Global Positioning System Velocity Research Articles

Comparison of Metabolic Power and Energy Cost of Submaximal and Sprint Running Efforts Using Different Methods in Elite Youth Soccer Players: A Novel Energetic Approach.

Sprinting is a decisive action in soccer that is considerably taxing from a neuromuscular and energetic perspective. This study compared different calculation methods for the metabolic power (MP) and energy cost (EC) of sprinting using global positioning system (GPS) metrics and electromyography (EMG), with the aim of identifying potential differences in performance markers. Sixteen elite U17 male soccer players (age: 16.4 ± 0.5 years; body mass: 64.6 ± 4.4 kg; and height: 177.4 ± 4.3 cm) participated in the study and completed four different submaximal constant running efforts followed by sprinting actions while using portable GPS-IMU units and surface EMG. GPS-derived MP was determined based on GPS velocity, and the EMG-MP and EC were calculated based on individual profiles plotting the MP of the GPS and all EMG signals acquired. The goodness of fit of the linear regressions was assessed by the coefficient of determination (R2), and a repeated measures ANOVA was used to detect changes. A linear trend was found in EMG activity during submaximal speed runs (R2 = 1), but when the sprint effort was considered, the trend became exponential (R2 = 0.89). The EMG/force ratio displayed two different trends: linear up to a 30 m sprint (R2 = 0.99) and polynomial up to a 50 m sprint (R2 = 0.96). Statistically significant differences between the GPS and EMG were observed for MP splits at 0-5 m, 5-10 m, 25-30 m, 30-35 m, and 35-40 m and for EC splits at 5-10 m, 25-30 m, 30-35 m, and 35-40 m (p ≤ 0.05). Therefore, the determination of the MP and EC based on GPS technology underestimated the neuromuscular and metabolic engagement during the sprinting efforts. Thus, the EMG-derived method seems to be more accurate for calculating the MP and EC in this type of action.

Estimating the slip rate in the North Tabriz Fault using focal mechanism data and GPS velocity field

Abstract This study delves into slip distribution on the North Tabriz Fault (NTF), a critical aspect of seismic hazard analysis due to its proximity to the Tabriz metropolis. The study operates within a uniform elastic half-space, maintaining constant values for fault geometry and regional rheological parameters throughout the research. To calculate strain boundary conditions, permanent and periodic global positioning system (GPS) data from the northwest region were utilized. The fault was constrained perpendicularly while allowing tangential movement, facilitating the determination of its annual slip rate using the boundary element method, with the Okada analytical model serving as the fundamental solution. The findings underscore the intricate relationship between the fault’s slip rate and boundary conditions, revealing a predominant right-lateral strike-slip motion. The study offers two slip rate assessments, obtained through earthquake focal mechanisms and GPS velocity data, yielding values of 5 and 5.5 mm / year {\rm{mm}}/{\rm{year}} , respectively. Importantly, the alignment of these calculated slip rates with paleo-seismological data underscores the credibility of the results generated via the boundary element method, distinguishing it as a reliable approach when compared to other numerical and analytical techniques. This research provides valuable insights into the behavior and slip dynamics of the NTF, which is pivotal for assessing seismic risks.

A pressure solution flow law for the seismogenic zone: Application to Cascadia.

We develop a linear viscous constitutive relationship for pressure solution constrained by models of deformed metasedimentary rocks and observations of exposed rocks from ancient subduction zones. We include pressure and temperature dependence on the solubility of silica in fluid by parameterizing a practical van't Hoff relationship. This general flow law is well suited for making predictions about interseismic behavior of subduction zones. We apply the flow law to Cascadia, where thermal structure, geometry, relative plate velocity, and Global Positioning System velocity field are well constrained. Results are consistent with the temperature conditions at which resolvable ductile strain is recorded in subducted mudstones (at depths near the updip limit of the seismogenic zone) and with relative plate motion accommodated completely by viscous deformation (at depths near the downdip limit of the seismogenic zone). The flow law also predicts the observed forearc tapering of slip rate deficit with depth.

