Fault Slip Rates Research Articles

Late Quaternary Fault Activity of the Southern Segment of the Daliangshan Fault along the Southeastern Margin of the Tibetan Plateau and Its Implications for Fault Rupture Behaviour at Stepovers

Abstract Stepovers have been widely suggested to be important structural boundaries that control earthquake rupture extent and therefore the size of earthquakes. Previous studies suggested that ~4-5 km wide stepovers are likely to arrest fault rupture. However, recent earthquake cases show that even much wider stepovers (e.g., ≥7-8 km wide) sometimes may not effectively impede seismic rupture propagation, which requires us to further explore cascading rupture mechanism of large earthquakes at wider stepovers. Here, we constrained slip rates and paleoseismic earthquakes of two fault sections that bound a constraining stepover with width of approximately 7-8 km along the southern segment of the Daliangshan fault along the southeastern margin of the Tibetan Plateau. Multiple landform offset and radiocarbon dating results constrained that the two fault sections show a moderate slip rate at approximately 5 mm/yr. Moreover, three or four paleoseismic events Z through W, in 1489 AD, 620-515 BC, 4475-3700 BC, and 6265-4510 BC, were revealed on the Jiaojihe fault section. Based on the aforementioned results, we suggest that the most recent seismic event might exhibit a jump over the restraining stepover, whereas ruptures of the older events might be arrested by the stepover. Furthermore, we suggest that moderate slip-rate faults might have similar potential with that of high slip-rate faults to rupture through wider stepovers, which increases us in understanding the generation of cascading ruptures on strike-slip faults and is helpful for evaluating seismic hazards.

Late Quaternary Slip Rates for the Hyde and Dunstan Faults, Southern New Zealand: Implications for Strain Migration in a Slowly Deforming Continental Plate Margin

AbstractReverse faulting in Otago, southern New Zealand, accommodates distributed tectonic convergence on the eastern side of the Australian‐Pacific plate boundary. Paleoearthquake records from some of the faults in the region show highly variable earthquake recurrence times, with long periods of quiescence separated by periods of earthquake activity. Here we develop a longer‐term context for these records, using cosmogenic radionuclide dating of faulted alluvial fan surfaces to characterize the late Quaternary slip rates on two significant faults within the system, the Hyde and Dunstan faults. We determine an average slip rate of 0.24 mm/yr (0.19–0.29 mm/yr at 95% confidence) for the Hyde Fault since about 115 ka, and an average slip rate of 0.16 mm/yr (0.12–0.21 mm/yr) for the Dunstan Fault since about 320 ka. Both faults show increases in slip rate of a factor of three to five times the average long‐term rate over timescales of 10 kyr. Increases in slip rate are out of phase on the two faults, supporting a hypothesis that strain is shared within the fault system over timescales on the order of 10 kyr. Over longer timescales, on the order of 100 kyr, slip rates can be well‐approximated by a linear fit, providing an upper limit on the variability of fault slip rates with time.

GPS Determined Asymmetric Deformation Across Central Altyn Tagh Fault Reveals Rheological Structure of Northern Tibet

AbstractWe establish a continuous GPS transect crossing the central Altyn Tagh fault at 90°E with eight years of observations. GPS velocities along this profile and another one crossing the fault at 86°E suggest a fault slip rate of 12.4 ± 0.7 mm/yr, but with asymmetric straining of adjacent terrain. On the south side, ∼8.2 mm/yr of left‐lateral shear is absorbed across a region ∼210 km from the fault, but only ∼4.2 mm/yr is found on the north side. This estimate of slip rate is ∼30% larger than the consensus estimate of previous models. By treating the deforming regions as elastic plates with different thicknesses overlying a substrata that obeys a linear Maxwell viscoelastic constitutive relationship, we infer a viscosity of ∼5.1 × 1019 Pa s (between 3.5 and 9.1 × 1019 Pa s at 1‐σ) on the south side, beneath northern Tibetan Plateau. This low viscosity, compared to some estimates for the asthenosphere, concurs with the Tibetan Plateau being underlain by a relatively hot and weak lower crust and upper mantle. The effective elastic thickness on the south side is 16.5–20 km, which is significantly smaller than that of the Tarim Basin of >60 km.

