Geodetic Studies Research Articles

Power function of $${\varvec{F}}-$$ distribution: revisiting its computation and solution for geodetic studies

Power function of $${\varvec{F}}-$$ distribution: revisiting its computation and solution for geodetic studies

Estimating and Analyzing The Stability of Brazilian Gnss Stations for Tectonic Studies

The detailed study of stresses and strains is fundamental for geophysical and geodetic studies, enabling the development of plate motion models, geodynamic processes and several proposals. GNSS positioning has been used to estimate these stresses and strains. However, for the accuracy required, it is necessary a rigorous assessment of the behavior of GNSS stations and their position time series. This paper aims to analyze the influence of the different types of geodetic monuments present in the Brazilian GNSS Continuous Monitoring Network by estimating and characterizing noise in the time series and investigating variables that can affect the stability of the stations to establish criteria for using this data in tectonic and geodynamic studies. The evaluation of 119 GNSS stations throughout Brazil indicates the significant presence of random walk noise in some of these stations, detected by analyzing the magnitude of the noise and the spectral index. It was found that the stations with unstable monuments have been observed for at least eight years and are mostly in coastal areas or under the influence of large watercourses.

Geodetic constraints on three-component motion of the Ordos block (China) and their implications for lithospheric dynamics

Abstract The Ordos block is a rigid portion of the North China Craton lying within the India-Eurasia collision zone that experiences little internal deformation, but is surrounded by active faulting, extensional grabens, and seismicity. In the surrounding region, geodetic studies have imaged complex crustal deformation, while seismic studies have suggested that the lithosphere is encountering regional modification by mantle convection. The Ordos block thus presents a valuable opportunity to compare seismic and geodetic constraints and investigate geodynamic processes affecting the region’s lithosphere. We here robustly image vertical land motion and horizontal strain rates using observations from the geographically extensive Global Navigation Satellite System and leveling networks in and around the Ordos block. Our results indicate that the Ordos block uplifts with some lateral variability at 0.5–2.0 mm/yr. In the northeastern Ordos block and Datong volcanic area, the crustal uplift rates are 2.0–4.0 mm/yr on average, much faster than those elsewhere on the block. We correct for non-tectonic vertical motion from surface hydrological loading and glacial isostatic adjustment, finding that these do not explain the vertical rate anomalies. Horizontal crustal extension and uplift are accompanied by a pattern of crustal contraction at the Datong volcanic field. Additionally, we find uplift west of and subsidence east of the Qinling Orogenic Belt, which are inconsistent with eastward crustal extrusion along it, suggesting instead a negligible migration of crustal materials especially to the east of 106°E. Comparing the geodetic measurements to evidence from seismic velocity anomalies and numerical simulation, we argue that the motions are consistent with lithospheric re-equilibration resulting from the heterogeneous thinning of the lithosphere by convective mantle upwelling and radial flow as well as shortening from the India-Eurasia collision.

Three‐Dimensional Electrical Resistivity Structure Beneath a Strain Concentration Area in the Back‐Arc Side of the Northeastern Japan Arc

AbstractIntraplate earthquakes occur more frequently in the Japanese islands than in other regions. Large intraplate earthquakes in the island arc preferentially occur in strain concentration zones detected by geological and geodetic studies. Crustal heterogeneity plays a crucial role in generating large intraplate earthquakes and strain concentrations. Thus, we elucidated the crustal heterogeneities beneath a strain concentration area on the back‐arc side of the northeastern Japan Arc based on electrical resistivity, which is sensitive to weak zones in the crust. By deploying wideband magnetotelluric surveys, we revealed the three‐dimensional electrical resistivity structure in the crust, suggesting the coexistence of two different types of strain‐concentration mechanisms in the strain‐concentration area. The shallow conductive layers and lower‐crustal conductors appear to act as low‐elastic‐modulus and low‐viscosity areas, respectively, and are responsible for the strain concentration. We found shallow and lower‐crustal conductors in the strain concentration zone revealed by geological studies. Those conductive areas are considered to act as mechanically weak zones and cause stress loading on the brittle pars of pre‐existing faults, resulting in large intraplate earthquakes. The resultant earthquakes presumably contribute to strain accumulation on a geological timescale. In addition, a spatial correlation between the epicenters of large intraplate earthquakes and edges of lower‐crustal conductors implies the contribution of the fluids in the lower crust to the generation of large earthquakes. We also identified vertical conductors ranging from the lower crust to Quaternary volcanoes, which may indicate trans‐crustal magmatic systems under these volcanoes.

