Fault Kinematics Research Articles

Coseismic deformation and multi-fault slip model of the 2019 Mindanao earthquake sequence derived from Sentinel-1 and ALOS-2 data

From October to December 2019, a sequence of four earthquakes of Mw > 6.0 occurred in southern Mindanao, the Philippines, and revealed complex tectonics in this region. We used Advanced Land Observing Satellite (ALOS)-2 and Sentinel-1A/B Synthetic Aperture Radar (SAR) data to map the coseismic deformation and to constrain both the fault geometry and kinematics of coseismic slip distributions during the four earthquakes. Our observed coseismic deformation field shows that these four earthquakes ruptured two intersected conjugate faults with NE and NW strikes. Based on ascending and descending Interferometric SAR (InSAR) data, we constructed elastic half-space models to search for the optimal fault dip angle and inverted the slip distributions of the four earthquakes. The results show that these four earthquakes were all dominated by left- and right-lateral strike-slip motion. The two conjugate faults clearly had significant differences in terms of slip behaviour and fault kinematics. The static Coulomb stress change indicates that earlier earthquakes had a significant triggering effect on subsequent earthquakes. The static Coulomb stress change induced by the four earthquakes suggests a significant stress loading effect on NW-trending faults. The results of this study show that the potential for future earthquakes on NW-trending faults cannot be ignored; however the magnitudes of future earthquakes should be limited by complex fault geometry and segmentation.

GEOLOGICAL-AND-TECTONIC CONDITIONS OF FORMATION AND FOCAL MECHANISM OF TORAIGYR-SOGUETY EARTHQUAKE

The seismic characteristic of Toraigyr-Soguety earthquake is presented. The significant seismic events of the area are demonstrated including Chilik catastrophic earthquake. Geological-and-tectonic conditions of the epicentric areas of Chilik and Toraigyr-Soguety earthquakes are described. Kinematics of neotectonic faults is considered with respect to directions of main stress axes. Two models of focal mechanism of Toraigyr-Soguety earthquake compare with tectonic deformations of the area.

DZHIRGA EARTHQUAKE on April 27, 2014, Mw=4.9, КР=13.3, I0=7 (Northern Baikal Region)

We consider the April 27, 2014, Mw=4.9 Dzhirga earthquake, occurred within the north-eastern end of the Barguzin Depression. The event is the second one by energy level in the study area for the period of instrumental observations. The earthquake was followed by an aftershock sequence of 75 weak shocks recorded till the end of the year. The focal mechanism was determined from surface wave records from 13 digital broadband seismic stations of the IRIS networks. The obtained solution demonstrates the normal fault kinematics with both nodal planes striking north-east that corresponds to the regional fault pattern. The focal depth is estimated equal to 19 km. The maximum observed intensity was 5 points on the MSK-64 scale at the epicentral distance of 13 km. The Dzhirga earthquake analysis made it possible to fill in the lack of seismological information about the study area. The data obtained can be used for refinement of seismic hazard assessment of the north of the Barguzin Basin.

Structural Analysis of a Fault-related Anticline in the Southwestern Gyeonggi Massif, Korea Using an Unmanned Aerial Vehicle and Field Surveys: The Role of Rejoining Splays in a Duplex-like Structure

