Coseismic Displacements Research Articles

Performance of real-time undifferenced precise positioning assisted by remote IGS multi-GNSS stations

The heavy reliance of real-time precise point positioning (RTPPP) on external satellite clock products may lead to discontinuity or even failure in time-critical applications. We present an alternative approach of real-time undifferenced precise positioning (RUP) that, by combining satellite clock estimation and precise point positioning based on the extended Kalman filter, is independent of external satellite clock corrections. The approach is evaluated in simulated real time with the assistance of a variable number of IGS multi-GNSS stations located between 1359.7 and 4852.5 km from the users. The results show that even with a single auxiliary IGS station, RUP is still feasible and able to retain centimeter-level positioning accuracy. Typically, with three auxiliary IGS stations about 2000–3000 km away, an accuracy of about 2 cm in the horizontal and 5 cm in the vertical can be achieved. The performance of RUP is comparable to that of PPP using 5-s satellite clock products and notably exhibits superior short-term precision in dealing with high-rate (1 Hz) GPS/GLONASS observations. The addition of GLONASS observations reduces the convergence time by 56.9% and improves the 3-D position accuracy by 31.8% while increasing the processing latency by a factor of about 1.6. Employing three IGS stations over 2400 km away from the epicenter, RUP is applied for the rapid determination of coseismic displacements and waveforms for the 2016 Kaikoura earthquake, yielding highly consistent results compared to those obtained from post-processed PPP in the global reference frame. We also explore its potential in facilitating real-time online services in terms of real-time precise positioning, zenith tropospheric delay retrieving, and satellite clock estimation.

Seismotectonics of the 2017–2018 Songyuan Earthquake Sequence, Northeastern China: Passive Bookshelf Faulting and Block Rotation in the Songliao Basin

AbstractThe high frequency of earthquake clusters generated by pure strike-slip faulting over the past 3 yr (beginning in 2017 in the Songliao basin, northeastern China) has motivated us to consider why lateral strike slip and not extension determines the seismic activity within the Songliao basin. Precise location and characterization of relocated aftershocks, forward modeling of the coseismic displacement field, and Global Positioning System (GPS) monitoring data are combined to detect the possible seismogenic structures of the Songyuan earthquake sequence. The 2017 ML 5.3 aftershock cluster coincided with the northeast-striking Fuyu–Zhaodong fault (FZF), and the 2018 aftershock swarm followed the linear trend (N42°W) of the Songhuajiang fault (SHF). In addition, the forward modeling results indicate that during the earthquakes, right-lateral and left-lateral strike-slip displacements occurred simultaneously along the FZF and SHF, respectively. These two strike-slip faults joined to accommodate the intervening crustal blocks’ asymmetrical east–west convergence and a single northward extrusion. We also utilize 5 yr of GPS data to construct the regional strain-rate map for the basin. The measurements show that right-lateral transform motion along the immense northeast-striking right-lateral strike-slip faults, for example, the Tanlu fault zone and the FZF, impose a northeast-striking simple shear across the Songliao basin. This simple shear not only caused left-lateral movement on the minor northwest-striking left-lateral strike-slip faults such as the SHF but also rotated them ∼14° clockwise into their present orientations. The results of the proposed bookshelf faulting model in which the predominant northeast-striking parallel faults are initiated are consistent with the observed lineament orientations, focal mechanisms, and earthquake distributions. The sharp shift in the subduction direction of the Pacific plate seems to have had a considerable influence on the intracontinental deformation in China, at least throughout northeastern China.

The November 2019 Seismic Sequence in Albania: Geodetic Constraints and Fault Interaction

The seismic sequence of November 2019 in Albania culminating with the Mw = 6.4 event of 26 November 2019 was examined from the geodetic (InSAR and GNSS), structural, and historical viewpoints, with some ideas on possible areas of greater hazard. We present accurate estimates of the coseismic displacements using permanent GNSS stations active before and after the sequence, as well as SAR interferograms with Sentinel-1 in ascending and descending mode. When compared with the displacements predicted by a dislocation model on an elastic half space using the moment tensor information of a reverse fault mechanism, the InSAR and GNSS data fit at the mm level provided the hypocentral depth is set to 8 ± 2 km. Next, we examined the elastic stress generated by the Mw = 7.2 Montenegro earthquake of 1979, with the Albania 2019 event as receiver fault, to conclude that the Coulomb stress transfer, at least for the elastic component, was too small to have influenced the 2019 Albania event. A somewhat different picture emerges from the combined elastic deformation resulting after the two (1979 and 2019) events: we investigated the fault geometries where the Coulomb stress is maximized and concluded that the geometry with highest induced Coulomb stress, of the order of ca. 2–3 bar (0.2–0.3 MPa), is that of a vertical, dextral strike slip fault, striking SW to NE. This optimal receiver fault is located between the faults activated in 1979 and 2019, and very closely resembles the Lezhe fault, which marks the transition between the Dinarides and the Albanides.