Геодезичне забезпечення відновлення багатофункціонального комплексу ТРЦ «Нікольський» в місті Харків

The application of geodetic surveys is a vital aspect of assessing the destruction of buildings as a result of Russian armed aggression. The study compares Ukrainian and foreign research methods, highlights their advantages and disadvantages. The legislative framework for geodetic support for restoration of buildings on the territory of Ukraine has been analyzed. As international experience has shown, geodetic surveys are an effective tool for assessing the destruction of buildings as a result of military operations. The study is aimed at evaluating the structural integrity on the example of the shopping and entertainment center “Nikolskyi” in the city of Kharkiv. Geodetic methods used to assess structural damage are reviewed, and an overview of the results of these damage assessments is provided. It is investigated how geodetic surveys can be used to assess structural damage in buildings. The purpose of the article is the study of geodetic works and methods of geodetic support for restoration works of the shopping center building. To achieve the goal, the following tasks were performed: analysis of previous experience in this area; the choice of the method of geodetic provision of restoration works; presenting the results of geodetic measurements; interpretation of the obtained results. Method. To obtain research results, special methods are used: constructive and substantive analysis – for the formation of research directions; analytical methods – to process the results of the shooting; mathematical modeling – to determine the amount of destruction and damage to the building. A Leica Geosystems TCRP 1205 tacheometer and other geodetic equipment were used in the study to assess the structural integrity of the shopping center. The combination of geodetic measurements with the use of tacheometers is an important area of application of tacheometers in similar tasks. In addition, classical surveys, using total station geodetic measurements, were performed in conjunction with an automatic strain monitoring system to ensure the accuracy and reliability of the structural integrity assessment. Therefore, using the specified devices, it is possible to accurately measure and analyze the structural integrity of the shopping center. Scientific novelty and practical significance. The scientific novelty of the conducted research consists in the creation of modern approaches to geodetic support for restoration works of buildings that were destroyed as a result of military operations. Original methods of geodetic surveying and a modern instrument base from NVP “Navigation and Geodetic Center” are applied. The proposed geodetic studies demonstrate the effectiveness of using geodetic measurements to assess structural damage to buildings. Deformation values obtained with the help of geodetic studies helped determine the volumes and technology of restoration, which provides important information for engineering works. It has been shown that the use of electronic tacheometer measurements is a reliable and accurate means of determining damage levels and locations even in complex fracture locations. The Leica TCRP 1205 total station accurately measures angles and distances in a reflection-free mode to achieve the highest accuracy of work. In addition, the measuring technology that was applied at the object of research can be used for geodetic research during the detection of shifts and deformations of building structures. Future research could explore the application of geodetic measurements to other types of buildings or structures damaged by military action. In general, the studies carried out reinforce the potential and importance of geodetic measurements for restoration programs that are planned and will be planned in the near future.

Disagreements in Geodetically Inferred Strain Rates in the Western US With Stress Orientations and Geologic Moment Rates

AbstractI employ an elasticity‐based method to invert a geodetically derived surface velocity field in the western US using for present‐day surface strain rate fields with uncertainties. The method uses distributed body forces in a thin elastic sheet and allows for discontinuities in velocity across creeping faults using the solution for dislocations in a thin elastic plate. I compare the strain rate fields with previously published stress orientations and moment rates from geological slip rate data and previous geodetic studies. Geologic and geodetic moment rates are calculated using slip rate and off‐fault strain rates from the 2023 US National Seismic Hazard Model (NSHM) deformation models. I find that computed total geodetic moment rates are higher than NSHM summed moment rates on faults for all regions of the western US except the highest deforming rate regions including the Western Transverse Ranges and the northern and southern San Andreas Fault (SAF) system in California. Computed geodetic moment rates are comparable to the moment rates derived from the geodetically based NSHM deformation models in all regions. I find systematic differences in orientations of maximum horizontal shortening rate and maximum horizontal compressive stress in the Pacific Northwest region and along much of the SAF system. In the Pacific Northwest, the maximum horizontal stress orientations are rotated counterclockwise 40–90° relative to the maximum horizontal strain rate directions. Along the SAF system, the maximum horizontal stresses are rotated systematically 25–40° clockwise (closer to fault normal) relative to the strain rates.