Kim, I.; Park, S.-I., and Lee, H.-J., 2020. Structural analysis of a fault-related anticline in the southwestern Gyeonggi Massif, Korea using an unmanned aerial vehicle and field surveys: The role of rejoining splays in a duplex-like structure. In: Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T. (eds.), Advances in Geospatial Research of Coastal Environments. Journal of Coastal Research, Special Issue No. 102, pp. 261-270. Coconut Creek (Florida), ISSN 0749-0208.In fold and thrust belts, various contractional structures accommodate horizontal shortening and vertical thickening in response to orogenic events. In this study, it was conducted a structural analysis of the Gomseom anticline, exposed along the coast in a part of a Phanerozoic orogenic belt in the southwestern Gyeonggi Massif, on the southern Korean Peninsula. To combat difficulties related to accessing the outcrop under tidal effects, high-resolution unmanned aerial vehicle (UAV) images alongside field data was used. The UAV photography technique allowed easy macro and mesoscale structural mapping and down-plunge projection, thereby enabling the efficient interpretation of the geometric and kinematic features of the Gomseom anticline. In the core of the Gomseom anticline, fault-bounded sheets are vertically stacked and folded, giving rise to a unique structural geometry analogous to duplexes. This duplex-like structure is bounded by a submerged thrust at the base and tightly folded thrust imbrication at the top and defined by intervening shortcut rejoining splays branching from the latter. Taking the kinematics of the sheet-bounding faults and intra-sheet minor faults into account, it was suggested an evolutionary model of the Gomseom anticline in which repeated fault-related folding and sequential propagation of rejoining splays give rise to the duplex-like structure. In the rejoining splay model, displacement on the basal thrust is transferred to a passive-roof thrust without hard links between them. Our result can be evaluated as a possible alternative duplex model that contrasts pre-existing models such as “Boyer-type”, “connecting splay”, and “fold” duplexes. However, further testing of the model is required.

Differential faulting in a narrow rift basin influenced by synchronous strike-slip motion: The Liaodong Bay sub-basin, offshore Bohai Bay Basin, China

Throughout the synrift stage of the Liaodong Bay sub-basin, offshore the Bohai Bay Basin in China, strike-slip motion within the Tan-Lu Fault Zone (TLFZ) greatly affected the local structural evolution. This led to abundant strike-slip, extension, and transtensional structural deformations within the Liaodong Bay sub-basin. The role played by the TLFZ in the evolution of the Bohai Bay Basin, however, remains unclear. This study evaluates the geometry and kinematics of faults and related structural styles within the Liaodong Bay sub-basin. Results reveal that very different structural deformations occurred across this long and narrow rift sub-basin, and show a shift of fault activity over time from west to east, and from extension to strike-slip. These differences in structural deformation across the basin indicate that strike-slip movement along the TLFZ mainly played a secondary role within the eastern part of the sub-basin, and was not responsible for the opening of the whole basin. Furthermore, it also indicates that the extensional and strike-slip dominated deformations within this sub-basin were driven by different geodynamics. The driving mechanism for strike-slip reactivation of the Cenozoic TLFZ is the subduction of the Pacific Plate beneath the eastern margin of the Asia continent. Differential faulting has also exerted an obvious influence on basin filling and hydrocarbon accumulation of the Liaodong Bay sub-basin.

InSAR 3-D Coseismic Displacement Field of the 2015 Mw 7.8 Nepal Earthquake: Insights into Complex Fault Kinematics during the Event

The 2015 Mw 7.8 Gorkha, Nepal, earthquake occurred in the central Himalayan collisional orogenic belt, which demonstrated complex fault kinematics and significant surface deformation. The coseismic deformation has been well documented by previous studies using Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR) data. However, due to some limitations of spatially sparse GPS stations and InSAR only-one-dimensional observation in the line-of-sight (LOS) direction, the complete distribution and detailed spatial variation of the three-dimensional surface deformation field are still not fully understood. In this study, we reconstructed the three-dimensional coseismic deformation fields using multi-view InSAR observations and investigated the refined surface deformation characteristics during this event. We firstly obtained four ascending and descending InSAR coseismic deformation maps from both Sentinel-1A/B and ALOS-2 data. Secondly, we obtained the synthetic north-south deformation field from our best-fitting slip distribution inversions. Finally, we calculated three-dimensional deformation fields, which were consistent with coseismic GPS displacements but with higher resolution. We found that the surface deformation is dominated by horizontal southward motion and vertical uplift and subsidence, with minor east-west deformation. In the north-south direction, the whole deformation area reaches at least 150 × 150 km with a maximum displacement of ~1.5 m. In the vertical direction, two areas, including uplift in the south and subsidence in the north, are mapped with a peak displacement of 1.5 and −1.0 m, respectively. East-west deformation presented a four-quadrant distribution with a maximum displacement of ~0.6 m. Complex thrusting movement occurred on the seismogenic fault; overall, there was southward push motion and wave-shaped fold motion.

