GPS Campaigns Research Articles

Present-day crustal movement and seismic moment balance on major active faults around the easternmost segment of the Kunlun fault, Tibetan Plateau, China

After the 2021 Ms 7.4 Madoi, China earthquake located south of the eastern Kunlun fault, the coseismic Coulomb stress changes show that the earthquake potential is enhanced towards the easternmost segment of the Kunlun fault. Before the 2008 Mw 7.9 Wenchuan, China earthquake, the easternmost segment of the Kunlun fault is considered to being a region with the highest frequency occurrence of moderate-to-strong earthquakes in mainland China, where there are still at least three seismic gaps at present, indicating an urgent earthquake hazard. The tectonic deformation pattern is closely related to the development and occurrence of earthquakes. In this study, we collect all the available GPS data to obtain a crustal movement velocity field with high precision and high resolution by removing nontectonic effects within the study area. The GPS velocity profile and two-dimensional strain rates are then derived from the updated GPS velocities to analysis the characteristics of crustal deformation. Our results demonstrate that the Longriba fault zone slips predominantly right-laterally with the rate of 5.2 ± 0.5 mm/yr and the crustal shortening rate is ∼0.5 mm/yr across the Longriba and Longmenshan faults. Along with notable crustal extension and contraction, the principal strain rate field is distributed in a wide area on the northwest part of the Longmenshan fault, and decreases southwestward along the Longmenshan fault zone. In addition, we provide the time series of 8 campaign GPS stations which have never been published before. Moreover, the moment deficit estimate is a well-established way of assessing the earthquake hazard at a specific fault. Accompanying with the inverted slip rates and locking depth, we estimate the rates of moment accumulation on major faults and compare them with the seismic moment released on each fault derived from the Chinese historical earthquake catalog which extends for more than 2000 years in many regions. We find that the moment deficit is mainly concentrated on the Longriba fault with a value of 4.18 × 1017 Nm/yr. The Longriba fault have accumulated enough seismic energy to generate one Mw > 7.7 earthquake on it, or two Mw > 7.5 earthquakes on its two branches in the future. This study is an essential indicator for understanding the present-day tectonic deformation pattern in the Tibetan Plateau and is also helpful for seismic hazard assessment.

Present-day strain accumulations and fault kinematics at the Hatay Triple Junction using new geodetic constraints

The East Anatolian Fault (EAF), Cyprus Arc and Dead Sea Fault (DSF) intersect at the Hatay Triple Junction (HTJ) in southern Turkey, which is a tectonically controversial zone among researchers. Although it is not as active as the North Anatolian Fault (NAF) or other segments on the EAF in terms of seismicity, the HTJ accumulates strain causing considerable seismic activity in the region. Prior to this study, the strain accumulations and kinematics of the HTJ have not been precisely investigated using such a dense GPS network comprising permanent GPS stations, Turkish National Fundamental GPS Network (TUTGA) and campaign sites. Here, the fault slip rates and locking depths were constrained in the vicinity of HTJ using a new velocity field and improved block modeling. As per the results of block modeling, the EAF and Karatas-Osmaniye Fault (KOF) are fully locked down to depths of 15 km and 7 km, respectively. Furthermore, the Karasu Fault (KF) has a fully locked seismogenic zone to 7 km depth with a similar slip distribution to the EAF. Our kinematic model suggests 9.2 mm/yr left-lateral strike-slip rate and 2.0–2.7 mm/yr thrust faulting slip rate at the southwest end of the EAF. The KF appears to have left-lateral strike-slip at the rates ranging 4.0–5.5 mm/yr, while contrarily it has no significant normal/reverse faulting component. In addition, the KOF accommodates left-lateral strike-slip of 3.3–4.5 mm/yr and extension with the rates of 1.8–2.7 mm/yr. The new constraints on the fault slip rates associated with the HTJ correspond to predictions for a probable large earthquake with possible magnitude ranging from 7.2 to 7.6 for the EAF segment and 6.7–7.2 for the KF and KOF segments.