Detectability analysis of very low frequency earthquakes: methods and application in Nankai using F-net and DONET broad-band seismometers

SUMMARY For a more quantitative discussion of slow earthquake activity, we evaluated the detectable limits of very low frequency earthquakes (VLFEs), which are seismic slow earthquakes observed in very low-frequency (< 0.05 Hz) bands in the Nankai subduction zone. We performed numerical simulations using a local 3-D model and used the observed noise level of permanent broad-band seismometers. First, we investigated the effects of the source-time functions on the maximum amplitudes of the VLFE signals at a certain station. The maximum amplitudes of the VLFE signals were controlled by the VLFE moment rate. The detectable limit of VLFEs at each source location can be defined as the lowest moment rate of detectable VLFEs, which radiate signals larger than the noise levels of any component at ≥ 3 stations. For inland seismometers only, the detectable limits of VLFEs at deep (30–40 km) and shallow (≤ 10 km) depths were 1012–1012.3 and 1012.7 N·m s−1, respectively. Due to the geometrical spreading of VLFE signals and large noise levels in horizontal components, offshore seismometers improved the detectability of shallow VLFEs in regions where seismometers were densely deployed. Based on our detectability and published catalogues, shallow slow earthquakes are less active south-southwest off the Kii Peninsula, where geodetic studies expect mechanical coupling.

РЕЗУЛЬТАТЫ МОНИТОРИНГА СОВРЕМЕННЫХ ДЕФОРМАЦИОННЫХ ПРОЦЕССОВ МЕТОДАМИ ВЫСОКОТОЧНОЙ ГЕОДЕЗИИ НА ЯМБУРГСКОМ ГЕОДИНАМИЧЕСКОМ ПОЛИГОНЕ

The article presents the results of surveying and geodetic studies of modern deformation processes on the territory of the Yamburg oil and gas condensate field. The technogenic influence of the development on the formation of vertical shifts of observation points of the geodynamic polygon has been established. It is determined that the greatest subsidence is confined to the areas of maximum sampling and falling reservoir pressures in the area of the combined contours of the Cenomanian and Neocomian. It is shown that there is a tendency of subsidence of the earth's surface over the mined area of the deposit. It was revealed that a comparative analysis of the results of geodynamic monitoring: satellite observations, geological and commercial indicators of the field development allowed to determine the local subsidence zone in the northern part of the field. The results of the research can be useful for surveying services of oil and gas fields when performing geodynamic monitoring.

Geodetic slip rate partitioning in the central Anninghe and Daliangshan faults: Effects of fault geometry, elastic heterogeneity, and viscoelastic rheology

Geodetic measurements can be employed to estimate the secular slip rates and locking depths of crustal faults, two key parameters which influence assessment of long-term seismic hazard presented by a fault. However, this process requires making assumptions about the rheological properties of the Earth's crust and lithosphere, as well as the fault geometry at depth. Previous geodetic studies have inferred widely varying slip rates and locking depths for the central Xianshuihe-Xiaojiang Fault System, located along the southeastern margin of the Tibetan plateau. In this study, we use updated GNSS measurements, including 13 new velocities, to explore the effects of assumed rheology and fault geometry on the inferred slip rates and locking depths of the subparallel Anninghe (ANH) and Daliangshan (DLS) faults in this region. We demonstrate that only models taking into account the viscoelastic relaxation of the lower crust can resolve the apparent discrepancies. Models assuming a fully elastic rheology suggest very deep locking depths (∼35 km) and a lower slip rate on the ANH fault (∼5 mm/yr) than the DLS fault (∼7 mm/yr). Neither the relative slip rates nor the locking depths agree with seismic or geologic observations. We also consider models assuming a heterogeneous elastic rheology, but find they are indistinguishable from the homogeneous models. Modifying the fault geometry can impact the relative slip rates of the two faults but does not produce a reasonable locking depth either. In contrast, viscoelastic models accounting for seismic cycle effects indicate a faster ANH slip rate (∼5–7 mm/yr), a slower DLS rate (∼4–5 mm/yr), and a shallower locking depth for both faults (∼18 km), all of which are more consistent with independent seismic and geological observations. Our study suggests that steady long-term motion on these faults is modulated by long-lasting viscoelastic effects over a relatively broad region.