Impacts of Topographic Relief and Crustal Heterogeneity on Coseismic Deformation and Inversions for Fault Geometry and Slip: A Case Study of the 2015 Gorkha Earthquake in the Central Himalayan Arc

AbstractFault source models inverted from surface displacement measurements are a common tool to contextualize the seismotectonic significance of earthquakes. However, these models commonly invoke a simplified homogeneous elastic half‐space (flat Earth) description of Earth, which may bias the resulting fault geometries and slip distributions in the presence of spatially varying Earth's elastic structure and topography. Here, we developed both forward and inverse three‐dimensional finite‐element models with planar faults to systematically assess the impacts of topography, crustal elastic structure, and fault geometry on surface deformation and earthquake source inversions, with a focus on the 2015 Gorkha, Nepal earthquake. Our forward models with fixed fault slip confirm the impacts of topography and crustal heterogeneity on surface deformation. These impacts, however, contribute only maximally ∼10% of the total surface displacement, and the fault depth and dip dominantly control the coseismic deformation for the Gorkha case. When using homogeneous half‐space models to invert the synthetic displacement fields generated by forward finite‐element models, we find that ignoring crustal heterogeneity primarily biases inferred dip angle, while ignoring relief primarily biases inferred fault depth. Our inversions based on finite‐element models suggest that topography and crustal heterogeneity introduce negligible bias on recovering the Gorkha line of sight observations. Fault dip angle and depth can systematically trade off with slip area and slip magnitude, regardless of the presence of relief and crustal heterogeneities. Taken together, our findings highlight the importance of fault geometry on inverted fault kinematics with geodetic observations in the central Himalayan arc.

Tectonic regimes and stress patterns in the Vrancea Seismic Zone: Insights into intermediate-depth earthquake nests in locked collisional settings

Earthquake nests are anomalous clusters of seismicity located far from active collisional systems in intraplate, locked suture zones, or the deep part of relic subducted slabs, challenging classic earthquake generation mechanism theories. The Vrancea Seismic Zone in Romania is such an upper-mantle seismic nest located in the SE Carpathians, releasing the largest strain in continental Europe. To better understand earthquake generation and the relationship with lithospheric deformation, we estimate earthquake source parameters in Vrancea and surrounding regions between 2014 and 2020, and determine the stress field via focal mechanism inversion and unsupervised machine learning. In the crustal domain, maximum horizontal stress is in agreement with surface fault kinematics and GPS-derived S-SE trending horizontal plate velocities relative to Eurasia, implying that tectonic stress is vertically coherent on a crustal scale. The stress regime changes from transpression beneath the orogen to transtension towards the foreland where movement is accommodated along major crustal faults, and tension further away from the epicentre, in the Moesian Platform and the North Dobrogea Orogen. Inside the seismogenic body vertical tension and an overall compressive regime dominates, implying that vertical elongation may be the driving mechanism for brittle failure and that stress is transmitted along the sinking slab to the surface. However, the retrieved stress ratios are low: ~0.2 for mantle earthquakes Mw>4 and ~0.4 for Mw<4, challenging the brittle failure assumption. Increased pore fluid pressure has been shown to lower stress ratios, implying that dehydration embrittlement may contribute to generating intermediate-depth seismicity in the Vrancea slab. Comparisons with seismic tomography and anisotropy studies show excellent correlations between maximum horizontal stress directions, possible slab strike orientation, and seismic anisotropy, especially below ~130km depth, suggesting ambient mantle flow may also promote in-slab stress build-up and seismic potential.