Spatiotemporal Characteristics of Horizontal Crustal Deformation in the Sichuan–Yunnan Region Using GPS Data

Based on various velocity fields from Global Positioning System (GPS) data over nearly 20 years in the Sichuan–Yunnan region, this paper calculated the strain rate field and its spatiotemporal characteristics by using an improved least squares collocation method. We evaluated the calculated strain field by extensively discussing the impact of non-tectonic factors on the calculation. Subsequently, we described the present-day strain rate features and their spatiotemporal variations. The results indicate the necessity of considering the influence of non-tectonic factors when calculating the strain rate field by using GPS velocity data. Widespread strain accumulation is observed in the Sichuan–Yunnan region, and significant second strain rate invariant with an average value of 33.1 nanostrain/yr primarily occurs along the eastern boundary faults of the Sichuan–Yunnan rhomboid block, specifically the Xianshuihe–Anninghe–Zemuhe–Xiaojiang fault systems. These fault systems also demarcate the zones with negative and positive dilation strain. According to the spatiotemporal variations of strain rate fields, the northern and southern segments of the Xianshuihe Fault, the Anninghe Fault and its eastern adjacent faults, and the Xiaojiang Fault are undergoing intensifying strain. Consequently, these zones should be paid more attention due to their relatively higher seismic risk in the Sichuan–Yunnan region.

Peak Ground Velocity (PGV) estimation of Mw 5.6 Cianjur earthquake November 11, 2022 using Global Positioning System (GPS)

The primary purpose of GPS is to be used for positioning, navigation, and timing (PNT). In the last decade, research on GPS for earthquake hazards has increased rapidly, such as for tectonic deformation, GPS seismology, modeling earthquake source parameters, estimation of magnitude, etc. In this study, following the Mw 5.6 Cianjur earthquake on November 11, 2022, we estimate the peak ground velocity from the CJUR GPS station, which is located about 15 km from the epicenter. We compute GPS velocity from the high-rate GPS receiver independent exchange (RINEX) data and broadcast ephemeris. Using a narrow line combination of L1 and L2 observations, we invert velocity epoch by epoch. The result shows the CJUR GPS station has a peak ground velocity of about 11.5 cm/s and equal to VI MMI scale. The peak ground velocity from the GPS station could be important for deriving the earthquake shakemap. By increasing the number of GPS stations in Indonesia, it is very important to support earthquake hazard monitoring.

Characteristics of Regional GPS Crustal Deformation before the 2021 Yunnan Yangbi Ms 6.4 Earthquake and Its Implications for Determining Potential Areas of Future Strong Earthquakes

The 2021 Yangbi Ms 6.4 earthquake in Yunnan, China, occurred in an area where the Global Positioning System (GPS) geodetic observations are particularly intensive. Based on a detailed retrospective analysis of the GPS observations of about 133 stations distributed in the proximately 400 km × 400 km region that contains the area affected by the earthquake., we obtain a high-resolution GPS velocity field and strain rate field and then derive the present-day slip rates of major faults in the region with the commonly used half-space elastic dislocation model and constraints from the GPS velocity field. Furthermore, by calculating the seismic moment accumulation and release and deficit rates in the main fault segments and combining with the distribution characteristics of small earthquakes, we evaluate the regional seismic risk. The results show that (1) there was a localized prominent strain accumulation rate around the seismogenic area of the impending Yangbi Ms 6.4 earthquake, although this was not the only area with a prominent strain rate in the whole region. (2) The seismogenic area of the earthquake was just located where the strain direction was deflected, which, together with the localized outstanding maximum shear strain and dilatation rates, provides us with important hints to determine the potential areas of future strong earthquakes. (3) Of all the seismogenic fault segments with relatively high potentials, judged using the elapsed time of historical earthquakes and effective strain accumulation rate, the middle section of the Weixi–Qiaohou fault has a higher earthquake risk than the southern section, the Midu–Binchuan section of the Chenghai fault has a higher risk than the Yongsheng section and the Jianchuan section of the Jianchuan–Qiaohou–Lijiang–Xiaojinhe fault has a higher risk than the Lijiang section.

