Crustal Deformation Rates Research Articles

Calibrated Absolute Seafloor Pressure Measurements for Geodesy in Cascadia

AbstractThe boundary between the overriding and subducting plates is locked along some portions of the Cascadia subduction zone. The extent and location of locking affects the potential size and frequency of great earthquakes in the region. Because much of the boundary is offshore, measurements on land are incapable of completely defining a locked zone in the up‐dip region. Deformation models indicate that a record of seafloor height changes on the accretionary prism can reveal the extent of locking. To detect such changes, we have initiated a series of calibrated pressure measurements using an absolute self‐calibrating pressure recorder. A piston‐gauge calibrator under careful metrological considerations produces an absolutely known reference pressure to correct seafloor pressure observations to an absolute value. We report an accuracy of about 25 ppm of the water depth, or 0.02 kPa (0.2 cm equivalent) at 100 m to 0.8 kPa (8 cm equivalent) at 3,000 m. These campaign survey‐style absolute pressure measurements on seven offshore benchmarks in a line extending 100 km westward from Newport, Oregon from 2014 to 2017 establish a long‐term, sensor‐independent time series that can, over decades, reveal the extent of vertical deformation and thus the extent of plate locking and place initial limits on rates of subsidence or uplift. Continued surveys spanning years could serve as calibration values for co‐located or nearby continuous pressure records and provide useful information on possible crustal deformation rates, while epoch measurements spanning decades would provide further limits and additional insights on deformation.

Revealing Crustal Deformation and Strain Rate in Taiwan Using InSAR and GNSS

AbstractInterseismic deformation describes the gradual accumulation of crustal strain within the tectonic plate and along the plate boundaries before the sudden release as earthquakes. In this study, we use 5 years of high spatial and temporal geodetic measurements, including Global Navigation Satellite System and Interferometric Synthetic Aperture Radar to monitor 3‐dimension interseismic crustal deformation and horizontal strain rate in Taiwan. We find significant deformation (strain rate >8 10−6 yr−1) along the plate boundary between the Philippine Sea and the Eurasian Plates in east Taiwan. The high strain rate in the southern part of the Western Foothills is distributed along a few major fault systems, which reveals the geometry of the deformation front in west Taiwan. Our results help identify active faults in southwest and north Taiwan that were not identified before. These findings can be insightful in informing future seismic hazard models.

Refining Rates of Active Crustal Deformation in the Upper Plate of Subduction Zones, Implied by Geological and Geodetic Data: The E-Dipping West Crati Fault, Southern Italy

We investigate crustal deformation within the upper plate of the Ionian Subduction Zone (ISZ) at different time scales by (i) refining geodetic rates of crustal extension from continuous Global Navigation Satellite System (GNSS) measurements and (ii) mapping sequence of Late Quaternary raised marine terraces tectonically deformed by the West Crati normal fault, in northern Calabria. This region experienced damaging earthquakes in 1184 (M 6.75) and 1854 (M 6.3), possibly on the E-dipping West Crati fault (WCF) which, however, is not unanimously considered to be a seismogenic source. We report geodetic measurements of extension and strain rates across the strike of the E-dipping WCF and throughout the northern Calabria obtained by using velocities from 18 permanent GNSS stations with a series length longer than 4.5 years. These results suggest that crustal extension may be seismically accommodated in this region by a few normal faults. Furthermore, by applying a synchronous correlation approach, we refine the chronology of understudied tectonically deformed palaeoshorelines mapped on the footwall and along the strike of the WCF, facilitating calculation of the associated fault-controlled uplift rates. Raised Late Quaternary palaeoshorelines are preserved on the footwall of the WCF indicating that “regional” uplift, likely related to the deformation associated either with the subduction or mantle upwelling processes, is affected by local footwall uplift. We show that GIS-based elevations of Late Quaternary palaeoshorelines, as well as temporally constant uplift rates, vary along the strike of the WCF, implying normal faulting activity through time. This suggests that (i) the fault slip rate governing seismic hazard has also been constant over the Late Quaternary, over multiple earthquake cycles, and (ii) our geodetically derived fault throw rate for the WCF is likely a more than reasonable value to be used over longer time scales for an improved seismic hazard assessment. Overall, we emphasize the importance of mapping crustal deformation within the upper plate above subduction zones to avoid unreliable interpretations relating to the mechanism controlling regional uplift.

