years of measurements at currently 150 GPS stations throughout Germany. The time span of this program has proven to be too short and the density of the station network to be not dense enough yet for reliable significant horizontal station velocities and supporting the earthquake hazard assessment.     

祁连山北缘—河西走廊地区大地形变与地震的关系

河西走廊—祁连山北缘地区地处青藏高原北缘,受印度板块与欧亚板块中生代末—新生代早期的碰撞及持续至今的向北推挤作用的远程效应的影响,该地区是现今的地壳活动地区,其中地壳形变是最主要的表现形式。地壳形变监测显示,隆起区垂直位移速率最大可达15mm/a,沉降区最大位移速率为-15mm/a。祁连山和河西走廊的相对隆升变化与该区地震具有密切的关系,河西走廊相对下降、祁连山相对隆升的后期是地震多发时期,河西走廊相对隆升、祁连山相对下降的后期是地震少发时期,这与该区处于挤压体制下的区域构造背景密切相关。GPS水平位移监测显示,河西走廊—祁连山北缘地区全区都一致向东位移,且位移速率非常大,大者大于10mm/a;位移速率具有南部大于北部、东部大于西部的特点,水平位移速率变化与现代活动断裂具有非常密切的关系,并以主要断裂构造为区带的边界;水平位移速率矢量与2002年玉门地震的震源机制解所显示的沿地震破裂面发生的滑动方向非常一致。     

巽他弧北部掸邦高原地壳变形、长期块体运动和发震过程:来自大地测量研究结果的约束

本文通过约束大地测量研究来探索掸邦高原及其周围地区现今的地壳变形和长期块体运动,以期提供该地区地球动力学和相关地震危险状况的最新状态。掸邦高原在横向上由西侧的萨干(Sagaing)断裂和东侧的红河断裂这两条主要断裂包围。其中,青藏高原地壳的韧性流挤压被认为是该夹层变形单元变形的主要因素。大地测量清楚地表明,萨干断裂和红河断裂段分别具有约18 mm/a和约45 mm/a右旋运动走滑速率。此外,掸邦高原内部断层体系大地滑移累积表现为1213 mm/a的整体左旋运动速率。我们认为相对于刚性巽他古陆,研究区域的形变分布和长期块体运动主要受区域书架型断层作用控制,其原因是掸邦高原两侧的主断裂(萨干断裂和红河断裂)存在差异性断裂活动。     

Neotectonic activity and parity in movements of Udaipur block of the Arvalli Craton and Indian Plate

We report site motion of a permanent GPS site at Udaipur (udai), Rajasthan on the Udaipur block of Aravalli Craton. The GPS measurements of 2007–2011 suggest that the site moves at a rate of about 49 mm/year towards northeast. As the site motion is consistent with the predicted plate motion using the estimated euler pole of rotation for the Indian Plate, it implies that there is insignificant internal deformation/strain in the region. Such a deformation is consistent with very low seismic activity in the region. The epicenters of the infrequent low magnitude earthquakes are located on the Precambrian lineaments on the west of Udaipur Block, and on the NW–SE striking younger lineament in the south of the block.     

Microstrain stability of Peninsular India 1864–1994

We report the results of the South Indian Strain Measuring Experiment (SISME) designed to determine whether strain related to microseismicity in the past century may have deformed the networks of the 19th century Great Trigonometrical Survey of India (GTS). More than a dozen GTS points were measured between Mangalore, Madras, and Kanyakumari in southernmost India using GPS geodesy to determine regional deformation. Detailed measurements were made near two of the original baselines of the survey to determine the reliability of dilatational strain data for the network. The regional measurements revealed negligible regional dilatational (+ 11.2 + 10 microstrain) and shear strain changes (0.66± 1.2μradians) in the southernmost 530 km of India. In addition to these measurements, we determined the rate of northward and eastward motion of a point in Bangalore (1991–1994) in the ITRF92 reference frame to be 39 ± 3.5 mm/year, and 51 ± 11 mm/year respectively. This is consistent with NUVEL-1A plate motion estimate for India. Simultaneous measurements to a point near Kathmandu reveal that the Indian plate and the Southern Himalaya are moving approximately in unison, placing an upper limit on the rate of creep processes beneath the lesser Himalaya of ≈6 mm/year, and suggesting relatively rigid behavior of the Indian plate north of Bangalore. The stability of the Indian plate is confirmed by the absence of significant changes in the lengths of the two baselines at Bangalore and Cape Comorin, which, within the limits of experimental error have not changed since 1869. The measurements place an upper limit for recent deformation in the southern peninsula, and hence a lower limit for the renewal time for intraplate earthquakes in the region of approximately 10,000 years, assuming shear failure strain of approximately 100 μradians. This, in turn, implies that recurrence intervals for Peninsular Earthquakes far exceed the length of the written historic record, suggesting that the characterisation of seismic recurrence intervals from historical studies is likely to be fruitless. In contrast, the SISME experiment demonstrates that the noise level of geodetic studies based on 19th century GTS data is less than 0.02 μstrain/year, providing considerable scope for delineating regions of anomalously high seismogenic strain, by GPS measurements at all available trig points of the 19th century GTS survey.     