Seismicity of the repeating earthquake clusters in the northern Xiaojiang fault zone and its implications

The Xiaojiang fault zone (XJF), located at the southeastern margin of the Tibetan plateau, has been frequently struck by destructive earthquakes throughout history. Some studies showed that repeating earthquakes may be used to estimate fault slip rates and even to monitor the pre-slip prior to large asperity. This study focuses on the repeating earthquakes recorded by a high-density seismic array in the northern section of the XJF, a segment ruptured by the 1733 Dongchuan M7.8 earthquake. Using the waveform cross-correlation and relocation techniques, we processed the continuous seismic recordings from seismic stations of the array and confirmed 27 clusters of repeating earthquakes. The repeaters are located in three relatively independent sub-areas, areas A, B, and C. Area A is close to the source areas of the 2014 Ludian Ms6.5 and the 2020 Qiaojia Ms5.0 earthquakes; by analyzing the recurrence intervals of repeating clusters, we found that the Ludian earthquake had an insignificant triggering effect on surrounding events, while the triggering effect from the Qiaojia earthquake was obvious. The clusters in area B were located very close to the northernmost tip of the XJF, which should be associated with an asperity preparing for a large earthquake on the northern XJF. Together with a repeating cluster identified in a previous study and the seismicity pattern revealed by our seismic array, we determined the geometry of the asperity and slip rate, which further helps to estimate a potential Mw7.1 earthquake for the asperity, where no M>7 earthquakes have occurred since the 1733 Dongchuan M7.8 earthquake. The clusters in area C are more like human-induced earthquakes because they are concentrated during the daytime when local people are at work, and, thus, they cannot be used for the study of tectonic deformation. This study clearly indicates that the repeating earthquakes can be triggered by a moderate earthquake nearby and also that repeating earthquakes can be used to estimate fault slip rates and outline locked asperities.

A Dense Block Model Representing Western Continental United States Deformation for the 2023 Update to the National Seismic Hazard Model

Abstract Seismic hazard assessment, such as the U.S. Geological Survey (USGS) National Seismic Hazard Model (NSHM), relies on estimates of fault slip rate based on geology and/or geodetic observations such as the Global Navigation Satellite System (GNSS), including the Global Positioning System. Geodetic fault slip rates may be estimated within a 3D spherical block model, in which the crust is divided into microplates bounded by mapped faults; fault slip rates are determined by the relative rotations of adjacent microplates. Uncertainty in selecting appropriate block-bounding faults and in forming closed microplates has limited the interpretability of block models for seismic hazard modeling. By introducing an automated block closure algorithm and regularizing the resulting densely spaced block model with total variation regularization, I develop the densest and most complete block model of the western continental United States to date. The model includes 853 blocks bounded by 1017 geologically identified fault sections from the USGS NSHM Fault Sections database. Microplate rotations and fault slip rates are constrained by 4979 GNSS velocities and 1243 geologic slip rates. I identify a regularized solution that fits the GNSS velocity field with a root mean square misfit of 1.9 mm/yr and reproduces 57% of geologic slip rates within reported geologic uncertainty and model sensitivity, consistent with other geodetic-based models in this Focus Section. This block model includes slip on faults that are not included in the USGS NSHM Fault sections database (but are required to form closed blocks) for an estimate of “off-fault” deformation of 3.62×1019 N·m/yr, 56% of the total calculated moment accumulation rate in the model.

Numerical simulation of contemporary kinematics at the northeastern Tibetan Plateau and its implications for seismic hazard assessment