Unveiling the pre-eruptive seismic series of the La Palma 2021 eruption: Insights through a fully automated analysis

We have analyzed the seismic series that preceded the La Palma 2021 eruption using a fully automated workflow based on Deep Learning. A new seismic catalog has been obtained that contains twice the number of events as the original manual catalog. The new catalog consists of 5059 absolute locations obtained using a non-linear location method and a 3D velocity model of the island, as well as relative locations by means of double differences method. Our enhanced catalog contains detailed features of seismic migration through the crust. We differentiate the sequence into three stages leading up to the eruption onset using independent seismic parameters: inter-event time variation coefficient, b-value spatial distribution, hypocentral migration and magnitude distribution. Our analysis identifies two magmatic intrusions: The first migrates from the center of the Cumbre Vieja area to the west coast of the island (stage 1), where it stagnates. After two days of seismic quiescence (stage 2), a second intrusion begins near the center of the island and rises to the surface leading to the eruption (stage 3). These results were further validated by GNSS observations and previous geodetic studies. Our findings highlight the usefulness of this type of automated methodology, offering a real-time and accurate response during intense seismic episodes.

Predictive Modelling of Land Subsidence Due to Groundwater Level Decline in Gedebage District, Bandung, Indonesia

The Gedebage district in Bandung city has experienced a vast physical development in recent years. Previous geodetic studies showed that the area undergoes high-rate land subsidence. The subsurface soil of the Gedebage area has remarkably high compressibility, void ratio, and water content. A thick sequence of soft organic clay of 20-27 m exists, making the area prone to subside. As the district continues to develop, it is important to predict the future rate of land subsidence in the area. This paper aims to analyze the contribution of groundwater exploitation to the land subsidence rate. A combination of 1-dimensional Terzaghi consolidation analytical analysis and numerical modeling was employed in this study. Groundwater level data up to 2015 was used, and hydrostatic condition was assumed to occur in 1986. Results show that the Gedebage area has subsided as much as 161 cm since 1986. Modeling results are consistent with geodetic survey results. It is predicted that the land subsidence will slow down in the next 40 years, provided that the groundwater level remains stable.

Crustal structure of the Lazufre volcanic complex and the Southern Puna from 3-D inversion of magnetotelluric data: Implications for surface uplift and evidence for melt storage and hydrothermal fluids

