Right-lateral Motion Research Articles

Spatial variation of the source mechanisms in the Egyptian continental margin

The spatial variability of the focal mechanism solutions in the NW Egypt Cyrenaica and Levant-north Egypt domains of the Egyptian Continental margin is investigated based on the polarity of the P-wave first motions of eleven earthquakes with local magnitudes ML ranging from 4.2 to 6.2. The identified focal mechanism solutions in the Levant-north Egypt domain are evaluated in two sub-provinces with different geological settings. The first sub-province shows strike-slip faulting mechanisms with right-lateral motion along the NE-trending Rosetta-Qattara fault zone, while the NW-trending Temsah fault zone produces left-lateral strike-slip motion. The inland extension of the Rosetta-Qattara fault zone towards the Western Desert reflects the same sense of motion. Strike-slip faulting with thrust components dominates the focal mechanisms in the second sub-province but with a different stress orientation. A single thrust faulting mechanism event which occurred on the periphery of the continental shelf shows the same common orientation of the stress field at the Hellenic Arc. This type of mechanism in this locality can be explained by the mean of compressional stress transfer towards the coast generated by the accelerated southwest retreat of the Hellenic Trench. The complex regional stress along the Cyprian and Hellenic arcs, the current local structure features, and the dominant orientation of the pre-existing fault are the factors that contribute to the changeable stress pattern field in the Levant-north Egypt domain. A single event in the second domain, the NW Egypt Cyrenaica, is a strike-slip with a right-lateral sense of motion on a WNW-oriented plane, consistent with motion along the WNW tectonic fault which separates the continental shelf from the oceanic crust.

Strain partitioning, transfer and implications for the ongoing process of intracontinental graben formation in the northwestern margin of the Ordos block, China: insights from densified GNSS measurements

SUMMARY The northwestern margin of the Ordos block is structurally separated by the Yinchuan–Hetao graben system. As one of the most active intracontinental graben systems within the Eurasian continent, its kinematic pattern of crustal extension is crucial for unraveling the ongoing processes of intracontinental graben formation, while it remains unclear principally due to a lack of geological constraints on crustal deformation. We obtained and analysed a densified GNSS (Global Navigation Satellite System) velocity field in this region. Our results suggest that the western margin of the Hetao graben exhibits the NW-directed crustal extension (∼ 1.1 mm yr−1), which can be attributed to the conjugate transtension resulting from the left-lateral motion along the E–W-trending northern boundaries of the Alashan and Ordos blocks, as well as the right-lateral motion along the N–S-trending western margin of the Ordos block. Additionally, in response to the NE-directed extrusion of the Tibetan Plateau, the Alashan block undergoes approximately NE-directed contraction (4.9 ± 1.1 nanostrain yr−1) and NW-directed extrusion (2.8 ± 0.8 nanostrain yr−1), which vacates space for the crustal extension of the Yinchuan graben with a rate of 0.9 ± 0.1 mm yr−1. Although it is challenging to determine whether the left-lateral motion (approximately 1 mm yr−1) along the E–W-trending Hetao graben is the far-field effect of western Pacific subduction, the gradual decrease in right-lateral motion from the N–S-trending western margin of the Ordos block toward the north side of the Yinshan Orogen manifests the far-field effect of the Indo-Eurasian plate convergence extending into the Mongolian Plateau.

Geomorphic impacts within Red River Fault and island shifting as witnessed by the phylogeography of the largest water strider

Palaeogeological events and climate oscillations profoundly impact the demographics and distributions of small-range species, increasing the extinction risk. The largest water strider worldwide, Gigantometra gigas (Hemiptera: Gerridae), exhibits restricted distributions in Vietnam and southern China. Herein, we generated three genomic datasets (mitogenomes, 146 nuclear protein-coding genes and single nucleotide polymorphisms) with ecological niche modelling (ENM) to explicitly test whether the present-day distribution of G. gigas actually resulted from geographical and climatic effects. We found that the origin of this largest water strider reached the divergence time of the genus within Gerridae, providing a greater opportunity to explore its response to geographic movements. The right-lateral motion of the Red River Fault facilitated the divergence of two phylogeographic lineages, resulting in the “north–south component” genetic pattern in G. gigas. The Hainan and southeast Vietnam populations of the southern linage were completely separated by the Beibu Gulf but exhibited similar genetic compositions, confirming that Hainan had a continental origin and that Hainan Island joined with the Indo-China Peninsula to promote gene exchange among populations. Additionally, we noticed the low genetic diversity but long demographic history of the northern lineage, which displayed population dynamics opposite to those of other organisms. Integrating the demographic changes and ENM findings revealed that suitable habitat contraction and rapid demographic decline during the Last Glacial Maximum (LGM) triggered the low genetic diversity of the northern lineage. Overall, the demographic history of the largest water strider was mainly shaped by geographical features, and first provided evidence from the phylogeographic perspective of aquatic insects to support the hypothesis of Hainan Island shifting.

