Current Stress Regime Research Articles

Structural controls on hydrothermal fluid flow in a carbonate geothermal reservoir: Insights from giant carbonate veins in western Germany

This study examines the impact of polyphase tectonics on the development of structurally controlled hydrothermal fluid pathways in carbonate geothermal reservoirs. Our case study focuses on hydrothermal carbonate veins and vein-filled faults in Devonian carbonates from the North Rhine-Westphalia region in western Germany, currently being explored as a potential low-enthalpy geothermal reservoir at depths of 4–5 km. These veins, which can be up to 20 m thick, are subvertical and strike NNW, N, or ESE. They exhibit pinch-and-swell undulating geometries, faulted vein-wall contacts, and occasional fillings of hydrothermal breccias. Vein-filled normal faults show hybrid shear-dilatant openings, with fault tips characterized by horsetail vein terminations. The textures, orientations, and age of the veins suggest their formation at low confining pressures and at depths < 2 km during the Post-Variscan East-West extension. Orthogonal North- and East-striking strike slip faults, inherited from the Variscan orogeny, were likely reactivated during post-Variscan extension, with a significant dilatant component that formed the observed veins. In the Ruhr Basin, the dilation tendency analysis indicates that NNW-striking veins or joints are optimally oriented for re-opening under the current strike-slip stress regime, characterized by NNW-trending maximum horizontal stress. The intersections of fractures may currently create moderately SSE-plunging linear zones of enhanced fluid flow. The main uncertainty regards the presence of similar structures at geothermal reservoir depths of ∼4–5 km in the Middle Devonian carbonates underneath the Ruhr Basin. As the study veins are likely to have formed at depths <2 km, the existence of analogous dilatant conduits at greater depths remains speculative. Eventually, we propose that zones characterized by open discontinuities and channelized fluid flow in carbonate geothermal reservoir in strike-slip tectonic settings can be: (a) dilational jogs between overlapping strike-slip faults, (b) bends along faults, and (c) strike-slip fault terminations with horsetail extensional structures. These zones can also be prone to enhanced karstification.

Regional and field assessments of potentials for geological storage of CO2: A case study of the Niger Delta Basin, Nigeria

The Niger Delta, as an actively producing oil and gas region has potential to develop into a new CO2 geological storage hub. Criteria for screening basins for Carbon Capture and Storage (CCS) was used in combination with 3D seismic data and well information to assess the basin's potential in this contribution. It is shown here that the presence of excellent reservoir-seal pair, very large basin size, suitable reservoir depth, matured oil and gas fields, moderate faulting intensity, availability of giant hydrocarbon fields and being a passive margin generally makes the Niger Delta basin excellent environment for CCS. High resolution 3D seismic dataset and well information from case study areas enabled identification of potential reservoir, traps and seals. Geomechanical analyses have shown that slip tendency is generally low while fracture stability is high, which indicates that the study area is stable in the current stress regime.

Hydrogeomorphological observations from Thenmala and Thenmala south fault, India

Achankovil shear zone is a North West-South East (NW-SE) oriented Precambrian structure of South India. Present work identified evidences of two faults (trending NW-SE) in the southern most end of this shear zone. They are Thenmala fault and Thenmala south Fault. This study is an attempt to understand the structural control of these NW-SE structures over the drainage development of the study area, based on geomorphological evidences and field data. Morphometric analysis of the drainage basins clearly indicate that basins located near NW-SE structures shows more anomalies. This anomalies in the vicinity of lineaments and faults indicate their influence over the drainage development. Observed brittle faults evidences with numerous slip planes from the south eastern end of the study area also support this argument. Morphometric evidences in association with brittle fault observations suggest that Achankovil shear zone may be week and reacting to the current stress regime.