The 2021MW 6.2 Mamuju, West Sulawesi, Indonesia earthquake: partial rupture of the Makassar Strait thrust

SUMMARYOn the 2021 January 15 (local date), an MW 6.2 earthquake struck the Mamuju and Majene regions of West Sulawesi, Indonesia. This event killed more than 100 inhabitants, leaving at least 30 000 people displaced from their homes, and damaged almost 8000 buildings within a radius of ∼30 km from the main shock's epicentre location (as shown on our damage proxy map). This event was generated by an active fault that continues to the Makassar Strait Thrust (MST) offshore West Sulawesi. The hazard potential of this fault remains poorly understood. In this study, we use seismic and Global Positioning System (GPS) data to investigate the source characteristics of the main shock. The results suggest that the main shock partially ruptured one segment of the MST, activated a secondary fault structure, and likely brought the updip unruptured section of the MST segment closure to failure. Our analysis of interseismic GPS velocities indicates that the Mamuju and Majene regions have a higher crustal strain rate than other nearby regions. The results (partial rupture of the MST segment, the updip unruptured section of the MST and high strain rate in the Mamuju and Majene regions) together suggest a significant seismic hazard potential in West Sulawesi, particularly in the Mamuju and Majene areas.

Ensemble Clustering in GPS Velocities: A Case Study of Turkey

Block modeling is an effective way to understand Earth’s crustal deformation. However, the choice of block boundaries and the number of blocks affect the model results. Therefore, the subjectivity of this analysis should be avoided. Clustering analysis can be used to define the blocks of GPS (Global Positioning System) velocity fields without a priori information. Unfortunately, clustering methods also have unique solutions and differ with various algorithms. Ensemble methods could be an answer to enhance the clustering results for GPS velocities. In this study, we use ensemble clustering to identify block boundaries before block modeling without a priori information about the data. The ensemble clustering method is used for the first time in the clustering of GPS velocities and the case of Turkey is discussed. The published horizontal GPS velocities were first clustered with five different clustering methods and the optimum classes were determined using ensemble clustering methods. It is proven that the Meta-CLustering Algorithm can be used in terms of ensemble clustering for this region.

Two-layer model of anisotropy beneath Myanmar and Thailand revealed by shear-wave splitting

The first model of two layers is presented to study the anisotropy pattern beneath Myanmar and Thailand using shear-wave splitting. Teleseismic activity recorded by 15 permanent broadband stations was analysed to investigate the anisotropy and to understand the flow direction in the mantle. The flow direction and speed were observed in the forms of fast polarisation direction (𝜙) and delay time (𝛿𝑡) between fast and slow components. The measurements showed that a two-layer model beneath stations better explicates the splitting observations than a single-layer model. The upper and lower layers were interpreted as lithosphere and asthenosphere in similar patterns and compared with GPS (Global Positioning System) velocity fields and strain rate fields. Two groups of 𝜙 can be classified and matched with West-Burma Terrane (WBT) and Shan-Thai Terrane (STT). The 𝜙 represents that West-Burma Terrane moves in a northward direction, Shan-Thai Terrane and Indo-China Terrane (ICT) move in a south-eastern direction, and West-Burma Terrane has less anisotropy of 𝜙 than Shan-Thai Terrane.

Evidence of structural transformation in the eastern part of the Altyn Tagh Fault, northern margin of the Tibetan Plateau, China, based on the kinematics and shortening rate of the Hongliuxia region