Abstract The Central Andes are unique in the global system of subduction zones in that a significant, high-altitude plateau has formed above a subduction zone. In this region, both subduction and the associated magmatism have been shown to vary in both space and time. Geophysical data have been invaluable in determining the subsurface structure of this region. Extensive seismic studies have determined the regional-scale distribution of partial melt in the crust and upper mantle. Magnetotelluric studies have been effective in providing independent constraints on the quantity and composition of partial melt in the crust and upper mantle. Geodetic studies have shown that a small number of volcanic centers exhibit persistent, long-term uplift that may indicate the formation of plutons or future eruptions. This paper describes a detailed study of the Southern Puna using magnetotelluric (MT) data. This region is located at the southern limit of the Central Andes in a region where a recent transition from flat-slab subduction to normal subduction has caused an increase in magmatism, in addition to hypothesized lithospheric delamination. It is also a region where an extensive zone adjacent to the volcanic arc is undergoing surface uplift, located near Volcán Lastarria and Cordon del Azufre (collectively called Lazufre). The main goals of the work are to define the crustal structure and to investigate processes that may cause surface uplift of relatively large regions not associated with active volcanism. As part of the PLUTONS project, MT data were collected on an east-west transect (approximately along 25°S) that extended across the Southern Puna, from Lazufre to north of Cerro Galan. The data were combined with previously collected MT data around Lazufre and inverted to give a 3-D resistivity model of the crust. The low resistivity of the crust resulted in limited sensitivity to mantle structure. A number of major crustal conductors were detected and included (1) a mid-crustal conductor extending eastward from the volcanic arc as far as the Salar de Antofalla; (2) an upper- to mid-crustal conductor located north of Cerro Galan; and (3) a conductor that rises westward from (1) and terminates directly beneath the region of surface uplift at Lazufre. These conductors are broadly coincident with the location of crustal low shear-wave anomalies. The conductive features were interpreted to be due to zones of partial melt stored in the crust, and petrological data were used to estimate melt fractions. Below Lazufre, it is likely that aqueous fluids contribute to the high conductivity, which is observed within the depth range of the inflation source, giving evidence that the surface uplift may be associated with both magmatic and hydrothermal processes.

Determining the relationship between the slope and directional distribution of the UAV point cloud and the accuracy of various IDW interpolation

Inverse Distance Weighted (IDW) based interpolation method is also widely used in earth science studies. In the classical IDW method, the directional distribution of the reference points around the point to be estimated within the critical circle and the slope differences are not taken into consideration. On the other hand, in the IDW-based method developed by Shepard, the ratio of the distances of the reference points within the critical circle to the critical circle radius (r), the anisotropy and the slope differences are taken into consideration. In this study, the results of the classical IDW method and Shepard method were compared to increase the accuracy of interpolation produced from UAV data. A software has been developed to make these comparisons in more detail. The classical IDW and Shepard based interpolation methods used in this software takes into consideration the anisotropy, the slope differences and the ratio of the distances to the critical circle radius. In this study, UAV flights were performed in three different study areas with different topographic features and 3D point cloud data were obtained in order to make detailed analyzes. Using developed software, data from three different study areas have been tested and the results from different Shepard interpolation models have been discussed. The major contribution of this paper is in evaluation of various IDW options when applied to UAV point data. As a result, especially in geodetic studies form UAV data, it was observed that the results improved with 11% to 37% by using the Shepard method with the suitable power parameter value considering the directional distribution of the reference points in the critical circle and the slope differences.

Reconstructed Centennial Mass Balance Change for Golubin Glacier, Northern Tien Shan

Mass balance measurements for Golubin glacier in Northern Tien Shan, Kyrgyzstan, have been discontinuous over the last century, with significant data gaps. We provide a unique over 100-year-long mass balance series on daily resolution. We applied a temperature index model calibrated with glaciological measurements and validated with secular mass balances derived from independent length change observations. A comparison with other recent geodetic studies reveals good agreement. Golubin lost −0.16 ± 0.45 m w.e. a−1 from 1900/1901 to 2020/2021. From the long-term mass balance time series, we identify a shift to a more negative/less positive regime with time, with a steepening of the ablation and accumulation gradients, especially for the past two decades. We observe a parallel shift of the mass balance gradient accompanied by a rotation of the ablation gradient due to increased ablation at the glacier tongue and accumulation above the equilibrium line altitude. This tendency is believed to intensify in the future, affecting glaciers’ mass balance sensitivity to changes in atmospheric conditions and year-to-year variability and resulting in irregular melt water release feeding the rivers that provide water to Bishkek. These kinds of datasets are sparse for Tien Shan and, yet, indispensable to enhancing our understanding of glacier changes in High Mountain Asia.