Why does western Makran have a low seismicity rate?

The Makran Subduction Zone is segmented into western and eastern Makran where all instrumentally recorded megathrust earthquakes happened in eastern Makran. To find out how the lack of megathrust earthquakes and the observed low seismicity rate in western Makran is related to a combination of long interseismic quiescence, aseismic creep, or low rate of interseismic strain accumulation within the megathrust zone, we have complemented the five existing GPS vectors along the coasts of Makran by nine new GPS vectors and an extra eight new GPS vectors across the width of the Makran megathrust zone. Our block modeling shows that the coupling of the subducting Arabian oceanic plate with the overriding plate in western Makran is more than four times smaller than that of eastern Makran. Additionally, the maximum interseismic strain rate accumulation within the onshore part of the megathrust zone of western Makran is >7 times smaller than that in eastern Makran. We found a right-lateral motion of about ∼16 mm across the transfer zone between Zagros and Makran. We consider a much lower earthquake hazard for western Makran relative to that of eastern Makran because the overriding Lut block is moving northward causing much less strain accumulation within the megathrust zone, and because of the lower seismic coupling between the subducting and overriding plates. Our findings show a large strain rate across the transfer zone between Zagros and Makran and thus imply a much higher earthquake hazard for the transfer zone.

Mechanics of the Kalabagh Fault, northwest Himalayan fold and thrust belt (convergence zone of India and Eurasia), using SAR interferometry and CFS

The Kalabagh strike–slip fault, which is characterized by right-lateral movement, is part of the northwestern Himalayan foreland fold and thrust belt in Pakistan. This structure marks the western and eastern terminations of the Salt Range and Surghar Ranges, respectively. No significant (>M6) earthquakes have been reported along the Kalabagh Fault in recent decades. Here, we take advantage of space-borne Sentinel-1A SAR interferometry to gain insight into the mechanics of faulting, aseismic creeping, and stress loading of the seismic cycle on the Kalabagh Fault spanning over approximately 7 years. In this study, we also removed the tropospheric effects using the Generic Atmospheric Correction Online Service data from the rate map. We further resolved the LOS deformation into both horizontal and vertical deformations. Our Bayesian inversion indicates that the fault experiences significant horizontal and vertical displacements. The fault’s southern and northern segments exhibit a creeping rate of approximately ∼4.2 ± 1.3 to 4.8 ± 1.6 mm/year, respectively, while the central section does not display any horizontal creeping. We found that the creeping is confined between 0 and ∼2.7 ± 1.1 km depth at the northern section and 0 and ∼3.9 ± 1.1 km on the southern section of the faults. Nevertheless, we found that the vertical creeping of ∼10 mm/year is confined between 0.5 and 6 km depth in the central segment of the fault. Moreover, our model does not resolve the interseismic slip at depth on the Kalabagh Fault. Our results affirm that Kalabagh Fault is creeping, and the internal deformation due to the presence of a thick salt layer over the decollement facilitates the creeping on this fault. In addition, Coulomb stress modeling depicts that the creeping on the Kalabagh Fault increases the Coulomb stress changes in the northern section of the KBF.

“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.