海原断裂带库仑应力积累

用中国地壳运动观测网络区域站在海原断裂带附近的所有观测数据及跨断裂GPS剖面观测数据作为约束, 用Smith3D体力模型反演了海原断裂带断层滑动速率和断层闭锁深度, 计算了库仑应力积累率和地震矩积累率.采用遗传算法拟合GPS水平运动速度场, 拟合的最后残差均方根为1.2mm/a.反演结果为: 第一段毛毛山断裂左旋走滑运动速率为3.6mm/a, 闭锁深度为22km; 第二段老虎山断裂左旋走滑速率为10.5mm/a, 闭锁深度为11.4km; 第三、四、五段(海原断裂带西段、中段和东段) 滑动速率依次为3.5mm/a、5.8mm/a、5.7mm/a, 闭锁深度依次为8.5km、3.6km、4.3km.海原断裂带库仑应力积累率为0.48~1.59MPa/100a, 毛毛山断裂地震矩积累率较大, 但库仑应力积累率较小; 老虎山断裂库仑应力积累率和地震矩积累率均比较大; 海原断裂带(狭义) 中西段库仑应力积累率最大.      

Seismic potential of Southern Italy

To improve estimates of the long-term average seismic potential of the slowly straining South Central Mediterranean plate boundary zone, we integrate constraints on tectonic style and deformation rates from geodetic and geologic data with the traditional constraints from seismicity catalogs. We express seismic potential (long-term average earthquake recurrence rates as a function of magnitude) in the form of truncated Gutenberg–Richter distributions for seven seismotectonic source zones. Seismic coupling seems to be large or even complete in most zones. An exception is the southern Tyrrhenian thrust zone, where most of the African–European convergence is accommodated. Here aseismic deformation is estimated to range from at least 25% along the western part to almost 100% aseismic slip around the Aeolian Islands. Even so, seismic potential of this zone has previously been significantly underestimated, due to the low levels of recorded past seismicity. By contrast, the series of 19 M6–7 earthquakes that hit Calabria in the 18th and 19th century released tectonic strain rates accumulated over time spans up to several times the catalog duration, and seismic potential is revised downward. The southern Tyrrhenian thrust zone and the extensional Calabrian faults, as well as the northeastern Sicilian transtensional zone between them (which includes the Messina Straits, where a destructive M7 event occurred in 1908), all have a similar seismic potential with minimum recurrence times of M ≥ 6.5 of 150–220 years. This potential is lower than that of the Southern Apennines (M ≥ 6.5 recurring every 60 to 140 years), but higher than that of southeastern Sicily (minimum M ≥ 6.5 recurrence times of 400 years). The high seismicity levels recorded in southeastern Sicily indicate some clustering and are most compatible with a tectonic scenario where the Ionian deforms internally, and motions at the Calabrian Trench are small. The estimated seismic potential for the Calabrian Trench and Central and Western Sicily are the lowest (minimum M ≥ 6.5 recurrence times of 550–800 years). Most zones are probably capable of generating earthquakes up to magnitudes 7–7.5, with the exception of Central and Western Sicily where maximum events sizes most likely do not exceed 7.     