Revealing crustal deformation and strain rate in Taiwan using InSAR and GNSS

Revealing crustal deformation and strain rate in Taiwan using InSAR and GNSS

Present-day crustal deformation and slip rate along the southern Sagaing fault in Myanmar by GNSS observation

The Sagaing fault in Myanmar runs through the entire country and is responsible for major earthquakes, yet only its northern half has been studied geodetically to date. We analyzed Global Navigation Satellite System (GNSS) data to estimate crustal deformation along the central and southern parts of the Sagaing fault. We used a 2-dimensional dislocation model to estimate slip rate, locking depth and lateral offset between surface fault trace and downdip edge of the locked fault along the Sagaing (SGs), Meiktila (MTLs) and Bago (BGOs) segments of the fault. The estimated slip rate is 16–24 mm/yr with a locking depth of 10–16 km in our analysis for the central to southern segments, which is deeper than the locking depth of northern segment from previous studies. The slip rate is ~23–24 mm/yr in the central part of the Sagaing fault, while it is probably slower (~16 mm/yr) in the southern part of our study area. The predicted maximum shear strain from the optimal model is shifted from the surface fault trace. If the locked part of the fault connects directly from the deeper offset dislocation to the surface fault trace, it may be dipping with inferred values of 71°E for the SGs and 78°W for the MTLs, based on the distance between surface trace and the dislocation line at depth. The estimated potential magnitude of earthquakes for each segment as of 2021 are Mw ~7.3 in SGs, Mw ~7.4 in MTLs and Mw ~7.3 in BGOs, respectively.

Crustal deformation detection capability of the GNSS-A seafloor geodetic observation array (SGO-A), provided by Japan Coast Guard

The GNSS-A technique is an observation method that can detect seafloor crustal deformations with centimeter-level positioning accuracy. The GNSS-A seafloor geodetic observation array operated by the Japan Coast Guard (SGO-A) has been constructed near the Japanese Islands along the Nankai Trough and the Japan Trench. This observation array has detected several earthquakes’ displacements and episodic slow crustal deformation. To compare the detection results of SGO-A with other observation networks and expand the SGO-A coverage area, it is necessary to correctly understand its detection capability. In this paper, numerical simulations and statistical verifications were used to assess the capabilities of the present GNSS-A system using a manned vessel (observation frequency: 4–6 times/year, positioning accuracy: standard deviation = 1.5 cm) to detect (1) secular deformation only, (2) a transient slip event only and (3) secular deformation and a transient event together. We verified these results with appropriate thresholds and found the following features: When it is known that there is no transient event, the 95% confidence level (CL) for the estimation of secular crustal deformation rate with 4-year observation is about 0.5–0.8 cm/year; when the deformation rate is known, a signal of about 3.0 cm can be detected by observations of about 4 times before and after the transient event. When the deformation rate and the transient event are detected together, to keep the false positive low (about 0.05), the false negative becomes high (about 0.7–0.2 for detecting a signal of 4.5–6.0 cm). The determined rate and event variations are approximately 1.8 cm/year (95%CL) and 1.5 cm (standard deviation), respectively. We also examined the detection capability for higher observation frequency and positioning accuracy, to examine how the detection capability improves by technological advancements in the future. Additionally, we calculated the spatial range of event detectability using the determined values of detection sensitivity. Obtained results show that each seafloor site can detect a slip event of < 1.0 m scale within about 30 km radius, and approximately one-third of the subseafloor slip event over 100 km from land along the Nankai Trough can only be detected by SGO-A.