Abstract. The slip rates of active faults in the northeastern Tibetan Plateau (NETP) require clarification to understand the lateral expansion of the Tibetan Plateau and assess the seismic hazards in this region. To obtain the continuous slip rates of active faults at the NETP, we constructed a three-dimensional (3D) numerical geomechanics model that includes a complex 3D fault system. The model also accounts for the physical rock properties, gravity fields, fault friction coefficients, initial stress, and boundary conditions. Following this, we present the long-term kinematics of NETP based on the horizontal and vertical velocities and fault slip rates acquired from the model. The fault kinematic characteristics indicate that the Laohushan, middle–southern Liupanshan, and Guguan–Baoji faults, as well as the junction area of the Maxianshan and Zhuanglanghe faults, are potential hazard areas for strong earthquakes. However, as these faults are currently in the stress accumulation stage, they are unlikely to cause a strong earthquake in the short term. In contrast, it is likely that the Jinqiangshan–Maomaoshan fault will generate a earthquake with a surface-wave magnitude (MS) of 7.1–7.3 in the coming decades. In addition, the velocity profiles across the NETP imply that the plate rotation is the primary deformation mechanism of the NETP even though the intra-block straining and faulting are non-negligible.

Estimating the long-term slip rate of active normal faults: The case of the Paganica Fault (Central Apennines, Italy)

The footwall of the surface rupturing Paganica normal fault, the source of the 2009 L’Aquila earthquake (Mw 6.1) in the Central Apennines (Italy), was investigated using integrated geological and geomorphological approaches. The aim was to constrain the active tectonics by studying the Raiale River that orthogonally crosscuts the fault trace, where it provides a useful geomorphological marker of long-term fluvial incision and footwall uplift. Using morphostratigraphy and paleomagnetic analysis, the Plio–Pleistocene morphotectonic evolution of the area was reconstructed, comprising an ancient continental basin and paleolandforms that predate the footwall incision. Starting from the Late Early Pleistocene–Middle Pleistocene, fluvial dissection was mainly due to marked river downcutting triggered by significant activity of the Paganica Fault, which caused progressive base-level lowering. The Raiale River downcutting formed five Middle–Late Pleistocene fluvial terraces, that, along with absolute Optically Stimulated Luminescence (OSL) dating, allowed the identification of paleolongitudinal profiles with a diverging downstream configuration. Terrace dating yielded a minimum incision rate of 0.25 ± 0.02 mm/a, which only partially compensates the footwall uplift and can thus be considered as a minimum value for the Paganica Fault throw rate, which could reach up to ~0.45 mm/a. In parallel, using terrestrial cosmogenic nuclides, a denudation rate of 0.02–0.04 mm/a was measured on the summit of the footwall block. This denudation is in keeping with the drainage incision, suggesting a non-steady state for the fault footwall topography and a dominance of relief growth. Last, the analysis of the modern Raiale River longitudinal profile denoted an ungraded status, with two main knickzones that we interpret as transient forms due to tectonic perturbations, likely triggered by activity of the Paganica Fault during the end Early Pleistocene and the Late Pleistocene. Considering the 2009 L’Aquila earthquake coseismic rupture, we observe that the younger transience on the Raiale River longitudinal profile, if it is of tectonic origin, could have only been produced by much larger seismic events (i.e., Mw > 6.5) than those documented in the area by paleoseismological investigations. The collective results confirmed that in the Central Apennines, conditions of dynamic equilibrium are often not met, and that the persistence of transient perturbations induced by tectonics should be accounted for.

Fault locking of the Qilian–Haiyuan fault zone before the 2022 Menyuan Ms6.9 earthquake and its seismic hazards in the future

By using GPS-derived velocities of 2015–2021 and a negative dislocation program, we inverted the locking degree and slip rate deficit in the Qilian–Haiyuan fault zone, and combined with the distribution of small earthquakes in the fault, we studied the characteristics before the 2022 Menyuan MS6.9 earthquake and analyzed the future seismic hazards of each segment within this fault zone. The regional crustal deformation pattern is discussed with regard to the fault slip rate and regional strain rate field. The preliminary results show that before the earthquake, the seismogenic fault was strong locked, with a high locking depth, the slip rate deficit was large, and the distribution of small earthquakes was relatively few, these characteristics are closely related to the occurrence of strong earthquakes, according to the aftershock relocation results, further, it is believed that the earthquake may link the Lenglongling and Tuolaishan faults into a large strike-slip fault. The Jinqianghe fault, the Lenglongling fault, and the eastern segment of the Tuolaishan fault are strongly locked, with high locking depth and large slip rate deficit, combined with the occurrence of small earthquakes and the locking degree before the 2022 Menyuan MS6.9 earthquake, indicate that the eastern segment of the Tuolaishan fault is highly likely to have strong earthquakes in the future, which requires further attention. In addition, the strike-slip rate of the Qilian–Haiyuan fault zone is mainly between 3.9 and 4.3 mm/yr, the overall movement of the fault is consistent, and the compressional rate gradually decreases from 2.9 mm/yr in the western segment to 1 mm/yr in the eastern segment; the fault compressional rate may be related to the crustal shortening (formation basin and uplift mountain). Therefore, the present-day crustal deformation in the northeastern margin of the Tibetan Plateau is mainly distributed in the shortened region of the crust on the Qilian Shan area and left-lateral strike-slip localized on the Qilian–Haiyuan fault zone.