Tall building performance‐based seismic design using SCEC broadband platform site‐specific ground motion simulations

AbstractThe scarcity of strong ground motion records presents a challenge for making reliable performance assessments of tall buildings whose seismic design is controlled by large‐magnitude and close‐distance earthquakes. This challenge can be addressed using broadband ground‐motion simulation methods to generate records with site‐specific characteristics of large‐magnitude events. In this paper, simulated site‐specific earthquake seismograms, developed through a related project that was organized through the Southern California Earthquake Center (SCEC) Ground Motion Simulation Validation (GMSV) Technical Activity Group, are used for nonlinear response history analyses of two archetype tall buildings for sites in San Francisco, Los Angeles, and San Bernardino. The SCEC GMSV team created the seismograms using the Broadband Platform (BBP) simulations for five site‐specific earthquake scenarios. The two buildings are evaluated using nonlinear dynamic analyses under comparable record suites selected from the simulated BBP catalog and recorded motions from the NGA‐West database. The collapse risks and structural response demands (maximum story drift ratio, peak floor acceleration, and maximum story shear) under the BBP and NGA suites are compared. In general, this study finds that use of the BBP simulations resolves concerns about estimation biases in structural response analysis which are caused by ground motion scaling, unrealistic spectral shapes, and overconservative spectral variations. While there are remaining concerns that strong coherence in some kinematic fault rupture models may lead to an overestimation of velocity pulse effects in the BBP simulations, the simulations are shown to generally yield realistic pulse‐like features of near‐fault ground motion records.

Deformation patterns and potential active movements of the Fansipan mountain range, northern Vietnam

Located in northern Vietnam, the Fansipan mountain range is the highest topography in the Indochina area. Until recently, there has been limited research regarding the tectonic deformation of the Fansipan mountain range and whether there are notable surface ruptures or active faults in the area. This study provides the first insight into the deformation patterns and potential active movements of the Fansipan mountain range, and may improve our understanding of the overall tectonic activities in northern Vietnam. Our observations from ASTER 30-m DEM show a symmetrical mountain form in the north and an asymmetrical form in the south. The analysis of river profiles indicates similar patterns on both sides in the north and different patterns in the south with short and steep rivers on the SW side and long and gentle rivers on the NE side. The results of the normalized steepness index (ksn) also show higher values on the SW side of the south part than the values from the other sides. These results suggest a spatial variation in rock uplift patterns of the Fansipan mountain range. Notably, the mountain front of the SW side of the southern Fansipan mountain range is associated with the Phong Tho-Nam Pia normal fault, suggesting that the normal faulting activity likely played an important role in tectonic uplift of this high mountain range. Our investigation of the stress field using fault kinematics indicates that the Fansipan mountain range and its surrounding areas are undergoing an inhomogeneous mixture of strike-slip and normal faulting. It is proposed that the strike-slip and normal motions alternated because of a permutation of σ1/σ2 under the same extensional stress regime of approximately NE–SW σ3. This kinematic pattern may effectively control the recent tectonic movements in northern Vietnam.

Oblique Right‐Lateral Faulting Along the Northern Margin of the Ili Basin in the Northern Tian Shan, Northwest China

AbstractThe quantification of the geometry and kinematics of the boundary faults of an active orogenic belt is key to exploring its deformation pattern. The Kashihe fault (KSHF), which bounds the northern margin of the Ili Basin and is more than 400 km long, is a WNW‐striking fault in the northern Tian Shan. Although the KSHF displays active faulting and is the seismogenic fault of the 1812 Ms 8 Nilka earthquake, the quantitative slip rate and its role in regional strain accommodation have not been reported. Here, we quantify the late Quaternary activity of the KSHF based on high‐resolution remote sensing image interpretations and detailed field investigations. Six field observation sites along a ~270 km active fault in the Chinese Tian Shan indicate that the KSHF is characterized by dextral strike‐slip faulting and N‐S thrusting. Based on the surveying of offset geomorphic surfaces with an unmanned drone and the dating of late Quaternary sediments using optically stimulated luminescence (OSL) and radiocarbon methods, we estimated a late Quaternary right‐lateral strike‐slip rate across the fault of 2.39 ± 0.55 mm/yr and a shortening rate of 0.62 ± 0.30 mm/yr. Analysis of field investigations and fault section exposing indicated that a young paleoearthquake event occurred on the western segment of the KSHF. Active tectonics around the Ili Basin imply that the rigid Ili block extrudes westward along its boundary strike‐slip faults and rotates counterclockwise. We propose that this block rotation driven by dextral faulting accommodates regional N‐S convergence and sinistral shearing.