The vertical velocity field of the Tibetan Plateau and its surrounding areas derived from GPS and surface mass loading models

Obtaining a precise velocity field of the Earth's surface is critical for probing Earth's tectonic movements. In this contribution we construct a precise vertical velocity field with high-spatial resolution for the Tibetan Plateau (TP) and its surrounding areas using both 113 continuous and 969 campaign GPS time series over the period 2008 to 2019. Specifically, we compared the statistical distribution of residual continuous GPS time series to find the optimal regional surface mass loading (SML) models. The optimal modeled nontectonic displacements were used to correct these campaign GPS time series to reduce their scatter and accordingly improve the precision of the uplift rate estimates. The results showed that we could reduce the root mean square (RMS) on the vertical coordinate time series by more than 75% of the campaign GPS stations. We computed and removed vertical deformation due to horizontal strain rates obtained from GPS time series, and discussed dynamic sources (mantle dynamic topography, isostatic adjustment, and flexural loading) that drive the residual vertical tectonic motion. The study presents the most recent surface kinematic constraints for comprehending the dynamic sources of tectonic uplift or subsidence between and within tectonic units.Plain Language Summary: Movements of the Tibetan Plateau (TP) have a profound impact on adjacent areas. We collected all available GPS data to determine a precise vertical velocity field with high-spatial resolution. We make use of optimal surface mass loading (SML) models to improve estimation accuracy of campaign GPS stations, including an estimate of the vertical movement caused by the horizontal tectonic motions. We combine geological and geophysical data with our vertical velocity field to understand the dynamic sources of uplift or subsidence between and within tectonic units of the TP.

Monitoring Land Subsidence and its Effect on Surabaya Coastal Inundation by Utilizing GPS Campaigns Data

Land subsidence is a process of land movement based on a certain datum (geodetic reference frame) in which there are various variables causing it. This phenomenon occurs in many big cities in Indonesia, which is the city of Surabaya. The Surabaya city has a type of soil in the form of alluvial soil which is prone to movement. The accumulation of land subsidence that occurs will certainly cause its own losses. As a result, it can damage urban infrastructure so that in the future it can cause disruption to the environment, economic activities, and social life in the region. In addition, the Surabaya area is also a coastal area. Coastal areas have characteristics where this area will be strongly influenced by natural events. One of the natural events that affect the oceans and coastal areas is global temperature changes. The phenomenon of global temperature changes can affect sea level rise. If sea level rise occurs accompanied by an increase in the rate of land subsidence, this can result in flooding or inundation in coastal areas. Considering that the city of Surabaya is a metropolitan city that has a high population density and a continuous level of development, mitigation efforts are important in following up on land subsidence in this area. One of the efforts that can be applied is by conducting GPS observations. The outcomes of the GPS observations were then processed using scientific software in the form of GAMIT/GLOBK. According to the study’s findings indicated that Surabaya is experiencing land subsidence in the northern and eastern coastal areas with a range of 0.2 – 83.3 mm/year. The point that experienced a significant decline was in the border area of Tandes and Asemrowo, namely station BM35. Furthermore, land subsidence conditions influence the extent of tidal inundation, where in 2032 tidal inundation will inundate 105.411 km2.

Historical development of SIRGAS

Abstract The Geodetic Reference System for the Americas (Sistema de Referencia Geodésico para las Américas, SIRGAS) was initiated in 1993 for South America at an international conference organised by the International Association of Geodesy (IAG), the Pan-American Institute for Geography and History (PAIGH), the Deutsches Geodätisches Forschungsinstitut (DGFI), and the U.S. Defense Mapping Agency (DMA) in Asunción, Paraguay. The corresponding South American reference network was observed in 1995 by a ten-day GPS campaign at 58 stations. The network was extended to Central and North America in 2000 and immediately afterwards converted to a frame of continuously observing GNSS stations instead of short-term campaigns. The linear station position changes (velocities) were estimated by a multi-year least squares adjustment of weekly solutions, the first being published in 2002. The total set of station velocities served for the computation of continuous surface deformation models, the first over South America was published in 2005. Today, SIRGAS is accepted by most of the American states as the official geodetic reference frame. Besides the product generation (station positions, velocities, and surface deformation), SIRGAS is active in education and training offering schools and workshops for students, surveyors, and other stakeholders.