Crustal deformation, active tectonics and seismic potential in the Sicily Channel (Central Mediterranean), along the Nubia\u2013Eurasia plate boundary

Based on multidisciplinary data, including seismological and geodetic observations, as well as seismic reflection profiles and gravity maps, we analysed the pattern of crustal deformation and active tectonics in the Sicily Channel, a key observation point to unravel the complex interaction between two major plates, Nubia and Eurasia, in the Mediterranean Sea. Our data highlight the presence of an active ~ 220-km-long complex lithospheric fault system (here named the Lampedusa-Sciacca Shear Zone), approximately oriented N–S, crossing the study area with left-lateral strike-slip deformations, active volcanism and high heat flow. We suggest that this shear zone represents the most active tectonic domain in the area, while the NW–SE elongated rifting pattern, considered the first order tectonic feature, appears currently inactive and sealed by undeformed recent (Lower Pleistocene?) deposits. Estimates of seismological and geodetic moment-rates, 6.58 × 1015 Nm/year and 7.24 × 1017 Nm/year, respectively, suggests that seismicity accounts only for ~ 0.9% of crustal deformation, while the anomalous thermal state and the low thickness of the crust would significantly inhibit frictional sliding in favour of creeping and aseismic deformation. We therefore conclude that a significant amount of the estimated crustal deformation-rate occurs aseismically, opening new scenarios for seismic risk assessments in the region.

Crustal deformation rates in Kashmir valley and adjoining regions from continuous GPS measurements from 2008 to 2019

We present GPS velocities in Kashmir valley and adjoining regions from continuous Global Positioning System (cGPS) network during 2008 to 2019. Results indicate total arc normal shortening rates of ~ 14 mm/year across this transect of Himalaya that is comparable to the rates of ~ 10 to 20 mm/year reported else-where in the 2500 km Himalaya Arc. For the first time in Himalayas, arc-parallel extension rate of ~ 7 mm/year was recorded in the Kashmir valley, pointing to oblique deformation. Inverse modeling of the contemporary deformation rates in Kashmir valley indicate oblique slip of ~ 16 mm/year along the decollement with locking depth of ~ 15 km and width of ~ 145 km. This result is consistent with the recorded micro-seismicity and low velocity layer at a depth of 12 to 16 km beneath the Kashmir valley obtained from collocated broadband seismic network. Geodetic strain rates are consistent with the dislocation model and micro-seismic activity, with high strain accumulation (~ 7e−08 maximum compression) to the north of Kashmir valley and south of Zanskar ranges. Assuming the stored energy was fully released during 1555 earthquake, high geodetic strain rate since then and observed micro-seismicity point to probable future large earthquakes of Mw ~ 7.7 in Kashmir seismic gap.

Viscous Effects in the Solid Earth Response to Modern Antarctic Ice Mass Flux: Implications for Geodetic Studies of WAIS Stability in a Warming World

AbstractThe West Antarctic Ice Sheet (WAIS) overlies a thin, variable-thickness lithosphere and a shallow upper-mantle region of laterally varying and, in some regions, very low (~1018 Pa s) viscosity. We explore the extent to which viscous effects may affect predictions of present-day geoid and crustal deformation rates resulting from Antarctic ice mass flux over the last quarter century and project these calculations into the next half century, using viscoelastic Earth models of varying complexity. Peak deformation rates at the end of a 25-yr simulation predicted with an elastic model underestimate analogous predictions that are based on a 3D viscoelastic Earth model (with minimum viscosity below West Antarctica of 1018 Pa s) by ~15 and ~3 mm yr−1 in the vertical and horizontal directions, respectively, at sites overlying low-viscosity mantle and close to high rates of ice mass flux. The discrepancy in uplift rate can be reduced by adopting 1D Earth models tuned to the regional average viscosity profile beneath West Antarctica. In the case of horizontal crustal rates, adopting 1D regional viscosity models is no more accurate in recovering predictions that are based on 3D viscosity models than calculations that assume a purely elastic Earth. The magnitude and relative contribution of viscous relaxation to crustal deformation rates will likely increase significantly in the next several decades, and the adoption of 3D viscoelastic Earth models in analyses of geodetic datasets [e.g., Global Navigation Satellite System (GNSS); Gravity Recovery and Climate Experiment (GRACE)] will be required to accurately estimate the magnitude of Antarctic modern ice mass flux in the progressively warming world.