Crustal Strain Rates in the Western United States and Their Relationship with Earthquake Rates

Abstract We present a suite of strain rate models for the western United States based on geologic and geodetic data. The geologic data consist of Quaternary fault-slip rates and the geodetic data consists of a new compilation of Global Positioning System (GPS) velocities derived from continuous, semicontinuous, and campaign measurements. We remove postseismic deformation from the GPS time series in order for our geodetic strain rate model to best capture the interseismic strain accumulation rate. We present models based on either geologic or geodetic data, but also create a hybrid model. Although there are some differences between the models, the large-scale features are the same, with the noticeable exception for the Pacific Northwest where interseismic strain is naturally more distributed than the long-term strain release. We also present a map of earthquake rate densities based on mainshocks, and the result has similar spatial features similar to the strain rate models (at least in the southwestern United States). We perform a general correlation analysis between strain rate and seismicity rate (south of Cascadia) and find a change in linearity between seismicity and strain rates from slow to faster deforming areas with seismicity rates relatively lower for the latter. The extent of that change depends a bit on assumptions made on the declustering and completeness of the catalog, but the finding of a change in slope is robust across the different strain rate models. Linearity for all areas is only expected when Gutenberg–Richter parameters and parameters involved in the conversion from strain to moment rate are uniform across the study area. We discuss these qualifications, but find no single satisfactory explanation for our observation. Moreover, when considering a rather short time and space, theoretical considerations of sampling from a power-law distribution actually predict there to be a power law instead of a linear relationship, generally consistent with our observation.

Active crustal deformation model of the Fen–Wei rift zone, North China: Integration of geologic, geodetic, and stress direction datasets

The Fen–Wei rift zone (FWRZ) of North China is an important zone of active crustal deformation representing a transition from extrusion tectonics related to the Tibetan Plateau to subduction tectonics related to the potential far-field influence of the west Pacific plate. In this study, we determined the kinematic constraints of active crustal deformation in the FWRZ, which are fundamental for forecasting seismicity. NeoKinema, a kinematic finite-element model, was employed to estimate the long-term fault slip rates, distributed crustal deformation field, and on- and off-fault strain-rate fields in the FWRZ by fitting updated geological fault slip rate, geodetic GPS velocity, and principal compressive stress direction datasets. Our results show that the FWRZ is a characteristic low-strain kinematic setting, with most active faults exhibiting slip rates of less than 1 mm/a. The total sinistral shear rate from the southern Ordos block to the Qinling Mountains is approximately 1 mm/a, indicating limited tectonic extrusion along the EW-trending Qinling Mountains. Additionally, the central Shanxi rift exhibits prominent dextral shear of ∼0.5 mm/a that decreases toward its north and south ends, corresponding to crustal extension of 1.1–1.2 mm/a in the Datong and Yuncheng basins, respectively. However, this significant crustal extension cannot be solely attributed to terminal effects caused by dextral shear in the central Shanxi rift. A comparison between predicted seismicity and historical earthquake records reveals some remarkable seismic gaps, particularly in the Datong, Hancheng, and Yuncheng basins, indicating higher seismic potential in these locations. This study provides insights into the long-term crustal deformation processes and regional seismic potential of the FWRZ.