Dominant Afterslip of the 2010 Mw 6.9 Yushu, Tibetan Plateau Earthquake as Derived from GPS Observations: Implication for Seismic Hazard Assessment

The Mw 6.9 Yushu earthquake occurred on 14 April 2010, rupturing the Yushu segment of the previously mapped left-lateral strike-slip Ganzi-Yushu fault, southeastern Tibet. We constructed eight temporary GPS benchmarks across the faulting belt in a quick mode within 1 week after the mainshock. The newly constructed benchmarks and seven pre-existing ones were observed in campaign mode, with each session lasting for 3 consecutive days. The entire observations spanned a period of 250 days until the end of 2010, capturing early post-seismic transients induced by the Yushu earthquake. The GPS-derived post-seismic motions generally had the same orientations as the coseismic displacements. The post-seismic displacement time series are modeled with a logarithmic function, obtaining a characteristic decay time scale of 6.7 ± 0.2 days. Using the GPS site displacements, we investigated the possible mechanism of the stress relaxation process. The estimated surface displacements due to possible poroelastic rebound did not agree with the observed displacements. Multiple tests with various viscoelastic models, including the Burgers model, standard linear solid rheology and Maxwell relaxation model, show that the viscoelastic deformation in the early post-seismic phase was possibly insignificant. Thus afterslip was deemed dominant in the process of stress relaxation. We identified that the afterslip was primarily located at the northwestern and southeastern flanks of coseismic slip distribution, anti-correlated with the coseismic slip spatially. Moreover, we found that the time-dependent afterslip decays rapidly with time. With moments released by the aftershocks and afterslip taken into account, we derived a new recurrence period of 124–452 years for an M 7 class earthquake similar to the Yushu earthquake in the Ganzi-Yushu fault. The newly derived recurrence interval benefits the seismic hazard assessment in the southeastern Tibetan Plateau.

Precise coseismic displacements from the GPS variometric approach using different precise products: Application to the 2008 MW 7.9 Wenchuan earthquake

The Global Positioning System (GPS) variometric approach has emerged as an attractive alternative to traditional well-developed positioning techniques including relative positioning and precise point positioning. Previous studies have demonstrated the capability of the variometric approach to retrieve coseismic displacements at centimeter-level precision, in a real-time manner using only readily available broadcast ephemeris. This study presents the first results comparing the performance of the variometric approach by using a variety of precise satellite orbit and clock products. Totally six kinds of products are included in our evaluation, namely the broadcast, IGS (International GNSS Service) ultra-rapid (predicted), ultra-rapid (observed), rapid, final (30-s clock) and CODE (Center for Orbit Determination in Europe) final (5-s clock) products. Static and dynamic experiments are conducted using 1-Hz GPS data covering a relatively large area in China during the 2008 Wenchuan MW 7.9 earthquake. After removing the linear trend, the displacements using broadcast, ultra-rapid (predicted), ultra-rapid (observed) and rapid products reach nearly equivalent precisions at centimeter level. By using final and CODE final products, the precision of displacements can be significantly improved from 1.9–2.0 cm to 0.4–0.7 cm horizontally, and from 6.0–6.2 cm to 1.0–1.7 cm vertically for the dynamic experiments. The displacements using the CODE final products achieve the best precision, improved by more than 40% compared to those using the IGS final products. With the availability of IGS high-rate real-time precise products, this approach is promising to capture coseismic displacements more precisely in real time, which is crucial for earthquake and tsunami early warning.