Estimate of the contraction rate of central Japan through the deformation of the Philippine Sea slab

The Philippine Sea (PHS) slab is severely deformed beneath central Japan, but it is subject to little deformation before the subduction along the Nankai Trough. Thus, it is considered that the currently observed deformation of the PHS slab has been formed only after the subduction along the Nankai Trough. This study estimates the contraction rate of the PHS slab along segments roughly parallel to the Nankai Trough, assuming that the configuration of the PHS slab is stationary in time in the coordinate system fixed to the overriding plate. Results show that the contraction rate is small beneath most parts of Shikoku (≤ 0.3 mm/year) and the offshore fore-arc (≤ 0.6 mm/year), while it increases from the Pacific coastal region (3–6 mm/year) to the inland region (approximately 20 mm/year) beneath central Japan. Considering various error sources, the strain rate is estimated to be about 4–7 × 10−8/year beneath the inland region of central Japan, although it could be reduced by about 20% if the PHS slab has a tear beneath the Kii Strait. Due to the geographical concordance of the deformation between the PHS slab and the upper crust above the slab, the contraction rate of the PHS slab could be used as a proxy to provide an independent estimate of the crustal deformation rate of central Japan over the long term, which is slower than the geodetic estimate while faster than the geologic one.ᅟ

Incremental Emplacement of the Late Jurassic Midcrustal, Lopolith‐Like Qitianling Pluton, South China, Revealed by AMS and Bouguer Gravity Data

AbstractModes of magma emplacement may provide key information on geodynamic‐tectonic settings of magmatism, when the threshold of magma volume and duration of emplacement process is crossed, brittle/ductile crustal deformation behavior, and volumes and rates of magma transfer in the crust. The majority of upper‐crustal granitic intrusions are incrementally emplaced as laccoliths or sills, while midcrustal or deeper‐level granitic intrusions appear to be predominantly emplaced as sills or lopoliths, but relatively few examples have been studied. We present a case study on the Jurassic Qitianling pluton from South China, which was constructed in the upper part of the middle crust (at a depth of ~10–15 km). To characterize its emplacement mechanism and evolution, we have combined field and microscopic observations, Anisotropy of Magnetic Susceptibility measurements and Bouguer gravity anomaly modeling. The main findings are (1) the generally undeformed granite‐country rock contacts with a narrow thermal aureole, (2) irregularly wavy and gradational contacts between the main granite facies, (3) dominant subhorizontal magnetic fabrics in the granites with a scattered magnetic foliation, (4) rare occurrence of dykes, and (5) a subcircular surface and lopolith‐like pluton geometry. Accordingly, we suggest that the Qitianling pluton forms an ~25‐km wide and ~5‐km thick lopolith that was incrementally emplaced during a period of tectonic quiescence, most likely by under‐accretion of multiple magma sheets deflected from magma pulses that ascended through pipe‐like channels. The mineralogical and compositional variation of the pluton may be the result of in situ fractionation, fractionation at deeper crustal level, or variation in source‐derived melt compositions.

Seismic hazard assessment of the central North Anatolian Fault (Turkey) from GPS-derived strain rates and b-values