Geodetic observation of strain accumulation in the Banda Arc region

The Banda Arc region has produced several large destructive earthquakes, some of which have been followed by tsunamis. To better understand the earthquake potential in this area, we performed a comparison between geodetic and seismic moment rates. Data were collected from 110 continuous and campaign GPS stations observed for approximately ten years. The results show that the derived velocity field indicates that the Banda Arc deformation is characterized mainly by crustal shortening caused by the interaction of the Australian, Pacific, and Philippine Sea plates. Meanwhile, the contraction strain pattern dominates the Banda Arc area except around Papuan Bird’s Head. Areas with high strain rates have a history of significant seismicity, such as the Flores-Wetar Back Arc, the area around Ambon, and the Papuan Bird’s Head. The ratio of the geodetic moment rate to the seismic moment rate in the Banda, Bird’s Head, South Sulawesi, and Sumba zones are ∼1.5–7.0, indicating a moment deficit rate. The moment deficit rate provides an equivalent earthquake potential of Mw 7.7–8.1. This potential may be related to an aseismic deformation or stress accumulation, the under-sampling of long-term earthquake rates within the seismic catalogs, or a composite of these factors.

A new approach considering temporal correlations for GPS campaign time series

GPS campaign-mode surveys are periodically collected measurements and their time series has a considerable percentage of data gaps unlike continuous time series. Studying error characteristics of a time series is imperative to compute reliable parameter uncertainties. The power-law process can best describe the background noise for a GPS continuous time series and may be introduced into the analysis through well-known methods. However, the power-law process cannot be applied successfully over GPS campaign time series due to the constraints mentioned above. Here we demonstrate a new approach enabling one to project the stochastic properties of campaign time series into the stochastic domain of the permanent stations of International GNSS Service (IGS) network. The stochastic domain, the combination of white noise (WN) and flicker noise (FN), was obtained from the power spectrum of a continuous time series consisting of truncated daily RINEX observations. We implemented it in the Python3 environment as an open-source package called GPS/GNSS campaign time series analysis (GCTS v1.0). The analysis showed that the velocity uncertainties may be, on average, underestimated by a factor of 2 when assuming the WN-only noise model using campaign data from the UNAVCO data archive collected in San Bernardino and its vicinity. Moreover, to reveal the progress of the new approach, we modelled buried screw dislocations of the San Jacinto, the San Andreas, and parallel faults in their vicinity in elastic half-space. When using the new approach with the combination of WN and FN instead of the WN-only model, we achieved a significant improvement of 15% on average in the chi-square value. Our outcomes showed that the noise process should be considered even for campaign time series. The proposed approach facilitates the analysis of GPS campaign time series even if they include considerable data gaps.

Analysis of local surface displacement using repeated GPS measurements: a case study of the Guabirotuba area, Curitiba, Brazil

In recent years, the ability of GNSS systems to estimate high accuracy 3D positions has greatly contributed to the development of new monitoring techniques aimed at understanding the mechanisms by which the different Earth processes are generated. This paper presents the result of 9 GPS campaigns, between 2014 and 2019 for a group of 29 stations, held in the Guabirotuba urban area, Curitiba, Brazil, intending to estimate local crustal movements. The average magnitude and direction of horizontal velocities obtained for each site, allow demonstrating deformation of the southern zone of the area as a result of a local landslide process. The magnitude of the vectors varies between 1 and 16 mm/a horizontally. All sites had an absolute vertical movement, probably correlated with a local geological pattern or a physical site’s motion driven by environmental mass redistribution. The uncertainties in positions and velocities for a long-term survey (over 5 years), showed good consistency at most sites when compared with the coordinates and velocities precision of the latest SIRGAS solution. The typical precision for the station positions at the reference epoch was ±2 mm horizontally and ±5 mm vertically, and ±0.60 mm/a horizontally and ±1.37 mm/a vertically for the constant velocities.