Fault kinematics and paleostress analysis using seismic data: A case study from the Archinsk field, West Siberian Basin, Russia

We present a methodology to determine the stress field based on the analysis of 3D seismic reflection data without additional information from wells. It involves the analysis of seismic horizons that were folded before the analyzed fault system. Fold hinges-faults intersections provide piercing points and fault slip vectors, which can be processed in the same way as slickenlines. Four seismic horizons and 51 faults in the Archinsk field, West Siberian Basin, were analyzed. The resulting fault-slip dataset is heterogeneous and has 126 slip vectors, corresponding to normal and strike-slip faulting. A normal stress regime with stress ratio (Φ) of 0.5 and a NE-trending minimum principal stress (σ3) is identified for the Late Triassic-Early Jurassic. A strike-slip stress regime with stress ratio (Φ) of 0.3, NW- and NE-trending maximum (σ1) and minimum principal stresses (σ3) corresponds to the present-day stress field.

Tectonics of the Dead Sea Fault Driving the July 2018 Seismic Swarm in the Sea of Galilee (Lake Kinneret), Israel

AbstractNorthern Israel was struck during July 2018 by a ML4.4 earthquake followed by a seismic sequence that lasted about 30 days. This seismic sequence occurred in the center of a temporary seismic network deployed around the Sea of Galilee (Lake Kinneret). The network was installed to investigate the regional kinematics of the Dead Sea Fault, which is a major transform fault running N‐S for more than 1,000 km. The data allowed us to develop a local velocity model for the Sea of Galilee. We relocated more than 600 earthquakes and calculated 27 focal mechanisms pointing out a complex kinematic setting, possibly controlled by fluids at depth. The seismic sequence developed along a NNW‐striking direction and it is bounded to the east by the N‐striking Dead Sea fault. Hypocenter depths range between 6 and 13 km. Directions of the principal stress tensors suggest a transtentional deformation, in agreement with the overall kinematics of the region.We analyze and discuss our data set to investigate mechanisms that potentially triggered the observed seismic swarm, including exacerbated ground water pumping proposed by previous authors. We suggest that the seismic sequence is driven by the dissipation of the elastic load that accumulated in this region.

Step-over fault zones controlling geothermal fluid-flow and travertine formation (Denizli Basin, Turkey)

In the Honalilar area (Denizli Basin, Turkey), the occurrence of banded Ca-carbonate veins and travertine deposits, represented by a dismantled fissure ridge-type depositional system, are the evidence of a middle-late Pleistocene exhumed, shallow, hydrothermal system. Their occurrence offers the best opportunity to: (i) reconstruct the fluid paths from the underground to the palaeo-surface, and (ii) analyse the role of fault zones in controlling the permeability and fluids circulation. Permeability developed in overstepping regional scale normal faults, with a slight left-lateral oblique-slip component. At the surface, faults favored the localization and development of a fissure ridge-type travertine deposit. At depth, the root of the hydrothermal system consists of W-E oriented fractures filled of up to 6.5 m thick Ca-carbonate veins, developed in a high dilatation zone. It corresponds to the step-over determined by the oblique-slip kinematics of the NW-striking main faults. The high dilatation step-over zone contrasted the progressive sealing induced by the concomitant Ca-carbonate deposition within the fractures, thus favoring permeability maintenance and fluids circulation for at least 200 ka. This evidence adds key inputs for predicting permeable volumes during geothermal exploration in areas affected by extensional tectonics. The main NW-oriented faults remained active even after the hydrothermal fluid flow, causing the dismantlement and progressive exhumation of the upper part of the hydrothermal system.