Climate-driven stress changes and normal fault behavior in the Lake Malawi (Nyasa) Rift, East Africa

Climate-triggered fluctuations of surface masses, including ice and water, can cause transient stress in the Earth's crust, further affecting the slip behavior of faults over different temporal and length scales. In particular, lakes developed within active continental rifts may modulate the stress states and slip rates of rift border faults and intrarift faults. Here, we utilize a numerical model in a case study of the Malawi (Nyasa) Rift to understand the response of faults to mass fluctuations on the Earth's surface. The water level of Lake Malawi rose 600 m over the last 150 kyr, and significantly influenced the stress state of faults in rift valley. We find that such water load fluctuations can exert 4.6 MPa normal stress on fault planes and produce a negative Coulomb stress (down to −2.0 MPa) on fault planes as well as a pronounced reduction of slip (∼2 m) on fault planes within the rift. Moreover, along-strike differences in fault geometries and their position relative to the center of the water column load resulted in variable along-strike stress and slip changes. These results suggest that lakes that develop within continental rifts play an important role in the evolution of extensional faulting. Our case study provides a basis for evaluating the relationship between climate-driven surface mass variations and the subsurface stress state of fault planes and associated seismic potentials.

Constraining Paleoseismicity of the Wulashan Piedmont Fault on the Northern Margin of the Ordos Block From Fault Scarp Morphology

Fault scarps preserve important information about past earthquakes on a fault, and thus can be applied to investigate the fault slip histories and rupture patterns. In this study, the morphology of fault scarps was used to constrain the paleoseismicity of the Wulashan Piedmont Fault located on the northern margin of the Ordos Block based on high-resolution LiDAR topography. We constructed the vertical displacement distribution of the fault through measuring the heights of a large number of scarp profiles extracted on different geomorphic surfaces along the fault. Through statistical analysis of the dense collection of vertical displacement dataset, a total of seven paleoseismic events were identified which followed a characteristic slip pattern with an average slip of ∼1.0 m. We further detected slope breaks in the fault scarp morphology to quantify the number of paleoearthquakes that occurred on the scarps, and discriminated at least five individual surface-breaking events. Both the number and slip of paleoearthquakes recognized from the morphology of fault scarps were in good agreement with previous paleoseismic trenching records. Based on the empirical scaling relationship between moment magnitude and rupture parameters, a moment magnitude ofMw6.7–7.5 was determined for the paleoearthquakes occurred on the fault. With the fault slip rate derived by previous studies, we estimated an average recurrence interval of 1.3–1.8 kyr for the paleoseismic events, which is very close to the elapsed time since the most recent earthquake, indicating a high potential seismic hazard on the Wulashan Piedmont Fault.

The cryptic seismic potential of the Pichilemu blind fault in Chile revealed by off-fault geomorphology

The first step towards assessing hazards in seismically active regions involves mapping capable faults and estimating their recurrence times. While the mapping of active faults is commonly based on distinct geologic and geomorphic features evident at the surface, mapping blind seismogenic faults is complicated by the absence of on-fault diagnostic features. Here we investigated the Pichilemu Fault in coastal Chile, unknown until it generated a Mw 7.0 earthquake in 2010. The lack of evident surface faulting suggests activity along a partly-hidden blind fault. We used off-fault deformed marine terraces to estimate a fault-slip rate of 0.52 ± 0.04 m/ka, which, when integrated with satellite geodesy suggests a 2.12 ± 0.2 ka recurrence time for Mw~7.0 normal-faulting earthquakes. We propose that extension in the Pichilemu region is associated with stress changes during megathrust earthquakes and accommodated by sporadic slip during upper-plate earthquakes, which has implications for assessing the seismic potential of cryptic faults along convergent margins and elsewhere.