Long-lived crustal damage zones associated with fault intersections in the high Andes of Central Chile

Long-lived, high-angle fault systems constitute high-permeability zones that can localize the upward flow of hydrothermal fluids and magma throughout the upper crust. Intersections of these types of structures can develop complex interference patterns, which constitute volumes of damaged rock (networks of small-scale faults and fractures) where permeability may be significantly enhanced. This is relevant for understanding regional-scale structural controls on the emplacement of hydrothermal mineral deposits and volcanic centers, and also on the distribution of areas of active upper-crustal seismicity. In the high Andes of central Chile, regional-scale geophysical (magnetic, gravimetric, seismic) and structural datasets demonstrate that the architecture of this Andean segment is defined by NW- and NE-striking fault systems, oblique to the N-S trend of the magmatic arc. Fault systems with the same orientations are well developed in the basement of the Andes. The intersections of conjugate arc-oblique faults constitute the site of emplacement of Neogene intrusive complexes and giant porphyry Cu-Mo deposits, and define the location of major clusters of upper-crustal earthquakes and active volcanic centers, suggesting that these fault systems are still being reactivated under the current stress regime. A proper identification of one-dimensional, lithospheric-scale high-permeability zones located at the intersections of high-angle, arc-transverse fault systems could be the key to understanding problems such as the structural controls on magmatic and hydrothermal activity and the patterns of upper-crustal seismicity in the high Andes and similar orogenic belts

Where was the 31 October 1895 Charleston, Missouri, Earthquake?

AbstractWe revisit the magnitude and location of the 31 October 1895 Charleston, Missouri, earthquake, which is widely regarded to be the most recent Mw 6 or greater earthquake in the central United States. Although a study by Bakun et al. (2003) concluded that this earthquake was located in southern Illinois, more than 100 km north of the traditionally inferred location near Charleston, Missouri, our analysis of exhaustively compiled macroseismic data supports the traditionally inferred location, with a preferred magnitude of Mw≈5.8 and a preferred magnitude range of 5.4–6.1. Our preferred magnitude is derived from comparisons with intensity distributions from the 1925 Mw 6.2 Charlevoix, the 1944 Mw 5.8 Massena, and the 1968 Mw 5.3 southern Illinois earthquakes, macroseismic data of which we also revisited in this study. Based on the distribution of liquefaction, reports of damage, and early aftershocks, we also explore possible rupture scenarios for the 1895 earthquake. Our preferred scenario involves unilateral rupture to the northeast on a (reactivated) northeast‐striking fault (or faults) coinciding with structures associated with the western limb of the Reelfoot rift, with an epicenter south‐southeast of Charleston, Missouri. Our results support the conclusion that within the Reelfoot rift, elevated seismic hazard is not restricted to the New Madrid seismic zone as conventionally defined but continues into the Charleston region in southeastern Missouri, where faults associated with the western edge of the Reelfoot rift appear favorably oriented for failure in the current stress regime.

Tectonic Evolution of the Southern Negros Geothermal Field and Implications for the Development of Fractured Geothermal Systems

Fluid flow pathway characterisation is critical to geothermal exploration and exploitation. In fractured geothermal reservoirs, it requires a good understanding of the structural evolution together with the fracture distribution and fluid flow properties. A fieldwork-based approach has been used to evaluate the potential fracture permeability characteristics of a typical high-temperature geothermal reservoir in the Southern Negros Geothermal Field, Philippines. This is a liquid-dominated resource hosted in the andesitic Quaternary Cuernos de Negros Volcano, Negros Island. Fieldwork reveals two main fracture groups based on fault rock characteristics, alteration type, relative age of deformation, and associated thermal manifestation, with the youngest fractures mainly related to the development of the current geothermal system. Fault kinematics, cross-cutting relationships, and palaeostress analysis suggest at least two distinct deformation events under changing stress fields since probably the Pliocene. We propose that this deformation history was influenced by the development of the Cuernos de Negros Volcano and the northward propagation of a major neotectonic structure located to the northwest, the Yupisan Fault. A combined slip and dilation tendency analysis of the mapped faults indicates that NW-SE structures should be particularly promising drilling targets under the inferred current stress regime, consistent with drilling results. However, existing boreholes also suggest that NE–SW structures can act as effective channels for geothermal fluids. Our observations suggest that these features were initiated as the dominant features in the older kinematic system and have then been reactivated at the present day.