Co- and Early Postseismic Deformation Due to the 2019 Ridgecrest Earthquake Sequence Constrained by Sentinel-1 and COSMO-SkyMed SAR Data

Abstract The 2019 Ridgecrest earthquake sequence ruptured a series of conjugate faults in the broad eastern California shear zone, north of the Mojave Desert in southern California. The average spacing between Global Navigation Satellite System (GNSS) stations around the earthquakes is 20–30 km, insufficient to constrain the rupture details of the earthquakes. Here, we use Sentinel-1 and COSMO-SkyMed (CSK) Synthetic Aperture Radar data to derive the high-resolution coseismic and early postseismic surface deformation related to the Ridgecrest earthquake sequence. Line of sight (LoS) Interferometric Synthetic Aperture Radar displacements derived from both Sentinel-1 and CSK data are in good agreement with GNSS measurements. The maximum coseismic displacement occurs near the Mw 7.1 epicenter, with an estimated fault offset of ∼4.5 m on a northwest-striking rupture. Pixel tracking analysis of CSK data also reveals a sharp surface offset of ∼1 m on a second northwest-striking fault strand on which the Mw 6.4 foreshock likely nucleated, which is located ∼2–3 km east of the major rupture. The lack of clear surface displacement across this fault segment during the Mw 6.4 event suggests this fault might have ruptured twice, with more pronounced and shallow slip during the Mw 7.1 mainshock. Both Sentinel-1 and CSK data reveal clear postseismic deformation following the 2019 Ridgecrest earthquake sequence. Cumulative postseismic deformation near the Mw 7.1 epicenter ∼2 months after the mainshock reaches ∼5 cm along the satellites’ LoSs. The observed postseismic deformation near the fault is indicative of both afterslip and poroelastic rebound. We provide data derived in this study in various data formats, which will be useful for the broad community studying this earthquake sequence.

Segmented Thrust Faulting: Example From the Northeastern Margin of the Tibetan Plateau

AbstractSeismogenic faults are commonly composed of a series of segments, revealed by geometric barriers and along‐strike gradients in fault activity. At the northeastern margin of the Tibetan Plateau, the Minle‐Damaying Fault (MDF), bounding a portion of the eastern Qilian Shan, illustrates segmented paleoseismic behavior of a major seismogenic reverse fault. Field surveys, trench excavations, and drone‐surveyed topography along the MDF reveal scarps with diverse cumulative displacements. Multiple events, with timing constrained by radiocarbon dating, are identified by both trench exposures and analysis of deformed landforms. Both individual coseismic displacements and slip rates taper toward the ends, revealing repeated rupture of the western MDF segment. Not all events present at the center of this segment appear at sites closer to the fault tips, suggesting that some earthquakes did not everywhere rupture to the surface. Isolated rupture of the western segment would produce aMw7.0 earthquake. However, we cannot rule out correlation of some paleo‐earthquakes between two segments, corresponding to larger events. A cluster of two 7‐m slip events occurred on the eastern segment in the past 1,000 years, one of which may correspond to a multisegment event.

Seismicity, Fault Slip Rates, and Fault Interactions in a Fault System

AbstractSeismicity and the partitioning of slip rates in interacting and mechanically coupled fault systems are poorly understood. We developed and used three‐dimensional viscoelastoplastic finite element models to simulate earthquakes, earthquake cycles, and synthetic seismicity in single and bifurcated fault systems and investigate seismicity, fault slip rates, and interactions and mechanical coupling between faults in fault systems. The modeled interseismic velocities and coseismic displacements are consistent with those from analytical and quasi‐analytical solutions. We found that the modeled frequency‐magnitude relation satisfies the Gutenberg‐Richter relation and the b value is inversely related to differential stress. We observed that the seismicity on two parallel faults is often interdependent and complementary: high seismic moment release rates on a fault are usually accompanied by low ones on the other fault and vice versa; the two faults collectively accommodate far‐field tectonic loading and crustal relative motion. Model results showed that when two parallel faults have the same or similar strength, they have similar seismicity and long‐term slip rates, but when one of the two faults has lower strength, it has more active seismicity and a faster slip rate than the other; the sum of their slip rates equals the far‐field crustal relative motion in both cases. The results in this study provide scientific insights into the spatiotemporal migration of seismicity and partitioning of fault slip rates in an interacting and mechanically coupled fault system and help to qualify b values and to evaluate the earthquake hazard and risk on each of the faults in such a system.