(a) Blocks distributed surround the Tibetan Plateau. (b) Active tectonics in the northeastern Tibetan Plateau. The black rectangle within the inset shows the study area. The thick grey line shows the block boundary. Blue arrows show the global positioning system (GPS) velocity with respect to the Eurasian Plate, and the green arrows represent the GPS velocity with respect to GAB. (c) Deformation rates of these faults and folds in the compressional stepover of the eastern ATF. JTF: Jinta Fault, HLF: Helishan Fault, LSF: Longshoushan Fault, NQLF: North Qilian Shan Fault, SS: sinistral strike-slip rate, Sh: shortening rate, V: vertical rate, HLX Fo.: Hongliuxia thrust-fold belt, HSG Anti.: Huoshaogou Anticline, NKTF: North Kuantanshan Fault, LJM Anti.: Laojunmiao Anticline, and BYF: Baiyang Fault. • Shortening rate of the Hongliuxia region was 0.7 ± 0.2 mm/yr in Late Pleistocene. • Hongliuxia region showed more N–S shortening than the W–E strike-slip. • Stepover was formed between the eastern Altyn Tagh fault and Jinta-Nanshan fault. The Altyn Tagh Fault (ATF) and the North Qilian Shan Fault, as the northern margin of the Tibetan Plateau, have always been the focus of attention while developing a propagation model of the plateau. However, rocks in the North Qilian Shan Fault are intensely deformed and understanding the deformation history is difficult. The ATF and North Qilian Shan Fault have propagated into the Hexi Corridor and led to a series of new faults and folds. Based on simple kinematics and insignificant deformations of these new faults and folds, the geological process can be easily understood. The Hongliuxia region, which represents a positive flower structure in the easternmost part of the ATF, is the binding transformation site between the ATF and North Qilian Shan Fault. In this study, the kinematics of the Hongliuxia region was determined based on structural profiling and fault surveys. The shortening rate (0.7 ± 0.2 mm/yr) was estimated from the deformation and 10 Be exposure age of fluvial terraces. We found that the ATF might be connected to the Jinta-Nanshan Fault by a compressional stepover on the northern part of the Yumen Basin, which transforms into a series of compressional ridges, including the Hongliuxia thrust-fold belt, Huoshaogou Anticline, and North Heishan Fault. We infer that the ATF and the Longshoushan Fault, which serve as boundary faults, might be linked by multiple compressional stepovers. The gradual changes of the striking angles by compressional stepovers indicated the transformation from strike-slip to compressional structures and these changes caused the two boundary faults (ATF and Longshoushan Fault) to jointly undergo crustal deformation associated with the northward propagation of the Tibetan Plateau. This study can advance our understanding of the relationship between ATF and the Qilian Shan thrust fault system.

A Fault-Based Crustal Deformation Model with Deep Driven Dislocation Sources for the 2023 Update to the U.S. National Seismic Hazard Model

Abstract A fault-based crustal deformation model with deep driven dislocation sources is applied to estimate long-term on-fault slip rates and off-fault moment rate distribution in the western United States (WUS) for the 2023 update to the National Seismic Hazard Model (NSHM). This model uses the method of Zeng and Shen (2017) to invert for slip rate and strain-rate parameters based on inputs from Global Positioning System (GPS) velocities and geologic slip-rate constraints. The model connects adjacent major fault segments in California and the Cascadia subduction zone to form blocks that extend to the boundaries of the study area. Faults within the blocks are obtained from the NSHM geologic fault section database. The model slip rates are determined using a least-squares inversion with a normalized chi-square of 6.6. I also apply a time-dependent correction called “ghost transient” effect to account for the viscoelastic responses from large historic earthquakes along the San Andreas fault and Cascadia subduction zone. Major discrepancies between model slip rates and geologic slip rates along the San Andreas fault, for example, from the Cholame to the Mojave and San Bernardino segments of the San Andreas, are well reduced after the ghost transient correction is applied to GPS velocities. The off-fault moment rate distribution is consistent with regional tectonics and seismicity patterns with a total rate of 1.6×1019 N·m/yr for the WUS.

Two kinematic transformations of the Pamir salient since the Mid-Cenozoic: Constraints from multi-timescale deformation analysis

The Pamir salient is a key part of the Himalayan–Tibetan Plateau orogenic system and has undergone intense tectonic deformation during the India–Asian collision. Delineating the Cenozoic kinematics and geodynamics of the Pamir salient requires a comprehensive understanding of the active arcuate structures along its frontal margin, from the perspective of the multi-spatiotemporal evolution of deformation patterns. Here, we reviewed the deformation rates of the major structures at different timescales, reanalyzed the published Global Positioning System velocities, and examined the present-day seismicity to constrain the kinematics of the Pamir salient since the Late Cenozoic. Integrated with the crustal evolution history during the Middle–Late Cenozoic and the deep structure, we proposed a new model to explain the multi-stage kinematics and associated geodynamics of the Pamir salient. During ∼37–24 Ma, the initial Pamir salient moved northward via radial thrusting that rotated the basins on both sides, which was driven by the continuous compression of the Indian slab after the breakoff of its oceanic part. During ∼23–12 Ma, the gravitational collapse of the Central and South Pamir crusts, which was induced by the breakoff of the continental part of the Indian slab, triggered the extension within the Pamir and foreland-ward movement of the upper crust. The upper crustal materials moved in varying directions due to the differential strength of the foreland areas, transforming the crustal kinematics from radial thrusting into a combination of radial thrusting and transfer faulting. Since the coupling of the Indian and Pamir slabs at ∼12–11 Ma, the deformation propagation towards the forelands accelerated, after which the kinematics of the Pamir salient exhibited asymmetric radial thrusting that has been sustained until the present. The asymmetric radial thrusting was likely driven by the compressive stress effect of the lithospheric basal shear generated by the underthrusting of the cratonic Indian lithosphere, which further led to the rollback of the Pamir slab and the consequent migratory extension in the South Pamir.