GEODETIC SLIP RATE ESTIMATES FOR THE KUMERING AND SEMANGKO SEGMENTS OF THE SUMATERA FAULT

<p>The Sumatran fault is a right lateral active inland fault in southern Sumatra, Indonesia. Although historical earthquake records have shown that magnitude 7 class earthquakes have occurred during the last century, the slip rates along the Sumatran fault have not been studied in detail. This is the first research using a new dense GPS array, in which stations are orthogonal to the fault, to analyze the fault slip rates along the Kumering and Semangko segments in southern Sumatra. In this study, we process GPS data from 14 campaign and continuous GPS points. The results show velocities of 14 mm/yr and 15 mm/yr for these two fault segments, respectively. Our estimated geodetic slip rate suggests that the Sumatran fault has a relatively homogeneous slip rate from southern to northern Sumatra.</p>

Results of land subsidence measurement using GPS method in the Jakarta groundwater basin in 2015-2019

The development of population and development activities in big cities in Indonesia, especially in the city of Jakarta and surrounding areas is very rapid. From several land subsidence studies, several factors have been identified that cause land subsidence, namely: excessive groundwater extraction, reduction due to building/infrastructure loads, subsidence due to natural consolidation of soft soil layers, and subsidence due to tectonic forces. At present the exploitation of ground water for industrial and residential needs is at a level that needs attention. Excessive pumping of groundwater will cause a decrease in the quantity of ground water, entry of seawater into the land (sea water intrusion) and land subsidence. Symptoms of the negative impact of land subsidence have been felt in several areas, especially in industrial areas located in the northern part of Jakarta. This land subsidence can be measured by GPS or satellite geodetic method, which have begun to develop in Indonesia in the past two decades. Measurements were made using the radial method at 53 GPS points in 2015 up to 100 measurement points in 2019 in Jakarta Groundwater Basin. The result of these campaign GPS surveys that is northern part of Jakarta relatively had higher subsidence rate than the southern. The largest subsidence almost reached 6.2 cm/year in Muara Baru in northern area which is southern area only suffered an average rate of 1.16 cm/year.

New geodetic constraints on southern San Andreas fault-slip rates, San Gorgonio Pass, California

AbstractAssessing fault-slip rates in diffuse plate boundary systems such as the San Andreas fault in southern California is critical both to characterize seismic hazards and to understand how different fault strands work together to accommodate plate boundary motion. In places such as San Gorgonio Pass, the geometric complexity of numerous fault strands interacting in a small area adds an extra obstacle to understanding the rupture potential and behavior of each individual fault. To better understand partitioning of fault-slip rates in this region, we build a new set of elastic fault-block models that test 16 different model fault geometries for the area. These models build on previous studies by incorporating updated campaign GPS measurements from the San Bernardino Mountains and Eastern Transverse Ranges into a newly calculated GPS velocity field that has been removed of long- and short-term postseismic displacements from 12 past large-magnitude earthquakes to estimate model fault-slip rates. Using this postseismic-reduced GPS velocity field produces a best-fitting model geometry that resolves the long-standing geologic-geodetic slip-rate discrepancy in the Eastern California shear zone when off-fault deformation is taken into account, yielding a summed slip rate of 7.2 ± 2.8 mm/yr. Our models indicate that two active strands of the San Andreas system in San Gorgonio Pass are needed to produce sufficiently low geodetic dextral slip rates to match geologic observations. Lastly, results suggest that postseismic deformation may have more of a role to play in affecting the loading of faults in southern California than previously thought.

Mechanical Implications of Creep and Partial Coupling on the World's Fastest Slipping Low‐Angle Normal Fault in Southeastern Papua New Guinea

AbstractWe use densely spaced campaign GPS observations and laboratory friction experiments on fault rocks from one of the world's most rapidly slipping low‐angle normal faults, the Mai'iu fault in Papua New Guinea, to investigate the nature of interseismic deformation on active low‐angle normal faults. GPS velocities reveal 8.3 ± 1.2 mm/year of horizontal extension across the Mai'iu fault, and are fit well by dislocation models with shallow fault locking (above 2 km depth), or by deeper locking (from ~5–16 km depth) together with shallower creep. Laboratory friction experiments show that gouges from the shallowest portion of the fault zone are predominantly weak and velocity‐strengthening, while fault rocks deformed at greater depths are stronger and velocity‐weakening. Evaluating the geodetic and friction results together with geophysical and microstructural evidence for mixed‐mode seismic and aseismic slip at depth, we find that the Mai'iu fault is most likely strongly locked at depths of ~5–16 km and creeping updip and downdip of this region. Our results suggest that the Mai'iu fault and other active low‐angle normal faults can slip in large (Mw > 7) earthquakes despite near‐surface interseismic creep on frictionally stable clay‐rich gouges.