Coseismic Displacements and Surface Fractures from Sentinel-1 InSAR: 2019 Ridgecrest Earthquakes

Abstract Interferometric Synthetic Aperture Radar is an important tool for imaging surface deformation from large continental earthquakes. Here, we present maps of coseismic displacement and strain from the 2019 Ridgecrest earthquakes using multiple Sentinel-1 images. We provide three types of interferometric products. (1) Standard interferograms from two look directions provide an overview of the deformation and can be used for modeling coseismic slip. (2) Phase gradient maps from stacks of coseismic interferograms provide high-resolution (∼30 m) images of strain concentration and surface fracturing that can be used to guide field surveys. (3) High-pass filtered, stacked, unwrapped phase is decomposed into east–west and up–down, south–north components and is used to determine the sense of fault slip. The resulting phase gradient maps reveal over 300 surface fractures, including triggered slip on the Garlock fault. The east–west component of high-pass filtered phase reveals the polarity of the strike-slip offset (right lateral or left lateral) for many of the fractures. We find a small number of fractures that have slip polarity that is retrograde to the background tectonic stress. This is similar to observations of retrograde slip observed near the 1999 Mw 7.1 Hector Mine rupture, but the Ridgecrest observations are more completely imaged by the frequent and high-quality acquisitions from the twin Sentinel-1 spacecrafts. Determining whether the retrograde features are triggered slip on existing faults, or compliant fault deformation in response to stress changes from the Ridgecrest earthquakes, or new Coulomb-style failures, will require additional field work, modeling, and analysis.

Coseismic Rupture Geometry and Slip Rupture Process During the 2018 Mw 7.1 Anchorage, South‐Central Alaska Earthquake: Intraplate Normal Faulting by Slab Tear Constrained by Geodetic and Teleseismic Data

AbstractThe Mw 7.1 Anchorage earthquake on 30 November 2018 beneath the south‐central Alaska is a rare intermediate‐depth event larger than Mw 7 that occurred in a complex subduction region, where the young Yakutat oceanic terrane wedges in the continental‐oceanic plate collisional region between the Pacific oceanic plate and the North American plate. We use both ascending and descending Sentinel‐1 satellite Interferometric Synthetic Aperture Radar (InSAR) images to construct the coseismic displacement associated with this earthquake, which shows a nearly circular deformation pattern with a subsidence of ~4 cm in line of sight direction. Combining coseismic GPS data, we determine the focal mechanism of this event dominated by normal faulting with N‐S striking of 186°and westward dipping of 64°by using a uniform slip model. Then we find a preferred slip model with both geodetic data and teleseismic data, suggesting the main slips are concentrated on a depth of 55–75 km. The total released moment of our preferred slip model is 5.32 × 1019N·m, equivalent to Mw 7.1. The rupture process includes two peaks terminating at about 18 s and indicates a unilateral rupture with its front propagating northwestward direction at an average speed of 2.5 km/s. In comparison with the detailed seismic image in this region, this event just occurred in the Yakutat terrane beneath a low velocity zone, suggesting it was caused by slab tear but not slab boundary breaking and determining the lower boundary of shallow thrust‐slip in the Alaska subduction zone.

Real-Time Seismic Waveforms Estimation of the 2019 MW = 6.4 and Mw = 7.1 California Earthquakes With High-Rate Multi-GNSS Observations

Global Navigation Satellite System (GNSS) is recognized as an effective tool to retrieve high-precision seismic displacements, which has been widely used in earthquake early warning systems such as magnitude estimation and fault slip inversion. In this study, we present two multi-GNSS positioning models for rapidly capturing real-time coseismic displacements using the raw pseudorange, carrier phase and Doppler measurements, called constant velocity (CV) and constant acceleration (CA) dynamic precise point positioning (PPP) models, respectively. The proposed methods are validated with the datasets collected during the 2019 July 4 Mw 6.4 and July 6 Mw 7.1 earthquakes in real-time scenarios. Results show that the two models can provide accurate displacement waveforms with the accuracy of few centimeters. Besides, the multi-GNSS integration can significantly improve the model performances compared with GPS-only solutions in both time- and frequency- domains. The dynamic PPP models can also reliably recover the moment magnitudes and permanent seismic displacements, indicating that the methods have the potential to benefit for earthquake early warning and rapid geohazard assessment.