Tuz Mağaralarında Sırt Çantası LiDAR Sisteminin 3B Model Üretiminde Kullanılması; Tuzluca, Iğdır Örneği

Caves have an important place in world history. In addition to the protective and flavoring properties of salt, the conclusion that it can be an alternative treatment for various diseases has increased the importance of salt caves. In this study, a 3D model of the salt cave located in the Tuzluca District of Iğdır Province, which was opened for the purpose of health tourism, was created using the backpack LiDAR system. The fact that the backpack LiDAR system is supported by a fast, flexible use and SLAM algorithm has increased its use in confined spaces such as caves. The created model has been converted into a geodetic coordinate system. It is observed that the location and transformation accuracy of the model are within the usable accuracy in geodetic studies. With this study, it was determined that the backpack LiDAR system can be used in cave studies.

Spatially focused erosion in the High Himalaya and the geometry of the Main Himalayan Thrust in Central Nepal (85°E) from thermo-kinematic modeling of thermochronological data in the Gyirong region (southern China)

The subsurface structure of the Himalaya is dominated by the seismically active Main Himalayan Thrust fault, which accommodates about half of the plate convergence between India and Asia. In Central Nepal, geological, geophysical, and geodetic studies indicate that the Main Himalayan Thrust has a flat-ramp-flat geometry, which causes cooling, erosion, and exhumation of rocks to be faster above the mid-crustal ramp than above the adjacent upper and lower flats. However, in the northern High Himalaya the ramp geometry, in particular its width and depth are not well resolved. To place further constraints on the northward extent and depth of the ramp, we present for the first time low-temperature thermochronological data and U-Pb zircon ages from the Gyirong region, China (northern High Himalaya). Our zircon U-Pb data show that the protolith of the High Himalayan orthogneisses is 478 ± 4 Ma old, and was intruded by a large leucogranite at 19.5 ± 0.7 Ma. The Pliocene-Quaternary cooling of the study area is constrained by apatite fission track ages and apatite and zircon (U-Th)/He ages between ~5 Ma and ~ 0.5 Ma, which show a marked trend of southward-younging ages. Together with published cooling ages from Nepal farther south, the ages define a U-shaped pattern across the Main Himalayan Thrust, with ages increasing to the north and south from a minimum in the High Himalaya. A thermo-kinematic model, in which the geometry of the mid-crustal ramp was varied, explains the age data and suggests that the ramp has a dip of ~22°N. Compared to previous models, our new ages require that the ramp has a greater width (~55 km) and reaches a greater depth (~34 km) below the northern High Himalaya. Still farther north, the fault is presumably developed as a gently-dipping ductile shear zone, which forms the prominent reflector visible in seismic reflection data.

Взаимосвязь геомеханики и недропользования с позиций законодательного определения термина «Недра»

The article presents a historical overview of the development of Geomechanics as a science in the re-search school of the Institute of Mining of the Ural Branch of the Russian Academy of Sciences. A par-ticular attention is given to research into the stress-and-strain state of the rock mass and its changes in the course of operating the mining facilities, which plays a crucial role in securing the stability of struc-tures, mining safety, and prevention of major accidents. To ensure the safety of mining, a complex of research methods is used, including theoretical studies, physical and computer modeling, geophysical sensing of rock masses, ground-surface and satellite geodetic studies of the deformation processes. Geomechanical studies carried out at the Institute of Mining helped to gain new insights into the struc-ture of rock masses, variability of the stress-and-strain state, its mosaic structure as determined by the self-organization process within hierarchical block mass, to reveal the sources of emergencies and cat-astrophic events in mining. Current geomechanical research at the Institute is dedicated to the development of a scientific approach and execution of territory zoning using the criterion of technogenic and natural disasters in mining, studying regularities in the self-organization processes within the rock mass, development of technology to select favorable locations for hazardous and critical mining facili-ties. A special role is played by the prediction of possible changes in the stressandstrain state over time. The Geomechanics Department of the Institute of Mining uses field studies of the rock mass structure, geodetic studies of its mobility, remote sensing using satellite interferometry, and computer simulation of the properties and processes that take place within the rock mass.