Late Cenozoic to Present Kinematic of the North to Eastern Iran Orogen: Accommodating Opposite Sense of Fault Blocks Rotation

The opposite-sense fault block rotation across the continental strike-slip faulting plays an important role in accommodating crustal deformation in the north of the East Iran orogen. This research constrains the post-Neogene kinematics of the NW-SE to E-W left-lateral transpressional zones at the northern termination of the N-S striking right-lateral Neh fault system in the East Iran orogen. Using two case studies, we analyzed the NW-SE Birjand splay and the E-W Shekarab transpression zone by analysis of satellite images, structural features, fault geometry and kinematics, GPS (Global Positioning System) velocities, fault- and earthquake-slip stress inversion, and paleomagnetic data. Our results show two distinctive regions of opposite-sense fault block rotations and with different rotation rates. As an asymmetric arc, the Birjand splay displays a transition from the prevailing N-S right lateral shear in the east to NW-SE left lateral transpression in the middle and E-W left lateral shear in the west. In the east, with clockwise fault block rotation, the N-S right lateral faults and the NW-SE oblique left-lateral reverse faults constitute push-ups through the restraining fault bends. In the west, with counterclockwise fault block rotation, the Shekarab transpression zone is associated with the duplex, pop-up, and shear folds. Our suggested kinematic model reveals that the N-S right-lateral shear is consumed on the left-lateral transpressional zones through the vertical axis fault block rotation. This led to an E-W shortening and N-S along-strike lengthening in the East Iran orogen. This research improves our understanding of how opposite fault block rotations accommodate India- and Eurasia-Arabia convergence in the north of the East Iran orogen. The suggested model has implications in the kinematic evolution of intra-plate strike-slip faulting through continental collision tectonics.

Comparative analysis of the optimum cluster number determination algorithms in clustering GPS velocities

SUMMARY The Global Positioning System (GPS), although it has existed for only 30 years, is an important source for active tectonics, resulting in estimates of plate motions very close to geologic estimates over millions of years. GPS is also used for elastic block models to calculate slip rates for a better understanding of Earth’s active crustal deformation. GPS-derived velocity fields may be used as the basis for clustering analysis to create a preliminary definition of block geometry. In this study, we used published horizontal velocity fields to evaluate the effects of data dependences on determining the optimum number of clusters with algorithms. For this purpose, we used different variations of velocity fields in Turkey and tested four different algorithms that are Davies–Bouldin index, the elbow method, GAP statistics algorithm and the silhouette method. We also clustered velocity components with the k-means technique and compared the results with previous studies.

“Ghost Transient” Corrections to the Southern California GPS Velocity Field from San Andreas Fault Seismic Cycle Models

Abstract Seismic cycle models of the northern and southern San Andreas fault (SAF) were developed to estimate corrections for viscoelastic transients embedded in the present-day Global Positioning System (GPS) velocity field. These models incorporate a viscous shear zone embedded in either a layered or a 3D viscoelastic structure. In the southern SAF model, the 3D effective viscosity structure is based on the Southern California Earthquake Center (SCEC) community rheology model (CRM) and the SCEC community thermal model. Viscoelastic materials are represented with Burgers or Maxwell viscoelastic rheologies, and ranges of rheological parameters and earthquake chronologies are explored. For the northern and southern SAF models, surface velocity perturbations or “ghost transients” (GTs) of up to 3.5–6 mm/yr are obtained for a wide range of conditions. In all cases, the GT velocities are consistent with left-lateral rather than right-lateral motion across the SAF, and subtracting them from the present-day GPS velocity field increases the apparent SAF offset rate. For the southern SAF model, GT velocities are fairly insensitive to the timing of large SAF earthquakes prior to 1857, but they are sensitive to rheology (i.e., temperatures and strain rates assumed for computing CRM effective viscosities). For the northern SAF model, GT velocities are sensitive to both rheology (mantle, lower crust and shear zone effective viscosities, and Burgers Body parameters Δb and RB) and mean earthquake recurrence interval. For the reference northern and southern SAF models provided to U.S. Geological Survey National Seismic Hazard Mapping Project deformation modelers, the maximum GT velocities are 3.73 and 4.84 mm/yr, respectively.