Current State of Crustal Deformation and Seismic Activity from Seismic and Geodetic Data in Aswan Region, Egypt

Aswan region is a very important region for Egypt where the High Dam is situated. The wellbeing of the dam and its encompassing region is of extreme worry to all the Egyptian separate networks. Hence, a seismic network was introduced to screen the earthquake action consistently. Several systems of local and sub-regional geodetic networks have been established around the active faults to monitor the crustal deformation associated with the earthquake activity. Seismic information utilized in this exploration was recorded from Aswan Seismic Network from 1982 to 2015. The events are gathered in Kalabsha region where there is a crossing point of the east and west Kalabsha faults. The earthquakes epicenters are appropriated in two seismic zones, shallow and deep. Shallow occasions have central profundities of under 10 km while deep occasions stretch out from 10 to 30 km. Connection between the seismicity and the water level variety at Lake Nasser gives extraordinary proposal to recognize the small scale earthquakes, especially, those in shallow seismic zone. Eleven benchmarks of a sub-local GPS network were set up to investigation the current crustal distortion. A few battles of GPS estimations were completed somewhere in the range of 1996 and 2015. An early indication for the rate of gathering energy stress on the faults and thus the probability of the occurrence of earthquakes can be observed from the monitoring of the repeated last 11-years GPS campaigns from 2004 to 2015. The outcomes uncovered that the local and neighborhood even developments are at the dimension from ((20 to 28 (±1.5)) and ((2 to 4 (±0.5)) mm/an individually. There are compression and tension components seen from the evaluated strain tensors. The P-and T-tomahawks got from earthquake shortcoming plane arrangements are steady with these segments. This examination centers around the present condition of the seismicity and crustal deformation in Aswan area.

Crustal deformation analysis across Garhwal Himalaya: Part of western Himalaya using GPS observations

Past earthquakes in the Himalayas are mainly due to tectonic activities along the thrust faults parallel to the Himalayan belt. In order to study the ongoing tectonic process, crustal deformation at a selected transect in a part of western Himalayas as well as of the Indian plate, then: are studied by the analyses of GPS data processed in a GAMIT/GLOBK platform. The data were collected from four local continuous operating reference stations (CORS), six International Global Navigation Satellite System Service (IGS) stations and five surveyed based GPS campaign stations transverse to major faults system. Results show an annual crustal motion of 19.18 mm Near Southern Tibetan Detachment (STD), 18.72 mm near Main Central Thrust (MCT), 11.93 mm near Main Boundary Thrust (MBT) and 11.53 mm near Himalayan Frontal Thrust (HFT) in India fixed reference. The present day Indian plate motion was estimated to be 55.33 mm/yr. In the study region at western Himalaya, crustal convergence of 13.83 mm/yr was observed in Dehradun-Badrinath sector in Uttarkhand. GPS sites near to north of HFT shows a westward movements and sites at peninsular India shows eastward movements suggesting possible counter clockwise rotation of the Indian plate. The annual motion across HFT varies between 0.1 and 2.0 mm, suggesting that HFT is locked in Garhwal region of western Himalaya. Insignificant movement across HFT indicates greater strain accumulation and the possibility of earthquakes in near future. The study suggests requirement of continuous monitoring of deformation across major thrusts in the Himalaya with dense network of GPS stations.

Model Sesar Pati di Jawa Tengah Berdasarkan Data GPS

The campaign GPS survey was conducted in the 2017 - 208 by Centre for Volcanology and Geological Hazard Mitigation, Geological Agency for the purpose of studying the caracteristic of the Pati Fault. The complete processing and analysis of the GPS observations were performed using Gamit/Globk software version 10.6. Horizontally, displacement of GPS stations generally to the southwest and to the south with a velocity of 3.04 mm/yr up to 19.49 mm/yr. While the vertical displacement up and down with values varying from -125.60 mm/yr to 4.07 mm/yr. Base on displacement pattern of GPS stations by using Coulomb 3.3 softwaere, a Pati Fault model consist of three segments that have potensial produce earthquakes with moment magnitude Mw 6.2, Mw 6.2, and Mw 6.4 respectively.Keywords: GPS survey, Pati Fault, displacement, fault model.