A non-uniform dip slip formula to calculate the coseismic deformation: Case study of Tohoku Mw9.0 Earthquake

AbstractThe distribution of slip faults along the fault plane plays a special role in the kinetic pattern of tectonic deformation. To better understand the coseismic deformation and geodynamics of the earthquake, this paper applied the pile-up theory and derived an analytical formula to describe the non-uniform slip distribution along the fault width. To validate the new formula, it was tested with the coseismic displacements at the global positioning system (GPS) stations for the Tohoku earthquake in 11 March, 2011. Then, the computed horizontal and vertical displacements calculated using NDSM were compared to back-slip model (BSM) using GPS data obtained from the Jet Propulsion Laboratory (JPL). Finally, the theoretical analysis revealed that the analytical formulas derived here can be perceived as the expansion and perfection of the uniform dislocation model. Meanwhile, our results showed that the characteristics of the spatial distribution deformation from NDSM are similar to those derived by GPS measurements. Furthermore, the near-field RMS errors indicated that the horizontal displacements estimated using NDSM is 27.5%, and 35.6% for the vertical components. Our new formulas and findings could assist better portray the crustal deformation in some region and geodynamics in specific earthquake.

Coseismic Displacement Accumulation Between 1996 and 2019 Using A Global Empirical Law on Indonesia Continuously Operating Reference Station (InaCORS)

Indonesia archipelago is one of the most populated country with active and complex tectonic zone in the world. Plate boundaries were assembled by four major plate which made the region not only vulnerable to earth-hazard but also prone to semi-dynamic reference frame. However, influence of transient deformation such as coseismic displacement due to large amount of small to intermediate earthquakes (< Mw 6) on the geodetic networks is remain poorly understood. Geospatial Information Agency occupied permanent and continuous GPS networks since 1996 but rapidly increase in 2010. Based on simulated empirical law of coseismic crustal deformation, we estimate the cumulative displacement due to coseismic step on Indonesia Continuous Operating Reference Stations (InaCORS). We utilize the position of the observation network and earthquake hypocentral with estimated moment magnitude. Our result suggesting small to intermediate earthquakes are indispensable for estimating secular motion and potentially contribute the cumulative offset associated with the transient postseismic deformation.

The influence of topography and crustal heterogeneity on coseismic deformation of the 2008 Mw7.9 Wenchuan Earthquake, China

The Longmen Shan Thrust Belt, which lies at the convergence of the eastern Tibetan Plateau and Sichuan Basin, is characterized by a topographic relief of 4000 m over a distance of 100 km. While the rock underlying the Sichuan Basin is strong, the crust underlying the Tibetan Plateau is weak. Four models that simulate deformation caused by distributions of dislocations along a geometrically complex fault system are developed to investigate how the contrast in elevational and crustal heterogeneity influences coseismic deformation of the 2008 Mw7.9 Wenchuan earthquake. The models are configured with an assembly precise ramp-décollement structures and planar fault geometries. The coseismic slip distribution is estimated by inverting three component GPS observations with Green's functions calculated for each model configuration. By comparing the slip distribution and residuals among the displacement predictions from these four models and measurements of GPS, the crustal heterogeneity model robustly explained most of the observed GPS horizontal and vertical coseismic displacements. Results revealed four composite dislocation asperities distributed in the shallow crust and a slip of 4–8 m on the sub-surface décollement fault with a depth of ~20 km. The resulting geodetic moment is 8.10 × 1020 Nm, which is in agreement with the seismological estimates. The deep slip predictions obtained with the ramp-décollement fault geometry indicate that the eastern Tibetan Plateau was thrust over the Sichuan Basin rather than the plateau being uplifted owing to the underlying weak crust.

Fault weakening caused by smectite swelling

The large slip along the shallow subduction interface during the 2011 Tohoku-Oki earthquake (Mw9.0) caused a huge tsunami that struck the northeast coast of Honshu, Japan. The Integrated Ocean Drilling Program Expedition 343 JFAST program revealed that the fault zone is composed primarily of smectite. Our swelling experiments using the fault material demonstrated that the swelling pressure systematically increases with a decrease in sample porosity. Based on in situ porosity estimations in the IODP borehole, the swelling pressure of the fault is as high as 8 MPa, which is comparable to the effective normal stress at the drill site (~ 7 MPa). This also suggests that the modified effective confining pressure of the fault is quite low or potentially zero, meaning that fault strength is governed mainly by cohesion rather than frictional strength. The fault may therefore be intrinsically weak, which could enhance the coseismic displacement toward the trench when earthquake slip propagates from depth.