Stress and Strain Characteristics before the Mw 7.3 Maduo Earthquake and Its Implications for Future Earthquakes on the Maqin–Maqu Fault

ABSTRACT To determine the crustal deformation and the stress–strain accumulation characteristics preceding the Mw 7.3 Maduo earthquake and the seismic potential of the Maqin–Maqu fault segment, the seismic data from small earthquake events and Global Positioning System (GPS) observations stations are collected. The b-value, the GPS velocity field, the GPS baseline, and the GPS strain parameters for multiple areas are calculated and analyzed. The results show a low b-value anomaly in the epicenter and its adjacent areas before the earthquake, which suggest that the stress level of the medium in this area was high before the earthquake. The regional GPS velocity field indicates that the earthquake epicenter is in an area where strain energy accumulates at varying slip rates and orientations. The deformation rates of the northeast-oriented baselines on the east side of the fault and the northwest-oriented baselines on the west side of the fault are lower than those observed near the three near north–south-oriented baselines, reflecting a small compressive deformation that occurred at the epicenter before the earthquake. Meanwhile, the motion of baselines QHYS-QHMD, QHYS-QHMQ, and QHGE-SCSP noticeably decreased, indicating that the area near the fault had already stored a great deal of strain energy prior to the earthquake. The rate of plane strain reduced in the epicenter region before the earthquake gradually since the second half of 2019, illustrating the deficit points to high stress conditions in the epicenter area. Furthermore, the area near the epicenter was characterized by high strain accumulation before the earthquake. The Maqin–Maqu segment of the East Kunlun fault is likely to be capable of generating strong earthquakes in the near future, because the current state of the area is similar to that of the Maduo epicenter before the onset of the earthquake.

Improve the accuracy of vehicle velocity estimation based on low-cost GPS/IMU by GPS course angle

Vehicle velocity is an important parameter for vehicle dynamics control. Global Positioning System (GPS) and inertial measurement unit (IMU) information can be used for velocity estimation by taking advantage of each other through fusion. However, if GPS velocity is used as the only measurement like classic GPS/INS, it will cause a large velocity estimation error or even divergence. This paper, from the perspective of system observability, proves that the GPS course angle (GCA) plays an important role in vehicle velocity estimation based on low-cost GPS/IMU. Firstly, construct the velocity estimation algorithm in the vehicle coordinate system directly. Then, according to the characteristics of different working conditions, the observability of the system without GCA is fully analyzed from the Lie derivative-based observability proof and the observability basic definition. The results show that the weak observability of the yaw angle is the most serious threat in vehicle velocity estimation. After fusing the GCA, the yaw angle potential divergence can be suppressed and the estimation accuracy of velocity will be improved. Even though roll and pitch are still unobservable under some conditions after augmenting GCA, the error propagation analysis shows that their estimation errors have little effect on velocity estimation, so the accurate estimation of velocity can be guaranteed. Finally, the indispensable of GCA in velocity estimation based on low-cost GPS/IMU is verified by Carsim-Simulink joint simulations and vehicle tests.

Deep Electrical Structure of the Langshan Mountain-Linhe Basin Area on the Northwest Edge of the Ordos Block, China