Surface deformation and earthquake potential in Surabaya from GPS campaigns data

Study by the National Centre for Earthquake Studies suggests the presence of two segments of Kendeng active fault, namely Surabaya fault and Waru fault in Surabaya. This study aims to investigate the surface deformation and earthquake potential in Surabaya that possibly related to the activities of those two faults. We use GPS campaigns data conducted in March 2017, September 2017, May 2018, and October 2018 and five GGPS CORS stations around Surabaya provided by the Indonesian Geospatial Information Agency. In total, 21 GPS stations data were processed to obtain horizontal and vertical displacement velocities in each station. The results showed almost all stations move toward southeast with the velocity rates range from 1.034 cm/yr to 5.674 cm/yr, except BM33 and SB07 that moves northeast with the velocity rates 4.065 cm/yr and 3.312 cm/yr respectively. For the vertical displacements, almost all stations subject to subsidence with the rates range from -0.190 cm/yr to -5.769 cm/yr. Only three stations subject to uplift namely BM23 with the rate of 0.234 cm/yr, BM24 with the rate of 2.844 cm/yr, and BM29 with the rate of 3.33 cm/yr. The strain analyses showed large shortenings in the area between two faults with the values up to 11.95 μstrain. From the results, we can conclude that the surrounding area of the two faults have different deformation patterns, and by confirming with geological data, we suggest that Surabaya has an earthquake potential due to the active faults.

Accuracy of Deformation Rates from Campaign GPS Surveys Considering Extended Observation Session and Antenna Set-Up Errors

GPS campaign measurements are still in use in the monitoring of ground deformation. Campaign measurements are frequently referred to because installing permanent stations are costly, and they cannot be installed at the desired density. Using the data from the International Global Navigation Satellite Systems (GNSS) Service (IGS) permanent GPS stations, the duration, sampling interval, etc. of the campaign measurements can be simulated. Thus, the contribution of the campaign data to the monitoring of the ground deformation can be evaluated. In this study, we carried out an experiment with the aim of determining the deformation of tectonic plates at the selected IGS stations more accurately considering by extending the observation duration to a full 24 h length. We also made an attempt to take into consideration the antenna set up errors developing a scenario referring to the information available in the literature. We have decimated the continuous data of 40 globally scattered IGS stations into monthly intervals between 2012 and 2016 and estimated the deformation rates at the IGS stations from a continuous time series of four years. The continuous time series solutions for those stations were produced by the Jet Propulsion Laboratory (JPL), NASA. We compare velocities (i.e., the deformation rates) determined from GPS campaigns (in which the sampling was performed monthly and four-monthly) with those of the continuous data. The major conclusion of this study is that the vertical velocity estimation accuracy of the GPS campaign measurements had been improved by about 85% by extending the session duration to 24 h. The repetition interval of GPS campaign measurements as per one observation every four months produced only slightly coarser accuracy (i.e., on the average 8% poorer) than those of the measurements repeated once every month.

Assessment of geodetic velocities using GPS campaign measurements over long baseline lengths

Abstract. GPS campaign measurements are frequently used in order to determine geophysical phenomena such as tectonic motion, fault zones, landslides, and volcanoes. When observation duration is shorter, the accuracy of coordinates are degraded and the accuracy of point velocities are affected. The accuracies of the geodetic site velocities from a global network of International GNSS Service (IGS) stations were previously investigated using only PPP. In this study, we extend which site velocities will also be assessed, including fundamental relative positioning. PPP-derived results will also be evaluated to see the effect of reprocessed JPL products, single-receiver ambiguity resolution, repeating survey campaigns minimum 3 days at the site, and eliminating noisier solutions prior to the year 2000. To create synthetic GPS campaigns, 18 globally distributed, continuously operating IGS stations were chosen. GPS data were processed comparatively using GAMIT/GLOBK v10.6 and GIPSY-OASIS II v6.3. The data of synthetic campaign GPS time series were processed using a regression model accounting for the linear and seasonal variation of the ground motion. Once the velocities derived from 24 h sessions were accepted as the truth, the results from sub-sessions were compared with the results of 24 h and hypothesis testing was applied for the significance of the differences. The major outcome of this study is that on global scales (i.e. over long distances) with short observation sessions, the fundamental relative positioning produces results similar to PPP. The reliability of the velocity estimation for GPS horizontal baseline components has now been improved to about 85 % of the average for observation durations of 12 h.