The Effect of the 3‐D Structure on Strain Accumulation and the Interseismic Behavior Along the North Anatolian Fault in the Sea of Marmara

AbstractThe 150‐km seismic gap in the Sea of Marmara is the longest section of the North Anatolian Fault that has not ruptured in the last century. Recent geodetic studies suggest that the interseismic coupling along the Main Marmara Fault (MMF) is heterogeneous with locked and creeping segments. Alternatively, the MMF is fully locked, but the strain is localized asymmetrically around the fault due to the deep basins. In this study, we build a 3‐D model of the region, including the basins and the 3‐D fault geometry, to study the competing effects of deep basins and the interseismic locking distribution using the observed Global Navigation Satellite System velocities. We conclude that the basins along the fault localize the interseismic strain, leading to slightly deeper‐estimated locking depths. The on‐land data are too far to constrain the full interseismic coupling, especially in the Central Marmara. The Western Marmara is better resolved, where we infer a ∼50‐km creeping zone. The transition from the creeping to the locked behavior in Western Marmara is around the Ganos Bend. The creeping zone correlates well with a higher rate of diffuse seismicity and repeating earthquakes, implying that the seismicity could be an indicator of interseismic behavior. Variations of earthquake focal mechanisms and associated regional stresses are also consistent with compressional and dilatational quadrants due to the creeping segment. The significant thrust components observed in the 2019 Silivri earthquake sequence north of the MMF can also be explained by the compressional loading due to the interseismic creep further west.

Combined acoustical and seismic studies of Axial Seamount

The NSF Ocean Observatories Initiatives Regional Cabled Array at Axial Seamount provides a remarkable facility for sustained studies of an active submarine volcano. A local seismic network supports a real-time earthquake catalog and hydrophones monitor sounds in the water column. In April 2015, Axial Seamount erupted shortly after the cabled observatory came on line. The seismic record of brittle deformation in the summit caldera during the eruption is complemented by acoustic observations that tracked a dike propagating along the north rift using T phases and recorded both impulsive and continuous sound sources on the seafloor at the sites of erupting lava. Seafloor pressure gauges are presently documenting the reinflation of the volcano towards its next eruption and these geodetic studies would be enhanced by deploying a transponder network to support horizontal ranging. The availability of real-time data to detect and localize future eruptions will enable effective autonomous and ship-based responses to study how hydrothermal systems and their chemosynthetic biological communities respond to eruptions. The seismic and acoustic networks could also support studies of fin and blue whales to understand whether their distribution is modulated by the enhanced productivity associated with the presence of a hydrothermally active seamount.

Geophysical Constraints on the Crustal Architecture of the Transtensional Warm Springs Valley Fault Zone, Northern Walker Lane, Western Nevada, USA

AbstractThe Walker Lane is a zone of distributed transtension where normal faults are overprinted by strike‐slip motion. We use two newly acquired, high‐resolution seismic reflection profiles and a reprocessed Consortium for Continental Reflection Profiling (COCORP) deep crustal reflection profile to assess the subsurface geometry of the Holocene‐active, transtensional Warm Springs Valley fault zone (WSVFZ) near Reno, Nevada, USA. Our multiscale observations extend to 12 km depth and suggest that the WSVFZ is more complex in the subsurface than implied by late Pleistocene surface fault traces. Two 4‐km‐long high‐resolution profiles image to a depth of ∼2 km and reveal moderately dipping reflections and truncations, some of which project to mapped scarps formed in late Pleistocene surfaces. The shallow lines are collocated with COCORP profile NV 08 along ∼40°N latitude. Reanalysis of the COCORP data reveals previously unidentified coherent reflections to a depth of ∼12 km and a previously mapped ∼30° west‐dipping fault at 8–12 km. From these seismic profiles, the WSVFZ is not a simple, subvertical fault zone extending through the entire seismogenic crust. Instead, the reflections are consistent with a zone of steeply and moderately dipping faults that simplify and steepen with depth before intersecting a mid‐crustal, low‐angle (∼25–30°) fault. The complex fault geometry of the WSVFZ implies that crustal shear is accommodated by a mix of dipping and subvertical faults in the transtensional northern Walker Lane. If so, transtensional fault zones may present challenges to paleoseismic and geodetic studies and require careful treatment when included in seismic hazard analyses.