ABSTRACTThe North Anatolian Fault (NAF) represents one of the most seismically active transform zones on Earth. It is characterized by high rates of crustal deformation that generate destructive earthquakes. These rates are induced by convergence of the northward-migrating Arabian and African plates with respect to the stable Eurasian plate. Therefore, the NAF represents a natural earthquake laboratory with a wide range of earthquake sizes (M ≤ 7.9) to investigate by using interdisciplinary approaches (seismological, magnetism, geological, gravitational, and geodetic studies). In this study, we compare the results of an analysis of b-values from seismicity and GPS (Global Positioning System) measurements of the strain rate to understand their coupling in terms of faulting and earthquake hazard implications. In particular, this comparison allows investigation of the spatial correlation between b-value and strain rate maps and is thus able to locate fault segments that have a high potential of generating large earthquake(s). b-Values range from 0.5 to 1.5 along the central NAF. The maximum principal strain rates are positive (tensile), and the minimum principal strain rates are negative (compressive). The surface strain is positive, showing that tensile strain is predominant in areas with high strain rates, consistent with the trend of the corresponding stresses.

Study of seasonal and long-term vertical deformation in Nepal based on GPS and GRACE observations

Lithospheric deformation signal can be detected by combining data from continuous global positioning system (CGPS) and satellite observations from the Gravity Recovery and Climate Experiment (GRACE). In this paper, we use 2.5- to 19-year-long time series from 35 CGPS stations to estimate vertical deformation rates in Nepal, which is located in the southern side of the Himalaya. GPS results were compared with GRACE observations. Principal component analysis was conducted to decompose the time series into three-dimensional principal components (PCs) and spatial eigenvectors. The top three high-order PCs were calculated to correct common mode errors. Both GPS and GRACE observations showed significant seasonal variations. The observed seasonal GPS vertical variations are in good agreement with those from the GRACE-derived results, particularly for changes in surface pressure, non-tidal oceanic mass loading, and hydrologic loading. The GPS-observed rates of vertical deformation obtained for the region suggest both tectonic impact and mass decrease. The rates of vertical crustal deformation were estimated by removing the GRACE-derived hydrological vertical rates from the GPS measurements. Most of the sites located in the southern part of the Main Himalayan Thrust subsided, whereas the northern part mostly showed an uplift. These results may contribute to the understanding of secular vertical crustal deformation in Nepal.

Estimation of present-day glacial isostatic adjustment, ice mass change and elastic vertical crustal deformation over the Antarctic ice sheet

ABSTRACTThis study explores an iterative method for simultaneously estimating the present-day glacial isostatic adjustment (GIA), ice mass change and elastic vertical crustal deformation of the Antarctic ice sheet (AIS) for the period October 2003–October 2009. The estimations are derived by combining mass measurements of the GRACE mission and surface height observations of the ICESat mission under the constraint of GPS vertical crustal deformation rates in the spatial domain. The influence of active subglacial lakes on GIA estimates are mitigated for the first time through additional processing of ICESat data. The inferred GIA shows that the strongest uplift is found in the Amundsen Sea Embayment (ASE) sector and subsidence mostly occurs in Adelie Terre and the East Antarctica inland. The total GIA-related mass change estimates for the entire AIS, West Antarctica Ice Sheet (WAIS), East Antarctica Ice Sheet (EAIS), and Antarctic Peninsula Ice Sheet (APIS) are 43 ± 38, 53 ± 24, −23 ± 29 and 13 ± 6 Gt a−1, respectively. The overall ice mass change of the AIS is −46 ± 43 Gt a−1 (WAIS: −104 ± 25, EAIS: 77 ± 35, APIS: −20 ± 6). The most significant ice mass loss and most significant elastic vertical crustal deformations are concentrated in the ASE and northern Antarctic Peninsula.

Late Quaternary crustal shortening rates across thrust systems beneath the Ou Ranges in the NE Japan arc inferred from fluvial terrace deformation