Interseismic deformation and strain-partitioning along the Main Köpetdag Fault, Turkmenistan, with Sentinel-1 InSAR time-series

SUMMARY The Main Köpetdag Fault (MKDF) is a predominantly right-lateral strike-slip fault that dissects the northern edge of the Köpetdag mountains of Turkmenistan and Iran. The fault represents the northernmost expression of deformation from the Arabia–Eurasia collision to the east of the Caspian Sea, and plays an important role facilitating the motion of the South Caspian Basin (SCB). Despite the kinematic significance of the MKDF, previous geodetic measurements of the slip-rate across the fault have been highly variable, with a recent geological slip-rate supporting evidence for rapid motion across the fault. To resolve this ambiguity, we derive Sentinel-1 InSAR time-series in both the ascending and descending LOS (line-of-sight) to measure interseismic motion across the MKDF. This implements a processing strategy for the correction and performance analysis of tropospheric models from GACOS (Generic Atmospheric Correction Online Service), which suggests a 25–40 per cent underestimation in the amplitude of the tropospheric path delay in this region. Modelling the rate of fault-parallel motion across the MKDF and combining this with a geological slip-rate constrains 9 ± 2 mm yr–1 right-lateral motion, along with a shallow locking depth of ≈6 km. The LOS time-series resolves path delays of greater than 1 mm yr–1 in both LOS geometries to the north of the MKDF, aligned with mapped frontal thrust scarps to the north of the MKDF. Modelling this as uplift from deformation across these frontal thrusts estimates 4 ± 2 mm yr–1 of shortening across the fault system. This implies that convergence measured with GNSS within the East Caspian Lowlands is partitioned across frontal thrusts to the north of the MKDF. Revising an Iran–Eurasia–SCB velocity triangle suggests that motion along the conjugate MKDF and Shahroud fault zones is representative of the motion of the SCB, which is moving at 10 ± 2 mm yr–1 in a direction of 330° ± 10° relative to Eurasia.

Separation of Gagua Rise from Great Benham Rise in the West Philippine Basin during the Middle Eocene

The West Philippine Basin (WPB) has started opening at ~ 58 Ma and ceased spreading at ~ 33 Ma, developing a fast spreading (~ 44 mm/yr half-spreading rate) magmatic episode between 58 and 41 Ma and the second amagmatic episode between 41 and 33 Ma. The occurrence of the first stage of spreading is closely related to the Oki-Daito mantle plume and related Benham Rise (BR) and Urdaneta Plateau (UP) activity. To the east of the Luzon–Okinawa Fracture Zone (LOFZ), BR was the most active volcanism from 48 to 41 Ma. The geomagnetic ages on both sides of the LOFZ have been determined; however, their causal relationship and evolution in the WPB remain unclear. In this study, we performed integrated analyses of multichannel seismic data and swath bathymetry data for the area to the west of the LOFZ. To the west of the LOFZ, the Gagua Rise (GR), is identified by a high residual free-air gravity anomaly, volcanic seamount chains and an overlapping spreading center. The GR is located at magnetic isochrons C20/C22 (50 to 44 Ma) and shows a thick oceanic crust of at least 12.7 km. We first propose an oceanic plateau named Great Benham Rise (GBR) which includes GR, UP and BR. We infer that the GR was a portion of the GBR since ~ 49 Ma and was separated from the GBR at ~ 41 Ma by the right-lateral LOFZ motion. Later, the relict GBR magmatism only continued in the area to the east of the LOFZ. Overall, the GBR dominates the spreading history of the WPB.

Neotectonics of the Western Suleiman Fold Belt, Pakistan: Evidence for Bookshelf Faulting

The Suleiman Fold-Thrust Belt represents an active deformational front at the western margin of the Indian plate and has been a locus of major earthquakes. This study focuses on the western part of the Suleiman Fold-Thrust Belt that comprises two parallel NW–SE oriented faults: Harnai Fault and Karahi Fault. These faults have known thrust components; however, there remains uncertainty about the lateral component of motion. This work presents the new observation of surface deformation using the Small Baseline Subset (SBAS), Interferometric Synthetic Aperture Radar (InSAR) technique on Sentinel-1A datasets to decompose displacement into the vertical and horizontal components employing ascending and descending track geometries. The subsurface structural geometry of this area was assessed using 2D seismic and well data. In addition, geomorphic indices were calculated to assess the relative tectonic activity of the area. InSAR results show that the Karahi Fault has a ~15 mm right-lateral movement for descending and ~10 mm/for ascending path geometries. The Harnai Fault does not show any lateral movement. Seismic data are in agreement with the InSAR results suggesting that the Harnai Fault is a blind thrust. This work indicates that the block between these two faults displays a clockwise rotation that creates the “bookshelf model”.