Late Quaternary slip rate of the northern Lancangjiang fault zone in eastern Tibet: Seismic hazards for the Sichuan-Tibet Railway and regional tectonic implications

The Sichuan-Tibet Railway in eastern Tibet runs across numerous seismogenic faults with high seismic risks. The Lancangjiang fault (LCJF), one of the essential strike-slip faults within the Qiangtang block, traverses the railway. However, the geometry and late Quaternary activities of the LCJF remain unclear, limiting the assessment of seismic hazards on the Sichuan-Tibet Railway and the understanding of kinematic patterns in eastern Tibet. Based on the interpretation of high-resolution satellite imagery, field observations, and shallow geophysical exploration, we first mapped the detailed geometry of the northern LCJF. It consists of two branches: Yangda-Yaxu fault (YYF) and Baqing-Leiwuqi fault (BLF), which merge eastwards onto the main LCJF. Displaced landforms and multiple numerical dating techniques reveal that the YYF is a mainly sinistral fault with a late Quaternary slip rate of ~2.2 + 0.6/−0.5 mm/yr and a minor vertical component (~0.1 mm/yr). The BLF undergoes an oblique motion with a left-lateral slip rate of ~1.2 + 0.5/−0.3 mm/yr and a northeast-vergent reverse rate of ~1.2 + 0.4/−0.2 mm/yr in the Holocene. Vector analysis of slip rates suggests that the LCJF has a sinistral rate of ~3.5 + 1.1/−0.8 mm/yr with a reverse component of ~1.6 + 0.4/−0.3 mm/yr, displaying an essential role in strain partitioning of eastern Tibet. Together with slip rates of other intra-block faults, the kinematic pattern of eastern Tibet probably applies to the sub-block model. Offset geologic units yield a total displacement of ~10–11 km for the YYF. Using the slip rate of the YYF, the LCJF was initiated at ~5.9–3.9 Ma, probably related to the establishment of the present-day strain pattern and the onset of crustal thickening in eastern Tibet during the late Miocene. In addition, the active YYF and BLF across the Sichuan-Tibet Railway have a seismic potential of Mw ~7.2–7.3 that will produce a ~ 1.8–2.0 m sinistral slip on the YYF, and a ~ 2.0 m horizontal, and ~ 1.1–1.3 m reverse motion on the BLF. They will pose a high seismic hazard potential on the railway. This study provides quantitative data for regional seismic hazard analysis and shows insights into the deformation mechanism of the plateau.

Activity Analysis of the Fuyu North Fault, China: Evidence from the Time-Series InSAR, GNSS, Seismic Reflection Profile, and Plate Dynamics

Abstract Earthquake disasters are frequent, and the seismic intensity is large in Northeast China. Earthquake activity research is an important aspect of earthquake disaster management. We chose some unconventional means to study fault activity, to find updated activity evidence. The Ms 5.3 earthquake occurred near the Fuyu North Fault (FNF) of China on May 27, 2018. Using the Sentinel-1B descending orbit data from 2016 to 2019, the line-of-sight (LOS) surface deformation in the study area was calculated by using the small baseline subset (SBAS) method. After transforming to the horizontal EW deformation, the variance component estimation method was used for fusion reconstruction with the EW data of the surrounding GNSS stations. The polynomial least square method is used to fit the fault slip rate of three EW data on the surface trace of the FNF. The fitting results of the three regions show that the horizontal eastward distribution rate of the upper plate is significantly greater than that of the lower plate, which is left-lateral clockwise torsion. The vertical structural deformation caused by the growth strata of the upper and lower plates of the upper SYT2 seismic profile of the FNF is quantitatively calculated, and the thrust rate of the upper plate is 0.2 mm/y relative to that of the lower plate. Based on the Li Siguang chessboard structure model, we found that the compression stress in the north-south direction is gradually weakened, and the compression stress in the east-west direction is gradually enhanced. Through the Coulomb stress analysis, the three events of CMT only induced the historical focal location of the surrounding part. The events of 2017 did not induce the events of 2018, but the events of 2019 were related to the induced effects of 2017 and 2018.