New insights on structures and active faults in northeastern Tunisia (Utica-Mateur region) from a gravity analysis: Geodynamic implications

Gravity data were analyzed in conjunction with earthquake, seismic reflection, and geological data to investigate the upper crustal structure of the Utica-Mateur region of northeastern Tunisia and relate this structure to the current tectonic environment of northern Tunisia. To accomplish this goal, gravity anomaly maps were constructed using isostatic gravity residual methods, match-filtering to create residual anomalies, and horizontal gravity gradients. Additionally, the depths to the major density contrasts were determined using a 2D power spectrum analysis and Euler deconvolution and 2D forward modeling. The residual gravity anomalies interpreted in conjunction with gradient determined lineaments indicate that there are several gravity maxima related to uplifted regions bounded by lineaments that trend mainly to northeast- and northwest. Based on the Euler deconvolution analysis, the majority of these lineaments are located at shallow depths (<6 km) and can be related to the seismic activity of the region. Correlating these newly imaged lineaments, uplifts and subsiding areas with seismicity and focal mechanism studies, a new structural map is proposed for the Utica-Mateur region. The majority of the region can be interpreted by uplifts and subsiding (pull apart basins) areas bounded by strike-slip faults that contain compressional and extensional stress components. This stress regime is thought to be caused by the reactivation of older structures by the current compressional stress regime due to the convergent of Africa and Eurasia and active rifting of the Sicily basin. However, the proposed recent segmentation of a northeast-retreating subducting slab under Africa that caused a major lithospheric discontinuity to the south of the Utica-Mateur region added second and third order tectonic variations. These variations modified the stress regime which caused the formation of strike-slip faults and the gravity analysis indicates that the entire Utica-Mateur region is still affected by this stress field change.

A new global database to improve predictions of permeability distribution in crystalline rocks at site scale

AbstractA comprehensive worldwide permeability data set has been compiled consisting of 29,000 in situ permeabilities from 221 publications and reports and delineating the permeability distribution in crystalline rocks into depths of 2000 meters below ground surface (mbgs). We analyze the influence of technical factors (measurement method, scale effects, preferential sampling, and hydraulic anisotropy) and geological factors (lithology, current stress regime, current seismotectonic activity, and long‐term tectonogeological history) on the permeability distribution with depth, by using regression analysis and k‐means clustering. The influence of preferential sampling and hydraulic anisotropy are negligible. A scale dependency is observed based on calculated rock test volumes equaling 0.6 orders of magnitude of permeability change per order of magnitude of rock volume tested. Based on the entire data set, permeability decreases as log(k) = −1.5 × log(z) − 16.3 with permeability k (m2) and positively increasing depth z (km), and depth is the main factor driving the permeability distribution. The permeability variance is about 2 orders of magnitude at all depths, presumably representing permeability variations around brittle fault zones. Permeability and specific yield/storage exhibit similar depth trends. While in the upper 200 mbgs fracture flow varies between confined and unconfined, we observe confined fracture and matrix flow below about 600 mbgs depth. The most important geological factors are current seismotectonic activity (determined by peak ground acceleration) and long‐term tectonogeological history (determined by geological province). The impact of lithology is less important. Based on the regression coefficients derived for all the geological key factors, permeability ranges of crystalline rocks at site scale can be predicted. First tests with independent data sets are promising.

Fault zones in layered carbonate successions: from field data to stress field models

We present a field-study based workflow to develop 3D-numerical models on local stress fields within fault zones hosted in layered rocks at reservoir depths. As an example we use the carbonate successions of the Upper Muschelkalk (Middle Triassic) in the Upper Rhine Graben, Southwest Germany, that form a reservoir for deep geothermal energy. Steps of the workflow include (A) characterization of fault-zone units and mechanical layering, (B) estimations of rock mechanical properties and (C) assumptions on the in situ stress regime. Results of 3D-numerical models of fault-zone local stress fields at reservoir depth of 2900 m show pronounced differences depending on (1) fault-zone orientation, (2) impact of maximum horizontal stress SH in the given stress regime (normal faulting, strike-slip faulting or transitional normal to strike-slip faulting), (3) fault-zone scale and (4) contrast in mechanical properties. Soft fault damage zones and fault cores trending at a minor angle to SH (0°–30°) concentrate less stress than comparable units at higher angles to SH (60°–90°), in particular in the strike-slip regime. The impact of mechanical layering increases with horizontal compression. This may result, for example, in formation of barriers to fracture propagation and thus lower probability of forming well-interconnected fracture networks necessary for fluid flow in reservoirs. Comparisons to estimated fault-zone stress states such as dilation and slip tendencies, show that their prediction in the study area is difficult because of the current transitional stress regime (normal to strike-slip faulting) and, in addition, varying orientations of SH.