The structure of the upper crust in the Alps-Apennines boundary region deduced from refraction seismic data

Analysis of data gathered during the 1983 European Geotraverse southern segment (EGT-S '83) experiments in the region extending from the Emilia-Liguria Apennines to the western Alpine Arc together with data from seismic profiles in the northwestern Apennines accumulated within the framework of the Alps-Apennines Orogene Study Group indicate new details on the structure of the upper crust east and west of the Alps-Apennines boundary.The main results of this analysis centre on two areas. In the Piedmont Tertiary Basin we could determine the depocenter configurations of the 6–7 km thick terrigenous sequence and differentiate the tectonic units in the Piedmont (Alpine) and the Ligurian (Apennine) domains within the basement. In the other area, the Insubric domain underneath the Ligurian nappes of the northern Apennines, we found indications of tectonic doubling within the terrigenous-carbonate sequence in which thrusting attenuates towards the underlying basement, detected at a depth of 12–15 km. In addition, we found that, on a line from the Emilia Apennines to the Monferrato Hills, displacement of the Ligurian nappes over the Insubric domain diminishes to nearly one-third its original extent.     

Late Quaternary deformation and slip rates in the northern San Andreas fault zone at Olema Valley, Marin County, California

Quaternary sedimentary deposits along the structural depression of the San Andreas fault (SAF) zone north of San Francisco in Marin County provide an excellent record of rates and styles of neotectonic deformation in a location near where the greatest amount of horizontal offset was measured after the great 1906 San Francisco earthquake. A high-resolution gravity survey in the Olema Valley was used to determine the depth to bedrock and the thickness of sediment fill along and across the SAF valley. In the gravity profile across the SAF zone, Quaternary deposits are offset across the 1906 fault trace and truncated by the Western and Eastern Boundary faults, whose youthful activity was previously unknown. The gravity profile parallel to the fault valley shows a basement surface that slopes northward toward an area of present-day subsidence near the head of Tomales Bay. Surface and subsurface investigations of the late Pleistocene Olema Creek Formation (Qoc) indicate that this area of subsidence was located further south during deposition of the Qoc and that it has migrated northward since then. Localized subsidence has been replaced by localized contraction that has produced folding and uplift of the Qoc. This apparent alternation between transtension and transpression may be the result of a northward-diverging fault geometry of fault strands that includes the valley-bounding faults as well as the 1906 SAF trace. The Vedanta marsh is a smaller example of localized subsidence in the fault zone, between the 1906 SAF trace and the Western Boundary fault. Analyses of Holocene marsh sediments in cores and a paleoseismic trench indicate thickening, and probably tilting, toward the 1906 trace, consistent with coseismic deformation observed at the site following the 1906 earthquake.New age data and offset sedimentary and geomorphic features were used to calculate four late Quaternary slip rate estimates for the SAF at this latitude. Luminescence dates of 112–186 ka for the middle part of the Olema Creek Formation (Qoc), the oldest Quaternary deposit in this part of the valley, suggest a late Pleistocene slip rate of 17–35 mm/year, which replaces the unit to a position adjacent to its sediment source area. A younger alluvial fan deposit (Qqf; basal age 30 ka) is exposed in a quarry along the medial ridge of the fault valley. This fan deposit has been truncated on its western side by dextral SAF movement, and west-side-down vertical movement that has created the Vedanta marsh. Paleocurrent measurements, clast compositions, sediment facies distributions, and soil characteristics show that the Bear Valley Creek drainage, now located northwest of the site, supplied sediment to the fan, which is now being eroded. Restoration of the drainage to its previous location provides an estimated slip rate of 25 mm/year. Furthermore, the Bear Valley Creek drainage probably created a water gap located north of the Qqf deposit during the last glacial maximum 18 ka. The amount of offset between the drainage and the water gap yields an average slip rate of 21–30 mm/year. Finally, displacement of a 1000-year-old debris lobe approximately 20 m from its hillside hollow along the medial ridge indicates a minimum late Holocene slip rate of 21–25 mm/year. Similarity of the late Pleistocene rates to the Holocene slip rate, and to previous rates obtained in paleoseismic trenches in the area, indicates that the rates may not have changed over the past 30 ka, and perhaps the past 200–400 ka. Stratigraphic and structural observations also indicate that valley-bounding faults were active in the late Pleistocene and suggest the need for further study to evaluate their continued seismic potential.