We documented the existence of a blind thrust along the volcanic front in northeast Japan and calculated the crustal shortening rate across the Ou Ranges. We detected broad anticlinal deformation of the longitudinal profiles of fluvial terraces dated by using tephro- and cryptotephrostratigraphy. We inferred that the Daizaki flexure, located along the southern extension of the 2008 Iwate-Miyagi Nairiku Earthquake (IMEQ) fault, indicated the presence of an underlying thrust (Daizaki fault, newly named) there. Therefore, we inferred the existence of a west-dipping thrust system along the volcanic front at the eastern edge of the Ou Ranges consisting from north to south of the Kitakami Teichi Seien Fault Zone, the 2008 IMEQ fault and the Daizaki fault. To estimate rates of crustal deformation due to this thrust, we determined the uplift rate distribution from a pair of accumulation terrace surfaces, one formed during the marine isotope stage (MIS) 6–5 glacial-to-interglacial transition and the other during the MIS 2–1 transition. Because the overall uplift-rate distribution includes crustal deformation at both regional and local scales, we calculated the fault-related deformation area by subtracting the regional uplift rate (0.15–0.18mky−1, obtained from a pair of fluvial terraces on the stable footwall) from the total uplift-rate distribution across the fault. A mass balance calculation of the fault-related deformation area showed the crustal shortening rate across the 2008 IMEQ fault to be 0.50±0.19–0.59±0.22mky−1. An east-dipping thrust system along the western edge of the Ou Ranges (eastern part of the Shinjo Basin Fault Zone) has also contributed to crustal shortening during the late Quaternary at a previously estimated rate of 0.65–1.42mky−1. Therefore, the shortening rates of the eastern and western thrust systems individually account for about 0.6–0.7% and 0.7–1.6%, respectively (total, 1.3–2.3%), of the convergence between the Pacific and Eurasian plates. This westward increase in the shortening rate across the Ou Ranges is in accordance with the crustal structure, which reflects the tectonic history since the Miocene backarc spreading of the Japan Sea.

Extension rates across the northern Shanxi Grabens, China, from Quaternary geology, seismicity and geodesy

Discrepancies between geological, seismic and geodetic rates of strain can indicate that rates of crustal deformation, and hence seismic hazard, are varying through time. Previous studies in the northern Shanxi Grabens, at the northeastern corner of the Ordos Plateau in northern China, have found extension rates of anywhere between 0 and 6 mm/a at an azimuth of between 95 and 180 °. In this paper we determine extension rates across the northern Shanxi Grabens from: offset geomorphological features and a variety of Quaternary dating techniques (including new IRSL and Ar-Ar ages); a Kostrov summation using a 700 year catalogue of historical earthquakes; and recent campaign GPS measurements. We observe good agreement between Quaternary, seismic and geodetic rates of strain, and we find that the northern Shanxi Grabens are extending at around 1 to 2 mm/a at an azimuth of ≈ 151 °. The azimuth of extension is particularly well constrained and can be reliably inferred from catalogues of small earthquakes. We do not find evidence for any substantial variations in extension rate through time, though there is a notable seismic moment rate deficit since 1750. This deficit could indicate complex fault interactions across large regions, aseismic accommodation of deformation, or that we are quite late in the earthquake cycle with the potential for larger earthquakes in the relatively near future.

Crustal deformation rates in Assam Valley, Shillong Plateau, Eastern Himalaya, and Indo-Burmese region from 11 years (2002–2013) of GPS measurements

The present study reports the contemporary deformation of the tectonically complex northeast India using 11 years (2002–2013) of GPS observations. The central Shillong Plateau and few sites north of Plateau located in Assam Valley behave like a rigid block with ~7 mm/year India-fixed southward velocity. The Euler pole of rotation of this central Shillong Plateau–Assam Valley (SH–AS) block is estimated to be at −25.1° ± 0.2°N, −97.8° ± 1.8°E with an angular velocity of 0.533° ± 0.10° Myr−1 relative to India-fixed reference frame. Kopili fault located between Shillong Plateau and Mikir massif records a dextral slip of 4.7 ± 1.3 mm/year with a locking depth of 10.2 ± 1.4 km indicating the fragmentation of Assam Valley across the fault. Presently, western edge of Mikir massif appears to be locked to Assam block indicating strain accumulation in this region. First-order elastic dislocation modelling of the GPS velocities estimates a slip rate of 16 mm/year along the Main Himalayan Thrust in Eastern Himalaya which is locked over a width of 130 km from the surface to a depth of 17 km with underthrusting Indian plate. Around ~9 mm/year arc-normal convergence is accommodated in Lesser Himalaya just south of Main Central Thrust indicating high strain accumulation. Out of 36 mm/year (SSE) India-Sunda plate motion, about ~16 mm/year motion is accommodated in Indo-Burmese Fold and Thrust Belt, both as normal convergence (~6 mm/year) and active slip (~7–11 mm/year) in this region.