Styles of neotectonic fault reactivation within a formerly extended continental margin, North West Shelf, Australia

We have investigated the locations and patterns of neotectonic deformation in the Carnarvon basin along the Mesozoic rifted margin of Western Australia to evaluate the characteristics of post-Neogene tectonic reactivation. Geological, geophysical, geotechnical, and bathymetric data demonstrate that preferentially oriented rift-era structures have been reactivated under the current neotectonic stress regime. The most recent pulse of neotectonic reactivation initiated during the Plio-Pleistocene (4.0 to 1.8 million years ago) and is ongoing. Reactivated structures in the region demonstrate a variety of styles of deformation consistent with dextral-transpression. Structural styles include both positive and negative flower structures, restraining and releasing bends, and hourglass structures. Barrow Island lies within a broad kinematic restraining bend that appears to warp the MIS 5e marine terrace on the island. Fold reconstructions of Neogene strata on the Cape Range and Barrow anticlines yield uplift rates consistent with uplift rates determined from folded late Pleistocene units in the Cape region. Although tectonic rates are low compared to interplate settings, evidence for active tectonic deformation precludes this part of the Australian plate from being classified as a Stable Continental Region.

Seismic reflection imaging of Quaternary faulting offshore the southeastern Korean Peninsula

The Yangsan Fault System (YFS) is a dominating tectonic structure in the southeastern part of the Korean Peninsula. The YFS consists of NNE-striking dextral strike-slip faults that are traced to the southeastern coast of the Korean Peninsula. We acquired high-resolution seismic profiles offshore the southeastern Korean Peninsula to investigate how the YFS extends offshore and constrain the age of fault activity using stratigraphic interpretation. The seismic profiles image near-vertical faults trending NE to NNE that constitute a fault zone similar to a duplex structure at a releasing bend of a right-lateral strike-slip fault. The faults are interpreted as an offshore extension of the Ilgwang fault that is a member of the YFS. Stratigraphic interpretation of seismic profiles indicates that the offshore faults were activated repeatedly in the Pliocene and Quaternary. The right-lateral activity of the Ilgwang fault is consistent with the current stress regime in and around the southeastern Korean Peninsula that dictates the P-axis direction in the E-W or ENE-WSW since the Pliocene.

Identification of a suspected Quaternary fault in eastern Korea: Proposal for a paleoseismic research procedure for the mapping of active faults in Korea

In terms of seismic hazard in the Korean Peninsula, the occurrence of destructive earthquakes has long been overlooked because of no serious modern instrumental seismicity and lack of historical earthquake records of large earthquakes. In recent years, although the importance and uses of paleoseismological studies has significantly increased in seismic hazard assessments of critical facilities, there is still a huge lack of paleoseismological data to improve our knowledge for Korean active tectonics and relevant seismic hazards. In this study, we identified and characterized a suspected Quaternary fault in the eastern part of the Korea Peninsula based on lineament analyses, field observations, and trench surveys. We focus on a prominent lineament around the northern part of the previously reported, but not sufficiently studied, Maeup Fault. Firstly, a potential fault lineament is recognized by geomorphic expressions in a mountainous area from satellite and digital elevation model (DEM)-generated images. Then, fault-related geomorphic and hydrologic features, such as disconnected drainages, sag ponds, and asymmetric water leaking out on an artificial ditch, were observed along the lineament in the field studies. Finally, the existence of the fault is confirmed by an exposure of a 2.5m wide fault core in trench surveys. The internal structures of the fault core (i.e., slip surfaces, slickenlines, and S-C fabrics) indicate that the fault evolved via a series of slip events under a variety of tectonic settings, probably leading up to the current stress regime sustained during Quaternary. Thus our results suggest that the newly identified fault could be a Quaternary fault, and hence it is necessary to perform more paleoseismic investigations around the study region. This case study emphasizes the importance of the careful interpretation of tectonic landforms and fault zone structures in the study of active faults, and proposes a suitable research procedure for the identification of active faults in Korea.