Geometry and kinematics of the Baza Fault (central Betic Cordillera, South Spain): insights into its seismic potential

The geometry and kinematics of active faults have a significant impact on their seismic potential. In this work, a structural characterization of the active Baza Fault (central Betic Cordillera, southern Spain) combining surface and subsurface data is presented. Two sectors are defined based on their surface geometry: a northern sector striking N–S to NNW–SSE with a narrow damage zone and a southern sector striking NW–SE with a wide damage zone. A kinematic analysis shows pure normal fault kinematics along most of the fault. Geometric differences between the northern and southern sectors are caused by i) a heterogeneous basement controlling the fault geometry at depth and in the cover; ii) different orientations of the Baza Fault in the basement with respect to the regional extension direction and iii) interaction with other active faults. We use this structural characterization to analyse the segmentation of the Baza Fault. According to segmentation criteria, the entire Baza Fault should be considered a single fault seismogenic segment. Consequently, the seismic potential of the fault is defined for a complete rupture. Magnitude for the Mmax event is calculated using several scale relationships, obtaining values ranging between Mw 6.6 and Mw 7.1. Recurrence times range between approximately 2,000 and 2,200 years for Mmax events and between 5,300 and 5,400 years for palaeo-events. A geodetic scenario modelled for an Mmax event of Mw 6.7 shows permanent vertical displacements of more than 0.40m and an overall WSW–ENE extension during entire ruptures of the Baza Fault.

Evaluation of the Plio-Quaternary tectonic stress regime from fault kinematic analysis in the lake Van Basin (Eastern Anatolia)

We focus on the Neogene–Quaternary tectonic evolution of the Lake Van Basin located within the Turkish-Iranian Plateau. To better understand the complex tectonic history of the region and determine the paleostress patterns, we investigate and report on the geometric, structural, and kinematic characteristics of the Basin based on field observations of fault-slip orientations which are classified according to radiometric ages of the basin stratigraphy.The analysis of large-scale structures and fault kinematics indicate that three different deformation phases prevailed in the Lake Van Basin during the Neogene-Quaternary periods. Phase 1 is characterized by NW-SE extension and NE-SW contraction that gave rise to the development of strike-slip faults with thrust or normal components during the late Miocene, deforming the fluvial sediments which expose at east/northeast of the Basin. Phase 2 is characterized in fluvial and lake deposits of the Middle Pleistocene, deformed by dominant contraction stress regime effective along NW-SE direction. The late Pleistocene tectonic regime (Phase 3) consists of transpressional deformation that develops under NNW-SSE compression and ENE-WSW extension. According to our analysis, the present-day deformation pattern of the Lake Van Basin is dominated by compression at east, while at the northern part is transtensional.

Upper Kama potassium salt deposit tectonic scheme based on physical modeling results and geological and geophysical data

Introduction. The territory of the Upper Kama potassium salt deposit (UKPSD) which has been actively developed since 1932, is characterized by abnormal technogenic overload on the geological environment. This load destroys the natural balance of the geological environment, the restoration of which is accompanied by hazardous dynamic events, from rockbursts to induced earthquakes of various magnitudes. Dynamic conditions of UKPSD is determined by many factors, among which a significant role is played by tectonic factors. Tectonic structure in the form of tectonic features or criteria (or other equal conditions) are taken into account first of all when fulfilling dynamic zoning of UKPSD territory and predicting the areas of possible manifestation of dynamic events. As soon as structural and tectonic elements of geological environment are characterized by similarity and hierarchy, it is advisable to study the tectonics of the deposit at various scales by corresponding geological and geophysical methods applying physical simulation data. Research methodology. Tectonic structures similarity and hierarchy (with a crack analysed as a copy of a fault), determined the two-stage technique of studying the tectonic structure of UKPSD territory. At the first stage, according to physical simulation data, areas influenced by the deep faults enclosing the Solikamsk depression and UKPSD were reconstructed. At the second stage, analyses was carried out of UKPSD fault strike azimuths determined by geological and geophysical methods. Research results. According to the results of the physical simulation, the dimensions of the area of dynamic impact of all faults enclosing the Solikamsk depression taking into account their kinematic type, and strikes and kinematics of faults within the zone of each fault were determined. Statistical analysis was carried out together with rose diagrams of strike azimuths of faults in the foundation and faults in UKPSD depth determined according to the results of magnetic field local anomalies interpretation, geomorphological data, satellite and aerial images. Summary. Tectonic scheme of UKPSD is not random. It is determined basically by the kinematics of deep faults enclosing UKPSD, and the tectonics of the foundation.