Contemporary crustal tectonic movement in the southern Sichuan-Yunnan block based on dense GPS observation data

We analyzed 360 permanent and campaign GPS data from 1999 to 2017 in the southern Sichuan-Yunan block, and obtained crustal horizontal deformation in this region. Then, we derived the strain rate using a multi-scale spherical wavelet method. Results reveal a complex pattern of tectonic movement in the southern Sichuan-Yunnan block. Compared to the stable Eurasian plate, the maximum rate of the horizontal deformation in the southern Sichuan-Yunnan block is approximately 22 mm/a. The Xiaojiang fault shows a significantly lower deformation—a left-lateral strike-slip movement of 9.5 mm/a. The Honghe fault clearly shows a complex segmental deformation from the north to south. The northern Honghe fault shows 4.3 mm/a right strike-slip with 6.7 mm/a extension; the southern Honghe fault shows 1.9 mm/a right strike-slip with 1.9 mm/a extension; the junction zone in the Honghe and Lijiang–Xiaojinhe faults shows an obvious clockwise-rotation deformation. The strain calculation results reveal that the maximum shear-strain rate in this region reaches 70 nstrain/a, concentrated around the Xiaojiang fault and at the junction of the Honghe and Lijiang–Xiaojinhe faults. We note that most of the earthquakes with magnitudes of 4 and above that occurred in this region were within the high shear strain-rate zones and the strain rate gradient boundary zone, which indicates that the magnitude of strain accumulation is closely related to the seismic activities. Comparison of the fast shear-wave polarization direction of the upper-crust with the upper-mantle anisotropy and the direction of the surface principal compressive strain rate obtained from the inversion of the GPS data reveals that the direction of the surface principal compressive strain is basically consistent with the fast shear-wave polarization direction of the upper crust anisotropy, but different from the polarization direction of the upper mantle. Our results support the hypothesis that the principal elements of the deformation mechanism in the southern Sichuan-Yunnan block are decoupling between the upper and lower crust and ductile flow in the lower crust.

Interseismic Ground Deformation and Fault Slip Rates in the Greater San Francisco Bay Area From Two Decades of Space Geodetic Data

AbstractThe detailed spatial variations of strain accumulation and creep on major faults in the northern San Francisco Bay Area (North Bay), which are important for seismic potential and evaluation of natural hazards, remain poorly understood. Here we combine interferometric synthetic aperture radar data from the ERS‐1/2 and Envisat satellites between 1992 and 2010 with continuous and campaign GPS data to obtain a high spatial and temporal coverage of ground deformation of the North Bay. The SAR data from both ascending and descending orbits are combined to separate horizontal and vertical components of the deformation. We jointly invert the horizontal component of the mean velocities derived from these data to infer the deep strike‐slip rates on major locked faults. We use the estimated deep rates to simulate the long‐wavelength deformation due to interseismic elastic strain accumulation along these locked faults. After removing the long‐wavelength signal from the InSAR horizontal mean velocity field, we estimate fault‐parallel surface creep rates of up to 2 mm/year along the central section of the Rodgers Creek fault and surface creep rates ranging between 2 and 4 mm/year along the Concord fault. No surface creep is geodetically resolved along the West Napa and Green Valley fault zones. We identified characteristically repeating earthquakes on the Rodgers Creek fault, the West Napa fault, the Green Valley fault, and the Concord fault. Nontectonic deformation in the Geysers geothermal field and in Late Cenozoic basins (Rohnert Park and Sonoma basins) are also observed, likely due to hydrological and sediment‐compaction processes, respectively.