لرزه زمین ساخت پهنه های البرز خاوری و کپه داغ با استفاده از داده های شبکه لرزه نگاری محلی

The Kopeh Dagh and Binalud-Alla Dagh mountains are important structural elements located in the northeastern boundary of Arabia-Eurasia collision zone. Due to existence of large cities with a long history of civilization, there is a relatively rich body of data on historical seismicity in this area. Nonetheless, little adequate instrumental seismic data were available prior to this study. In this paper, we utilized the temporary China-Iran local seismic network data deployed in the area for 13 months. Based on this data, we determined 37 focal solutions through first motion polarity approach suggesting a combination of strike-slip, reverse and normal mechanisms. There is a significant concentration of epicenters and focal mechanisms around the eastern Alborz - Kopeh Dagh boundary along the Atrak River. The southern and western boundaries of the Binalud Mountains also show relatively high seismic activities. The Local magnitude (ML) of the events ranges from 3.5 to 4.9 with depths of up to 20 km, mostly concentrated at ~10 km. The principal stress axes and slip vectors obtained from the focal mechanisms agree well with kinematic state of main faults and tectonic regime of the area, confirming the seismogenic nature of these faults. In addition, they are consistent with right-lateral component of slip along thrust faults in eastern Kopeh Dagh and Binalud and both laft- and right-lateral motions in the central Kopeh Dagh.

Stress field and tectonic regime of Central Iran from inversion of the earthquake focal mechanisms

This paper provides a latest compilation of data on the present-day stress pattern in Central Iran and its tectonic regime. We compiled 103 focal mechanism data collected from the Global Centroid Moment Tensor Project (GCMT) including data from Harvard University (HRVD) and the International Seismological Center (ISC). Stress inversion of all shallow focal depths provides a first order stress field with a N029°E maximum horizontal compressive stress (SHmax) direction corresponding to a general compressive tectonic regime. In order to reconstruct the second and third order stress fields, we subdivided the study area into eight zones on the basis of their structures, relatively similar focal mechanisms and relatively homogeneous deformation. For each zone and for the same data set, reduced stress tensors have been obtained by formal stress inversion using the Win-Tensor program and modified SLICK method. Both inversion methods show similar results for horizontal stress axes orientations and for the tectonic regimes.The obtained NE-SW direction of the first order stress field is related to Arabia-Eurasia convergence as confirmed by the geodetic measurements. This stress field is responsible for accommodation of shortening within Central Iran and right-lateral movement along the N-S faults as well as left-lateral movement along the E-W faults. Solid block rotation between strike-slip and thrust faults, vertical rotation of the fault bounded blocks, escape tectonics, block extrusion and strain partitioning occurred due to second and third order stress fields with variable SHmax directions from N006° to N081° and in different tectonic regimes.

Tectonic stress regime and stress patterns from the inversion of earthquake focal mechanisms in NW Himalaya and surrounding regions

Because the impact of earthquake effects can extend over great distances from their origin, stress field inversion was performed for 440 earthquake focal mechanisms from the northwest Himalayas and surrounding regions compiled from the data bulletins of international seismological institutions. Earthquakes between November 1976 and April 2019 in the depth range of 10–258 km with moment magnitudes between 4.6 and 7.9 were selected. High-quality solutions were inverted to locate the best fitting stress tensor. Most of the earthquake fault plane solutions indicated thrust faulting, confirming northward underthrusting of the Indian plate along the Main Boundary Thrust and the Main Central Thrust systems and eastward underthrusting along the Burmese Arc. The focal mechanisms indicated right-lateral motion along the Karakoram Fault and left-lateral motion along the Kirthar–Sulaiman Range, which agrees with the expected sense of the lateral mass movement of the continental collision model. The present-day stress regimes obtained from the earthquake focal mechanism inversions indicated a predominantly compressional stress regime represented by NNE–SSW trending normal fault mechanisms in northwest India and Nepal and NNW–SSE trending normal fault mechanisms in Pakistan and Hindukush. These are consistent with the direction of the ongoing India–Eurasia plate collision and the extensional stress of WNW–ESE trending thrust faulting in the Xizang and Kashmir regions. These tectonic regimes connected with the major tectonic affecting the Arabian Peninsula. Accordingly, it is highly recommended to assess the earthquake hazards of the major cities in the eastern countries of Arabian Peninsula as Kuwait, Saudi Arabia, United Arab Emirates and Oman.