Mesozoic–Cenozoic Evolution and the Fault Kinematics of the Nurol Depression (Southern West Siberian Basin)

New fault kinematics data within the Archinsk field located in the Nurol depression (south part of the West Siberian Basin) are obtained by structural analysis of the 3D seismic reflection data. Two stages of fault formation in the Mesozoic–Cenozoic period are distinguished. The first stage is characterized by a normal stress regime with a NE-trending minimum principal stress and corresponds to Triassic rifting. The second stage is characterized by Cenozoic reactivation of the pre-existing faults and the formation of new, predominantly strike-slip faults, with submeridionally and sublatitudinally trending minimum and maximum principal stresses, respectively.

Morphology, structure, and kinematics of the San Clemente and Catalina faults based on high-resolution marine geophysical data, southern California Inner Continental Borderland (USA)

AbstractCatalina Basin, located within the southern California Inner Continental Borderland (ICB), United States, is traversed by two active submerged fault systems that are part of the broader North America–Pacific plate boundary: the San Clemente fault (along with a prominent splay, the Kimki fault) and the Catalina fault. Previous studies have suggested that the San Clemente fault (SCF) may be accommodating up to half of the ∼8 mm/yr right-lateral slip distributed across the ICB between San Clemente Island and the mainland coast, and that the Catalina fault (CF) acts as a significant restraining bend in the larger transform system. Here, we provide new high-resolution geophysical constraints on the seabed morphology, deformation history, and kinematics of the active faults in and on the margins of Catalina Basin. We significantly revise SCF mapping and describe a discrete releasing bend that corresponds with lows in gravity and magnetic anomalies, as well as a connection between the SCF and the Santa Cruz fault to the north. Subsurface seismic-reflection data show evidence for a vertical SCF with significant lateral offsets, while the CF exhibits lesser cumulative deformation with a vertical component indicated by folding adjacent to the CF. Geodetic data are consistent with SCF right-lateral slip rates as high as ∼3.6 mm/yr and transpressional convergence of &amp;lt;1.5 mm/yr accommodated along the CF. The Quaternary strands of the SCF and CF consistently cut across Miocene and Pliocene structures, suggesting generation of basin and ridge morphology in a previous tectonic environment that has been overprinted by Quaternary transpression. Some inherited crustal fabrics, especially thinned crust and localized, relatively hard crustal blocks, appear to have had a strong influence on the geometry of the main trace of the SCF, whereas inherited faults and other structures (e.g., the Catalina Ridge) appear to have minimal influence on the geometry of active faults in the ICB.

The 29 March 2017 Yuzhno-Ozernovskoe Kamchatka Earthquake: Fault Activity in An Extension of the East Kamchatka Fault Zone as Constrained by InSAR Observations

ABSTRACTRecent earthquakes off the northeastern Kamchatka coast reveal that this region is seismically active, although details of the locations and complexity of the fault system are lacking. The northern part of Kamchatka has poor coverage by permanent seismic stations and ground geodetic instruments. Here, we exploit the Differential Interferometric Synthetic Aperture Radar (DInSAR) technique to characterize the fault geometry and kinematics associated with the 29 March 2017 Mw 6.6 Yuzhno-Ozernovskoe earthquake. The aim is to contribute to identifying the active fault branches and to better understanding the complex tectonic regime in this region using the DInSAR technique, which has never before been applied to the analysis of coseismic offsets in Kamchatka.We produced coseismic deformation maps using Advanced Land Observation Satellite-2 ascending and descending and Sentinel-1A descending Synthetic Aperture Radar (SAR) scenes and detected a predominant uplift up to 20 cm and a westward motion of approximately 7 cm near the shoreline. We jointly inverted the three geodetic datasets using elastic half-space fault modeling to retrieve source geometry and fault kinematics. The best-fit solution for the nonlinear inversion suggests a north–west-dipping oblique reverse fault with right-lateral rupture.The model fault geometry is not only generally consistent with the seismic data but also reveals that a hitherto unknown fault was ruptured. The identified fault structure is interpreted as the northern extension of the east Kamchatka fault zone, implying that the region is more complex than previously thought. Important implications arise for the presence of unknown faults at the edges of subduction zones that can generate earthquakes with magnitudes greater than Mw 6.