Late Pleistocene Slip Rates on an Active Normal Fault in the Northwestern Ordos Block, China

The slip rates of normal faults on the northern margin of the Ordos Block are critical for understanding the deformation of the Ordos Block and adjacent areas. In this study, we obtain the late Pleistocene slip rate of an active normal fault, the Zhuozishan West Piedmont Fault (ZWPF), in the northwestern corner of the Ordos Block. Satellite imagery interpretation and field investigations suggest that the fault displaces late Pleistocene alluvial fans and forms west-facing fault scarps. To quantify the vertical slip rate of the ZWPF, we measured the displacements along the fault scarps using differential GPS and an unmanned aerial vehicle system and dated the displaced geomorphic surfaces using optically stimulated luminescence (OSL) dating methods. The vertical slip rate of the fault is constrained to 0.1 ± 0.02 mm/a, which suggests a horizontal extension rate of 0.05 mm/a for a dip of 65°. This rate is consistent with those on similar structures in the northwestern Ordos Block. Combining this result with published slip rates along other active faults, we infer that the NW-directed extension rate across the northwestern corner of the Ordos Block is ∼0.6–1.3 mm/a. This rate is comparable with the geodetic strain rate. Given the extension rate, we believe that extensional deformation is mainly concentrated on the western side of the basin.

The High-Frequency Signature of Slow and Fast Laboratory Earthquakes.

Tectonic faults fail through a spectrum of slip modes, ranging from slow aseismic creep to rapid slip during earthquakes. Understanding the seismic radiation emitted during these slip modes is key for advancing earthquake science and earthquake hazard assessment. In this work, we use laboratory friction experiments instrumented with ultrasonic sensors to document the seismic radiation properties of slow and fast laboratory earthquakes. Stick‐slip experiments were conducted at a constant loading rate of 8 μm/s and the normal stress was systematically increased from 7 to 15 MPa. We produced a full spectrum of slip modes by modulating the loading stiffness in tandem with the fault zone normal stress. Acoustic emission data were recorded continuously at 5 MHz. We demonstrate that the full continuum of slip modes radiate measurable high‐frequency energy between 100 and 500 kHz, including the slowest events that have peak fault slip rates <100 μm/s. The peak amplitude of the high‐frequency time‐domain signals scales systematically with fault slip velocity. Stable sliding experiments further support the connection between fault slip rate and high‐frequency radiation. Experiments demonstrate that the origin of the high‐frequency energy is fundamentally linked to changes in fault slip rate, shear strain, and breaking of contact junctions within the fault gouge. Our results suggest that having measurements close to the fault zone may be key for documenting seismic radiation properties and fully understanding the connection between different slip modes.

36Cl exposure dating of glacial features to constrain the slip rate along the Mt. Vettore Fault (Central Apennines, Italy)

The Central Apennines are among the most seismically active regions in Italy. This region is affected by an extension accommodated by active normal faults. Those faults with high seismogenic potential hosted Mw > 6 shallow damaging earthquakes, such as the Mw 6.5 event of Oct. 30, 2016. Although fault slip rates are crucial to seismic hazard assessments, in the Central Apennines, slip rate assessments encompassing several seismic cycles (> 10 ka) are sparse. This is particularly true for the Mt. Vettore-Mt. Bove Fault system that ruptured during the mainshocks of the 2016–2017 seismic sequence. In this study, we present new geochronological constraints of offset geomorphological markers along the northern portion of the fault system on the Mt. Porche Fault segment using in-situ produced 36Cl cosmogenic nuclides. Offset measurements were made using a 5-cm resolution DEM obtained through a drone survey and constrained a fault scarp height of 15.5 ± 1.4 m and a maximal cumulative offset estimated between 32 and 40.5 m. Samples were collected from the Valle Lunga terminal moraine at 1710 m asl and yielded 36Cl exposure ages of 12.7 + 2.2/−1.9 ka, while the abraded surface, located on top of the tectonic scarp yielded 36Cl exposure ages of 23.4 + 5.3/−4.3 ka. Using the fault scarp height and the exposure age of this abraded surface, we constrained a minimum vertical fault slip rate of 0.7 + 0.2/−0.1 mm/yr. Assuming the offset started to accumulate when climate conditions allowed the scarp preservation, we constrained a maximal vertical slip rate of 1.2 ± 0.2 mm/yr along the main fault of the Mt. Vettore-Mt. Bove Fault system. This rate is higher than those previously obtained from trenches along secondary branches of the Mt. Vettore-Mt. Bove Fault system. Besides, the yielded chronology for the last glacial maximum in that area at ~23 ka is in good agreement with the timing previously proposed for the LGM in the Apennines.