Updated Segmentation Model and Cummulative Offset Measurement of the Aceh Segment of the Sumatran Fault System in West Sumatra, Indonesia

Sumatran fault in western Indonesia is one of the largest strike-slip fault in the world. The fault was formed as a result of the slip partitioning of the oblique convergence between the Indo-Australian and Eurasian plate along the Sunda trench. The right-lateral movement of the fault is accomodated by 19 fault segments that dissects the entire Sumatra island. We study the Aceh fault segment, which is located at the northernmost parts of the fault. The Aceh fault segment spans 250 km long passing through three districts: West Aceh, Pidie Jaya, and Aceh Besar and is affecting a total of ~546.143 population in the area. The current segmentation model assumes that Aceh fault segment acts as a single fault segment, which would generate closer to a M8 earthquake. This estimation is inconsistent with the ~M6-7 historical earthquake data. We conduct a detailed active fault mapping using the ~8 m resolution digital elevation model of DEMNAS and the sub-m DEM data from UAV-based photogrammetry to resolve the segmentation model of this fault. Our study indicate that the Aceh fault segment can be divided into 8 subsegments: Beutong, Kuala Tripa, Geumpang, Mane, Tangse, Jantho, Indrapuri, and Pulo Aceh. The fault kinematics identified in the field is consistent with right-lateral faulting. We measured cumulative displacement of geomorphic features (channels and ridges) ranging from 12.7 to 1931 m at some area. Findings of our study provide better estimation of the fault geometry and the maximum magnitude of potential earthquake along the Aceh fault segment as well as recommendation of prospective sliprate study sites. These informations are important for the development of seismic hazard analysis of the area.

Quantitative assessment of the relative tectonic activity using the analytical hierarchy process in the northwestern margin of the Lut Block, Central Iran

In this study, the analytical hierarchy process (AHP) was used to enhance the accuracy of the results obtained from the geomorphic analysis of tectonic activity. For this purpose, the relative tectonic activity index was computed by applying different and specific weights to each index based on the general geological and structural conditions of the study area. The Kuh-e-Sarhangi Mountain with a NE-SW strike is located in the northern part of the Tabas Block in the Central Iran Plate. The Kuh-e-Sarhangi Fault is considered one of the major faults in Central Iran and shows evidence of Quaternary activity. In this study, in order to evaluate the activity of the faults, six morphotectonic indices were computed and the different conditions which influenced the morphometric factors were considered and analyzed. The relative tectonic activity of Kuh-e-Sarhangi was classified based on the analytical hierarchy process method. These results were confirmed by field studies. The results of this method fitted well with some independently detected Quaternary faults and other reactivated faults in the Kuh-e-Sarhangi Mountain. With a right-lateral movement, some of these faults have caused the displacement of rivers up to 900 m. The dispersal of the high tectonic activity classes based on the AHP method conforms to the post-Neogene activity of the region. The distribution of the classes illustrates that morphotectonic anomalies correspond with the incised alluvial fans and terraces and the bisected and displaced rivers in the study area. Accordingly, the integration of the results of field investigations, satellite images, morphometry, and the AHP method shows a high accordance with the active structures and demonstrates that the study area is tectonically active. This analysis illustrates the recent movements of the Kuh-e-Sarhangi Fault and the activity of the Lut Block due to the convergent movement of the Arabian plate toward Eurasia.

Lower Cretaceous stratigraphic characteristics and tectonic control of the eastern depression, North Yellow Sea Basin, North China

The Lower Cretaceous of the eastern depression in the North Yellow Sea Basin is a set of residual strata that can be divided into K1sq1 and K1sq2 sequences. There are four lithology–lithofacies architectures summarized in the third-order sequences of wells W5, W3, W1, W9, W16, W7, W8, and W10, and they are the coarse–fine–coarse, asymmetric coarse–fine, asymmetric fine–coarse, and interbedded coarse and fine. F1, F4, F6, and F7, which are strike-slip faults, were dominant during the Early Cretaceous, and controlled the eastern depression to undergo right-lateral movement from transtension to transpression. The tectonic movement controlled different stratigraphic structure in different areas, and the fan bodies deposited along the basin margin and progradated into the basin center. The sequence models under extensional and strike-slip setting were established respectively. The transtension–transpression movement controlled the development of the sandstones in the Lower Cretaceous and improved the quality of the reservoir rocks.