Paleo stress contribution to fault and natural fracture distribution in the Cooper Basin

The contribution of the unconventional reservoirs to the global oil and gas production made it important to address the main factors that control high production from these reservoirs. Hydraulic fracturing that intersect natural fractures results in a high stimulated rock volume and high production. Over a decade of effort to use elastic dislocation and different types of restoration to predict fracture network didn't succeed fully in addressing this factor.We used image log fractures and fault network within an iterative boundary element method (iBEM3D) to predict the paleo-tectonic events and the fracture network in the Cooper Basin. The methodology was able to predict only the major tectonic events that occurred after the deposition of the Cooper Basin sediments and contributed to the formation of the natural fractures. As the methodology does not include fault elastic properties, fracture orientations near the faults showed unrealistic results and should not be considered as indicative for the actual natural fractures.The main trend of the Cooper Basin fractures was attributed to post Triassic inter-seismic relaxation after major tectonic compressional events, which resulted in a normal fault stress regime. However, the current day stress regime is believed to be also a major factor in forming some of the natural fractures. Hunter Bowen orogeny in the Late Triassic contributed less to the existing fractures. Whereas, Cainozoic compressional forces played no role in the formation of the Cooper Basin natural fractures.

The Utica Shale and gas play in southern Quebec: Geological and hydrogeological syntheses and methodological approaches to groundwater risk evaluation

The risk of groundwater contamination from shale gas exploration and development is a major societal concern, especially in populated areas where groundwater is an essential source of drinking water and for agricultural or industrial use. Since groundwater decontamination is difficult, or nearly impossible, it is essential to evaluate exploration and production conditions that would prevent or at least minimize risks of groundwater contamination. The current consensus in recent literature is that these risks are primarily related to engineering issues, including casing integrity and surface activities, such as truck traffic (equipment and fluid haulage), waste management (mainly drill cuttings), and water storage and treatment when hydraulic fracturing is utilized. Concerns have also been raised with respect to groundwater contamination that could result from potential fracture or fault interconnections between the shale unit and surficial aquifers, which would allow fracturing fluids and methane to reach the surface away from the wellbore. Despite the fact that groundwater resources are relatively well characterized in some regions, there is currently no recognized method to evaluate the vulnerability or risks to aquifers resulting from hydrocarbon industry operations carried out at great depths.This paper focuses on the Utica Shale of the St. Lawrence Platform (Quebec), where an environmental study aiming to evaluate potential risks for aquifers related to shale gas development has been initiated. To provide the context of these research efforts, this paper describes the regional tectono-stratigraphic evolution and current stress regime of the Cambrian–Ordovician St. Lawrence Platform, as well as the Utica Shale internal stratigraphy, mineralogy and thermal maturation. Then, the hydrogeological context of the St. Lawrence Platform is discussed. Finally, the methodology for this environmental study, based on geological, geophysical, geomechanical, hydrogeological and geochemical data, is presented.

Implications of 2007’s Earthquake Activity in Eğirdir Lake (SW Anatolia) Based on Moment Tensor Solutions and Inversion of Stress State

We analyzed the waveforms of the small- to moderate-sized earthquakes that took place in the northern part of the inner Isparta Angle (IA) to retrieve their source parameters and combine these results with the focal mechanism solutions of the larger events that occurred in 2007 in Egirdir Lake at the apex of IA. In total, source mechanisms of 20 earthquakes within the magnitude range 3.5 < M < 5.0 were calculated using a regional moment tensor inversion technique. The inversion of the focal mechanisms yields an extensional regime with a NNE–SSW (N38°E) trending σ3 axis. Inversion results are related to a mainly WNW–ESE oriented normal fault beneath Egirdir Lake. The R value of a NNE–SSW extensional regime is 0.562 showing a triaxial stress state in the region. The current stress regime results from complex subduction processes such as slab pull, slab break-off, roll-back and/or retreating mechanism along the Hellenic and Cyprus arcs and the southwestward extrusion of the Anatolian block since the early Pliocene.