Comparison of the historic seismicity and strain-rate pattern from a dense GPS-GNSS network solution in the Italian Peninsula

We present a dense crustal velocity field and corresponding strain-rate pattern computed using Global Positioning System (GPS)- Global Navigation Satellite System (GNSS) data from several hundred permanent stations in the Italian Peninsula. GPS data analysis is based on the GAMIT/GLOBK 10.6 software, which was developed and maintained mainly by Massachusetts Institute of Technology (MIT), using tools based on the distributed-sessions approach implemented in this package. The GPS data span the period from January 2008 to December 2012 and come from several different permanent GPS networks in Italy. The GLOBK package implemented in the last version of the GAMIT package is used to compute the position time-series and velocities registered in the International Terrestrial Reference Frame (ITRF) 2008. The resulting high-density intra-plate velocity field provides indications of the tectonics of the Mediterranean region. A computation of the strain-rate pattern from GPS data is performed and compared with the map of the epicentral locations of historical earthquakes that occurred in the last 1000 years in the Italian territory, showing that, in general, higher crustal deformation rates are active in regions affected by seismicity of greater magnitude.

Geodetic analysis of post-seismic crustal deformations occurring in South Korea due to the Tohoku-Oki earthquake

Despite its low frequency of resident earthquakes, the Korean Peninsula is indirectly affected by the large earthquakes occurring in the Japanese Islands. In this study, GPS coordinate time series were analyzed to examine the changes in the crustal movement of the Korean Peninsula due to the 2011 Tohoku-Oki (TO) earthquake. A comparison of the pre- and post-seismic crustal deformation velocities indicated that the crustal movements of the Korean Peninsula had a velocity of 29 mm/year and an azimuth of 113° before the earthquake, and a velocity of 36 mm/year and an azimuth of 108° after the earthquake. Therefore, the crustal movement velocity significantly increased, and the direction of the movement headed more eastward compared to that before the earthquake. The calculation of the progress rate of the post-seismic crustal deformation after eliminating the Euler pole velocity and annual cycle signal from the coordinate time series showed that about 80% of the total post-seismic crustal deformation had progressed in the Korean Peninsula. In addition, analysis of principal strain change indicated that for the principal strain applied to the Korean Peninsula, the east-west dilatation increased and the north-south contraction decreased compared to those in the co-seismic stage.

Present-day crustal deformation along the El Salvador Fault Zone from ZFESNet GPS network

This paper presents the results and conclusions obtained from new GPS data compiled along the El Salvador Fault Zone (ESFZ). We calculated a GPS-derived horizontal velocity field representing the present-day crustal deformation rates in the ESFZ based on the analysis of 30 GPS campaign stations of the ZFESNet network, measured over a 4.5year period from 2007 to 2012. The velocity field and subsequent strain rate analysis clearly indicate dextral strike–slip tectonics with extensional component throughout the ESFZ. Our results suggest that the boundary between the Salvadoran forearc and Caribbean blocks is a deformation zone which varies along the fault zone. We estimate that the movement between the two blocks is at least ~12mmyr−1. From west to east, this movement is variably distributed between faults or segments of the ESFZ. We propose a kinematic model with three main blocks; the Western, Central and Eastern blocks delimited by major faults. For the first time, we were able to provide a quantitative measure of the present-day horizontal geodetic slip rate of the main segments of ESFZ, ranging from ~2mmyr−1 in the east segment to ~8mmyr−1, in the west and central segments. This study contributes new kinematic and slip rate data that should be used to update and improve the seismic hazard assessments in northern Central America.