Active tectonics and GPS data analysis of the Maghrebian thrust belt and Africa-Eurasia plate convergence in Tunisia

The Atlas Mountains of Tunisia belong to the seismically active zone of the Africa (Nubia) - Eurasia plate boundary in the central-western Mediterranean. We study the eastern section of the Maghrebian thrust belt using a subset (6 days) from each of 5 years (2014 to 2018) of permanent (survey-mode) GPS data and active tectonics. WNW to NNW-trending velocities express crustal motion and geodetic strain fields from the Sahara Platform to the Tell Atlas, consistent with African plate convergence. To the south, the velocities and trajectories indicate nearly WNW-ESE-trending right-lateral motion of the Sahara fault-related Atlas fold belt with respect to the Sahara Platform. Farther north and northeast, the significant decrease in velocities between the Eastern Platform (Sahel), Central Atlas and Tell Atlas and the clockwise rotation mark the NNW-trending shortening deformation associated with local ENE-WSW extension visible in the Quaternary grabens. The velocity field and strain distribution associated with the active E-W- to WNW-ESE-trending right-lateral faulting and NE-SW fault-related folds illustrate the transpression tectonics and support the identification of four tectonic domains north of the Africa-Nubia Platform in Tunisia. The transpression reduces northward when reaching the Central and Tell Atlas. These results change our perception of the Africa-Eurasia plate boundary previously located along the western Mediterranean coastline.

The 2019 Mw 6.4 and Mw 7.1 Ridgecrest earthquake sequence in Eastern California: rupture on a conjugate fault structure revealed by GPS and InSAR measurements

SUMMARYOn 4 and 6 July 2019, an Mw 6.4 foreshock and an Mw 7.1 main shock successively struck the city of Ridgecrest in eastern California. These two events are the most significant earthquake sequences to strike in this part of California for the past 20 yr. We used both continuous global positioning system (GPS) measurements and interferometric synthetic aperture radar (InSAR) images taken by the Sentinel-1 and ALOS-2 satellites in four different viewing geometries to fully map the coseismic surface displacements associated with these two earthquakes. Using these GPS and InSAR measurements both separately and jointly, we inverted data to find the coseismic slip distributions and fault dips caused by the two earthquakes. The GPS-constrained slip models indicate that the Mw 7.1 main shock was predominately controlled by right-lateral motions on a series of northwest-trending faults, while the Mw 6.4 foreshock involved both right-lateral slipping on a northwest-trending fault and left-lateral slipping on a northeast-trending fault. The two earthquakes both generate significant surface slip, with the maximum inferred slip of 5.54 m at the surface. We estimate the cumulative geodetic moment of the two earthquakes to have been 4.93 × 1019 Nm, equivalent to Mw 7.1. Furthermore, our calculations of the changes in static Coulomb stress suggest that the Mw 7.1 main shock was promoted significantly by the Mw 6.4 foreshock. This latest Ridgecrest earthquake sequence ruptured only the northern part of the seismic gap between the 1992 Mw 7.3 Landers earthquake and the 1872 M 7.4–7.9 Owens Valley earthquake. The earthquake risk in this area, therefore, remains very high, considering the significant accumulation of strain in the Eastern California Shear Zone, especially in the southern part of the seismic gap.

Restoring the source-to-sink relationships in the Paleogene foreland basins in the Central and Southern Alps (Switzerland, Italy, France): a detrital zircon study approach

Late Paleogene syn-tectonic magmatic products are known from sandstones contained in the North Alpine (NAFB) and South Alpine (SAFB) foreland basins and in the South Alpine pelagic Trento Basin. The generally turbiditic and mass-flow deposits grade up from marly hemipelagic deeper water series. The source and amount of the reworked volcanic materials have been in debate for a long time. As a proxy for the magma-derived input we use the U–Pb geochronology and geochemistry [176Hf/177Hf(t) and Eu/Eu* ratios] of detrital zircons, and evaluate their temporal and genetic relationships with potential volcanic sources in the Periadriatic magmatic systems (Adamello, Bergell, Biella). The oldest volcanic sources (Lutetian–Priabonian) we identify are in the Trento Basin and Glarus NAFB. During most Rupelian, Bergell and Biella volcaniclastics were delivered to the NAFB in the Glarus, Alpe de Taveyanne and Haute-Savoie. Bergell and minor Adamello magmatic material were supplied to the Villa Olmo Conglomerate in the SAFB. During late Rupelian–Chattian in the entire NAFB, the influx of Paleogene volcanic material faded out. At the same time in the SAFB, the Como Conglomerate shows mixed input from Biella and Bergell. High numbers of old zircons (> 90%) in the NAFB document the asymmetry of the early Alpine orogenic wedge exposing large basement areas to the north of the Periadriatic intrusions. The syn-sedimentary right-lateral movement along the Periadriatic fault system is identified as the main driver of magmatic activity, uplift, and exposure to erosion and transport to the basins. On this base, the dynamics of the early Alpine drainage systems are reconstructed with new accuracy.