A series of fault depression structures have developed around the Ordos Block. The Langshan Mountain-Linhe Basin area (LLA), located on the northwest edge of the Ordos Block, is a typical, normal tension fault system. A geological survey shows that the Langshan Piedmont fault (LPF) in this area has a large slip rate and indicates risk of earthquake preparation. Broadband magnetotelluric (MT) exploration research was recently carried out across the LLA in the NW–SE direction, and the three-dimensional deep electrical structure thus obtained revealed that the LPF in the LLA is an evident electrical boundary zone on the whole crustal scale and is the main boundary fault of the primary structural block of the Alxa and Ordos Blocks. The MT results also show that the Linhe Basin and Ordos Block belong to the same tectonic basement. The Linhe and Dengkou faults belong to the internal faults of the Ordos Block. The upper crust of the Langshan Mountain on the west side of LPF is characterized by high-resistivity, the middle and lower crust have a low-resistivity layer, and the Linhe Basin on the east side has a Cenozoic low-resistivity sedimentary layer of approximately 10 km thick, which reveals that the Linhe Basin is a faulted basin with sedimentary thickness around the Ordos Block. This indicates that the LLA has experienced continuous and strong tension, normal fault depression sedimentary activities since the Cenozoic era. The current Global Positioning System velocity field shows that there is an apparent NW–SE acceleration zone in the LLA. The leveling data indicate that Linhe Basin shows a subsidence trend relative to the Ordos Block, indicating that the area is undergoing continuous NW–SE tension and faulting. It is speculated that there is a risk of earthquake preparation in the LPF.

Acceleration of Deep Slip Along the Longmenshan Fault Plane Before the 2008 M8.0 Wenchuan Earthquake

The first step toward earthquake forecasting is the identification of variables whose spatio-temporal variation can be connected with pre-seismic crustal deformation. Four periods of campaign Global Positioning System (GPS) observations around the Longmenshan fault zone (LFZ) provide important insights in crustal deformation and deep fault slip before the 2008 M8.0 Wenchuan earthquake. By using TDEFNODE to invert the coupling fraction and dynamic slip deficit rate of the Longmenshan fault plane before the Wenchuan earthquake, we show that under a background of strong coupling, the compressive slip deficit rate perpendicular to fault increased slightly at first and then decreased; a value of ∼1.5–3.6 mm/a along the central–southern segment from 1999 to 2001 increased to ∼1.9–3.9 mm/a from 2001 to 2004, and then decreased to ∼1.1–2.6 mm/a from 2004 to 2007. The dextral slip deficit rate parallel to fault was ∼6 mm/a from 1999 to 2004, before increasing significantly to ∼9.5 mm/a from 2004 to 2007, when the compressive slip deficit rate decreased. At the same time, large-scale GPS velocity profiles show that compressive shortening deformation in the Eastern Tibet Block, perpendicular to fault, increased slightly from 2001 to 2004, and then decreased from 2004 to 2007. Meanwhile, the dextral shear deformation parallel to fault near the LFZ increased significantly from 2004 to 2007. These findings are in good agreement with those calculated using repeating earthquake sequences, indicating that the deep slip rate of the Longmenshan fault plane may have accelerated several years before the Wenchuan earthquake. Our results demonstrate that GPS data can record pre-seismic preparatory processes, and have the potential for use in medium-term large earthquake forecasting.

Analysis of Tectonic Plate Velocity Variations in the Sunda Strait Based on GPS Time-series Data

Indonesia is an earthquake-prone country located in the junction of four tectonic plates, namely the Indo-Australian, Eurasian, Philippine, and Pacific. The convergent boundary between tectonic plates is also called a subduction zone that can produce great earthquakes in the future. One of the subduction zones in Indonesia is the Sunda Strait subduction zone which predicted can release a M7.8 earthquake. Previous research stated that there is a change in tectonic plate velocity after an earthquake ruptured. It is likely that this could happen in the Sunda Strait area which has experienced several large earthquakes. In this study, we conducted research to find out the information on the tectonic plate velocity changes in the Sunda Strait. We used Global Positioning System (GPS) time-series data provided by Indonesia Geospatial Information Agency (BIG). The time series data is used to calculate the earthquake displacement, the changes in GPS velocity of before and after earthquake, and the changes in velocity of each time interval. Our results show that the horizontal displacement due to the earthquake at all GPS stations ranged from 3.34 mm to 7.36 mm in the north-south direction and -27.45 mm to 0.18 mm in the east-west direction. Furthermore, the result of the changes in GPS velocity before and after an earthquake ranged from 2.25 mm/year to 12.60 mm/year and 1.80 mm/year to 13.35 mm/year. The pattern of change in velocity is likely due to post-seismic deformation from the 2012 Indian Ocean earthquake, the 2016 Sumatra earthquake, and also other tectonic factors.