ОХОТОМОРСКОЕ-III ЗЕМЛЕТРЯСЕНИЕ 24 мая 2013 г. с Mwрег=8.3, I0=6 (Охотскоеморе)

The strongest deep earthquake on May 24, 2013 (Mwreg=8.3) is discussed. It occurred under the Sea of Okhotsk at a depth of about 630 km. The instrumental hypocenter location reported by the KB GS RAS is φ=54.75N, λ=153.78E, h=630 km. Three magnitudes were obtained: local magnitude ML=7.8, code-wave magnitude Mc=7.6, moment magnitude Mwreg=8.3. The Okhotsk earthquake hypocenter is located on the northern part of the ancient slab, practically at the lower end of the seismogenic region. The earthquake caused significant co-seismic displacements at most GNSS observation points. The earthquake focal mecha-nisms solutions have been obtained by three ways. The solutions are very similar. The submeridial hollow falling nodal plane seems more preferable. For the deep quake of May 24, 2013, a series of aftershocks were registered. The aftershock process had three consistent stages with different decay character. The cloud of deep-focus aftershocks has the 400200 km size, with the 450–700 km depth range and is extended in the North–South direction. The aftershock process has the three-phase character and can be considered as a stream of seismic events decreasing in time with three successive stages with different attenuation modes. The change in attenuation modes is associated with strong aftershocks. The duration of the decaying after-shock process is ~ 280 days. The anomalous distribution of impact was observed for the earthquake: 1) a large range of macroseismic effect – quake was felt throughout the World; 2) in the territory of Kamchatka, maximum shakes and ground motions were observed at the points located on the eastern coast of Kamchat-ka, and at comparable northern and western distances macroseismic and instrumental intensities were lower. Despite the globality of the macroseismic effect, in the nearest settlements (Kamchatka region), the earth-quake was felt with intensity up to 5–6 and caused no damage. The May 24, 2013 earthquake produced many strong motion records. The ground motion characteristics such as peak amplitudes of motion, spectral shape and response spectrum were received using the records of the earthquake from Kamchatka network of digital accelerographs.

The seismogenic source on the deep lateral ramp of Sumatra accretionary wedge inferred from the source model of the 2009 mw 7.6 Padang, Indonesia, earthquake

The 2009 Mw 7.6 Padang earthquake has been inferred as an intraslab event because it locates at approximately 80 km depth which is within the oceanic slab with maximum curvature. However, the major trench-parallel-striking normal faulting event usually occurs at this tectonic environment but not the trench-normal-striking reverse event like this 2009 Padang earthquake. To solve this enigma, the coseismic displacements were estimated based on the analysis of daily coordinate time series calculated by GAMIT software from 15 continuous GPS stations along the Sumatra region. The maximum horizontal displacement is approximately 58.3 mm toward SW at the MSAI station while the maximum vertical displacement reaches 16.1 mm. The optimized geometry parameters of the source fault were determined by the Markov Chain Monte Carlo using the uniform-slip dislocation model. The optimized strike and dip of fault plane are 80circ and 57circ, respectively. The coseismic slip distribution was then estimated using the distributed-slip dislocation model in terms of optimized fault geometry. The geodetic moment of 1.35 x 1027 dyne-cm in our best-fit model is equivalent to Mw 7.39. The coseismic slip mainly ranges 28-70 km in depth with the maximum slip of 2000 mm. The optimized source fault plane is also comparable to the relocated aftershock distribution. Comparing to the location of interface, our source fault is mainly located at the place above the interface. We therefore proposed that this 2009 Padang earthquake occurred in the deep part of accretionary wedge, but not with the slab. In addition, we also proposed this 2009 event as a lateral ramp event because its strike is normal to the trench, such as the 2010 Jaishian earthquake in Taiwan. Finally, we proposed that a thick-skinned deformation may be also represented in the prism of Sumatra subduction zone.