Asymmetric Interseismic Strain across the Western Altyn Tagh Fault from InSAR

As the northern boundary of the Tibetan Plateau, the long Altyn Tagh fault (ATF) controls the regional tectonic environment, and the study of its long-term fault slip rate is key to understanding the tectonic evolution and deformation of the northern Tibetan Plateau. In this paper, we measure the fault slip rate of the western segment of the ATF using InSAR observations between 2015 to 2020. The Multi-Temporal Interferometric InSAR analysis is applied to obtain the two-dimensional fault-parallel and vertical displacement fields. The spatially dense InSAR observations clearly illustrate the asymmetrical pattern of displacement fields across the fault. Constrained by our InSAR observations, the fault slip rate and locking depth of the western segment of the ATF are inverted using four different models in a Bayesian framework. The two-layer viscoelastic model incorporating lateral heterogeneity of rheology in the lower crust indicates that the fault slip rate of the western ATF is estimated to be 9.8 ± 1.1 mm/yr (at 83.8°E across the ATF) and 8.6 ± 1.1 mm/yr (at 85.1°E), respectively, and the locking depth is 15.8 ± 4.3 km and 14.8 ± 4.9 km. Our new estimates generally agree with the previous estimates of fault slip rate constrained by GPS observations. We conclude that the contrast between the thickness of the elastic layer and the shear modulus of the Tibetan plateau and the Tarim basin jointly contribute to the asymmetric interseismic strain accumulation on the ATF.

Tectonic geomorphology of active faults in Eastern Crete (Greece) with slip rates and earthquake history from cosmogenic 36Cl dating of the Lastros and Orno faults

In eastern Crete, several normal faults trend both NNE-SSW and E-W. Most of them form impressive bedrock fault scarps indicating ongoing extension in the Hellenic fore-arc. No earthquakes from historical and instrumental catalogues can be directly associated with these faults. Geomorphologic profiles across five different faults in sites well-preserved from erosion, deposition or human intervention revealed displacements of ∼6.9 m–∼30 m. Following a robust site selection at the Lastros and Orno faults, we mapped different categories of weathered horizontal ribbons along the bedrock fault plane based on colour contrast, lichen colonisation and karstic features that affect fault plane roughness, features that altogether are interpreted as earthquake horizons. The data indicate coseismic displacements of 15–35 cm for the last three earthquakes at the Lastros fault and 10–20 cm for the last two earthquakes at the Orno fault. To constrain the age of these earthquakes and to estimate millennial fault slip rates, we determined cosmogenic 36Cl concentrations from vertical profiles composed of 24 samples from the exposed Lastros fault plane and 7 samples of the Orno fault plane. Bayesian Markov Chain Monte Carlo (MCMC) modelling implies that the last three earthquakes at the Lastros fault, occurred within the last 1.8 ± 1.2 kyr (EQ1 = 1.1 ± 1.1 kyr, EQ2 = 1.4 ± 1.1 kyr, EQ3 = 1.8 ± 1.2 kyr). Furthermore, Lastros’ slip rate varied with a rate of 0.6 ± 0.3 mm/yr during the last 1.8 ± 1.2 kyr, preceded by a rate of 1.1 ± 0.4 mm/yr from ∼1.8 to 8 kyr; suggesting periods of earthquake clustering. At the Orno fault, the last two earthquakes occurred within the last ∼3.5 kyr accompanied with a slip rate of 0.16+0.06-0.02 mm/yr during postglacial times. This confirms for the first time based on absolute dating, that both NNE-SSW and E-W trending neighbouring faults in Crete were active during the Holocene.Most of the 13.2 m high Orno fault scarp was exhumed during glacial times, with an apparent slip rate of 0.28+0.12-0.07 mm/yr. The upper part of the Lastros fault scarp (9–12 m) and the apparent age of the four Lastros footwall samples (∼17.9 kyr, ∼26.0 kyr, ∼29.9 kyr, ∼37.4 kyr) underline the long preservation throughout glacial times as well. These findings show that the general hypothesis of predominantly postglacial bedrock fault scarps needs to be regarded with caution at lower latitudes and/or low altitudes (<1000 m), since degradation processes are weaker.