The Red River sediment budget in the Yinggehai and Qiongdongnan basins, northwestern South China Sea, and its tectonic implications

ABSTRACT The rapid uplift of the Tibetan plateau, the intense movement of the Ailao Shan-Red River Shear Zone (ARSZ), and the related climate change during the Cenozoic Indo-Asian collision have been widely studied; however, their timings varied considerably due to different data and methods used. As these events have been documented in the Red River sediment that came from the eastern Tibetan plateau and the Red River region and eventually deposited in the offshore Yinggehai and Qiongdongnan basins, here these events can be explored by calculating and analysing the Red River sediment budget, especially in the Qiongdongnan basin based on dense seismic profiles and wells. Results show that the Red River sediment mainly accumulated in the Yinggehai basin and the west part of the Qiongdongnan basin, and there are three sedimentary accumulation peaks in the Red River sediment budget during ~29.5–21, ~15.5–10.5, and ~5.5–0 Ma. By further comparing with previous studies on the timings of these events, it is inferred that the first sedimentary peak, prior to the onset of the monsoon intensification (~22 Ma), was probably driven by an intense left-lateral movement of the ARSZ in ~29.5–21 Ma. The second peak (~15.5–10.5 Ma), however, reflects a rapid uplift of the Tibetan plateau after the cessation of the left-lateral strike slip of the ARSZ. The third peak (~5.5–0 Ma) is most likely linked with a right-lateral movement of the ARSZ and the related climate change. Overall, the Red River sediment budget from the offshore Yinggehai and Qiongdongnan basins provides an important constraint on the timings of these tectonic events as well as the related climate change during the Cenozoic Indo-Asian collision.

Crustal motion and deformation in Ecuador from cGNSS time series

In this paper, we present the first velocity field from cGNSS (continuous GNSS) stations in the Continuous Monitoring GNSS Network (REGME) in Ecuador. We have analyzed data from 33 cGNSS REGME stations for the 2008–2014 period in order to characterize horizontal crustal motion and deformation in Ecuador. Prior to this, we analyzed the time series for the 33 REGME stations in order to determine their seasonality and the type of spectral noise. For most stations, we found a predominance of uncorrelated white noise with annual and semi-annual variations as the predominant first and second periods. Velocity was estimated by introducing the trend, seasonality and noise in each series in the general model, thus allowing us to improve accuracy as well as magnitude. The velocity and strain distribution correspond to the transpressive right-lateral slip of the westward-dipping faults of the Major Dextral System and the NNE movement of the North Andean Block (NAB) relative to the South American plate. The distributions of our deformation rate and velocity field indicate a differentiated tectonic behavior between northern, central and southern Ecuador. In northern Ecuador, there is an estimated right-lateral motion of 7.6 ± 0.5 mm/yr, consistent with the NNE movement of the NAB relative to the South American plate. In central Ecuador, the right-lateral motion decreases to 5.3 ± 0.4 mm/yr. In the southern region of Ecuador (from the Guayaquil Gulf to Peru) there is no strain accumulation, GNSS velocities decrease and turn to south. This zone belongs to the so-called Inca or Peru sliver.These results are consistent with the distinct behavior of subduction in Ecuador, with no coupling in southern Ecuador, and increased coupling towards the north, in the zone where megathrust earthquakes have occurred over the last century. The southern part of the Carnegie Ridge marks the limit between the two zones.We suggest that the main driving force responsible for the ongoing crustal deformation in Ecuador is the convergence between the Nazca and South American plates with the variable coupling pattern and the collision of the Carnegie Ridge. This results in different velocity patterns for the northern and the southern parts of Ecuador.