Seismogenic fault and tectonic significance of 1996 Karakoram Pass earthquake (Ms 7.1) based on InSAR

Due to hard observation condition of the western Tibet region, the slip behaviors of the Ms7.1 Karakoram Pass earthquake occurred in Hetian, Xinjiang on November 19, 1996 remains unclear. Using ERS 1/2 SAR data and InSAR technique, we obtain the co-seismic deformation of the earthquake. The north and south deformation areas show asymmetric pattern, with the maximum LOS displacement of the southern part approximately 24.6 cm, and the maximum LOS displacement in the northern part approximately − 18.5 cm. Nonlinear and linear inversion algorithms are used to determine the geometric parameters and slip distribution of the earthquake fault. Our results show that the co-seismic displacement is dominated by deformation fields are clearly visible sinistral strike-slip accompanied by a small amount of normal slip component. The co-seismic slip occurred between 0 and 18 km at depth. The maximum slip is ~ 81 cm, occurring at a depth of 8.5 ± 0.5 km at (35.36°N 78.03°E), indicating a shallow event with a moment magnitude of Mw 6.5. The seismogenic fault is a secondary fault in the Karakoram fault zone with strike 96°, dip 84°, and rake – 24°. This earthquake shows that the Karakoram fault zone undergoes a complex tectonic deformation process, with central part of the fault zone showing minor tensional deformation behaviors.

Mapping the geology of the 2016 Central Italy earthquake fault (Mt. Vettore – Mt. Bove fault, Sibillini Mts.): geological details on the Cupi – Ussita and Mt. Bove – Mt. Porche segments and overall pattern of coseismic surface faulting

We present the results of a field survey performed in the centralnorthern portion of the Mt. Vettore – Mt. Bove normal fault(VBF), reactivated during the 2016 central Italy earthquake sequence (24 August, Mw 6.0; 26 October Mw5.4 and Mw 5.9; 30 October Mw 6.5). The field survey was carried out by means of digital mapping techniques, and traditional methods on 1:10,000-scale topographic maps. The field work had two main aims: 1) to detail the geology of the central-northern VBF, and to constrain the segmentation and displacement distribution of the entire VBF system; and 2) to map in detail the ruptures of the 26 and 30 October events, filling in the gaps left by previous studies, and provide constraints on the coseismic parameters of the 2016 earthquakes.The results are summarized in a composite geological map, organized in 8 frames showing: the structural architecture in map view of the VBF system (frames 1 and 2); 1:25,000-scale geological maps of the Cupi-Ussita (frame 3) and Mt. Bove – Mt. Porche (frame 4) sectors of the VBF; twelve 1:25,000-scale geological sections for computing the geological displacements (frame 5); a summary of the coseismic parameters of the 2016 earthquakes (diagrams of net displacement, throw and opening; Surface Rupture Length, SRL; Maximum Displacement, MD and Average Displacement, AD) (frame 6); a comparison of the 2016 coseismic parameters with normal faulting earthquakes occurred globally (frame 7); and a computation of the morphological displacement (post-Last Glacial Maximum, LGM) across the VBF, a comparison among geological, morphological and coseismic displacements, and a quantification of the tectonic back-tilting in the area of maximum coseismic displacement (frame 8). Some implications are discussed in this accompanying note, such as the role of fault segmentation deduced from structural geology and tectonic geomorphology in controlling the coseismic displacement, the role of back-tilting in amplifying the coseismic displacement and the limits of empirical regressionsin predicting the relations between rupture parameters and Mw in case of segmented normal faults.

A physics-based approach of deep interseismic creep for viscoelastic strike-slip earthquake cycle models

SUMMARYMost geodetic inversions of surface deformation rates consider the depth distribution of interseismic fault slip-rate to be time invariant. However, some numerical simulations show downdip penetration of dynamic rupture into regions with velocity-strengthening friction, with subsequent updip propagation of the locked-to-creeping transition. Recently, Bruhat and Segall developed a new method to characterize interseismic slip rates, that allows slip to penetrate up dip into the locked region. This simple model considered deep interseismic slip as a crack loaded at its downdip end, and provided analytical expressions for stress drop within the crack, slip and slip rate along the fault. This study extends this approach to strike-slip fault environments, and includes coupling of creep to viscoelastic flow in the lower crust and upper mantle. I use this model to investigate interseismic deformation rates along the Carrizo Plain section of the San Andreas fault. This study reviews possible models, elastic and viscoelastic, for fitting horizontal surface rates. Using this updated approach, I develop a physics-based solution for deep interseismic creep which accounts for possible slow vertical propagation, and investigate how it improves the fit of the horizontal deformation rates in the Carrizo Plain region. I found solutions for fitting the surface deformation rates that allow for reasonable estimates for earthquake rupture depth and coseismic displacement and improves the overall fit to the data. Best-fitting solutions present half-space relaxation time around 70 yr, and very low propagation speeds, less than a metre per year, suggesting a lack of creep propagation.