Are there any active faults within the Lepontine dome (central Alps)?

Abstract In metamorphic chain areas characterized by low seismicity, the evidence of neotectonic activity is generally very poor. However, direct evidences of seismogenic faults are reported hereafter in the Lepontine dome (Central Alps) considered in the literature as tectonically quiescent. Identification of aligned cluster of microseismic events guided morphotectonic researches. The latter revealed clear clues of recent faulting, i.e. marked scarps, perturbation of the drainage system or shift of terminal moraines. Thus, thanks to combination of seismological, geological and morphological data, we accurately locate four seismogenic faults and determine precisely their kinematic from fault-stria data and focal mechanisms. Three roughly NW-SE seismogenic dextral-normal faults were evidenced: the first close to the Simplon fault zone, the second in the middle northern part of the dome and the third one to the north of Bellinzona. They are part of a regional Riedel-shear zone system linked to the Insubric line. Dextral strike-slip component increases when strike of fault planes approaches the E-W orientation (corresponding to pure strike-slip) and respectively normal component increases when strike of fault planes is close to NW-SE. The second system highlighted corresponds to WSW-ENE normal faults mainly distributed on the whole northern flank of the dome along a zone of 10 km wide. They are roughly parallel to the Rhône and Bedretto valleys and exploit pre-existing basement fabric. These data coherent at all scales provide new constraints on the current stress regime going on in the Lepontine Dome and could have implications for future seismic hazard studies in the broader area.

Significance of brittle deformation in the footwall of the Alpine Fault, New Zealand: Smithy Creek Fault zone

The Smithy Creek Fault represents a rare exposure of a brittle fault zone within Australian Plate rocks that constitute the footwall of the Alpine Fault zone in Westland, New Zealand. Outcrop mapping and paleostress analysis of the Smithy Creek Fault were conducted to characterize deformation and mineralization in the footwall of the nearby Alpine Fault, and the timing of these processes relative to the modern tectonic regime. While unfavorably oriented, the dextral oblique Smithy Creek thrust has kinematics compatible with slip in the current stress regime and offsets a basement unconformity beneath Holocene glaciofluvial sediments. A greater than 100 m wide damage zone and more than 8 m wide, extensively fractured fault core are consistent with total displacement on the kilometer scale. Based on our observations we propose that an asymmetric damage zone containing quartz–carbonate–chlorite–epidote veins is focused in the footwall. Damage zone asymmetry likely resulted from the fact that the hanging wall was mostly deformed at greater depth than the footwall, rather than resulting from material contrasts across the fault plane. Kinematic inversions on mineralized fractures within the damage zone suggest veins formed in the current stress regime, from fluids comparable to those now circulating in the footwall. The Smithy Creek Fault zone is therefore a rare exhumed example of the modern footwall hydrothermal system, and of a structure actively accommodating footwall deformation near the Alpine Fault zone. Two significantly less mature, subvertical faults having narrow (20 cm or less) damage zones and similar orientations to nearby strike-slip segments of the Alpine Fault crosscut the mineralized zone at Smithy Creek. We envisage that hydrothermal mineralization strengthened the fault core, causing it to widen as later slip was partitioned into the (now) weaker surrounding damage zone. With progressive alteration, formation of favorably oriented faults became preferable to reactivation of the existing structure.

The role of stress history on the flow of fluids through fractures

AbstractUnderstanding flow along fractures and faults is of importance to the performance assessment (PA) of a geological disposal facility (GDF) for radioactive waste. Flow can occur along pre-existing fractures in the host-rock or along fractures created during the construction of the GDF within the excavation damage zone (EDZ). The complex fracture network will have a range of orientations and will exist within a complex stress regime. Critical stress theory suggests that fractures close to localized shear failure are critically stressed and therefore most conductive to fluid flow. Analysis of fault geometry and stress conditions at Sellafield has revealed that no features were found to be, or even close to being, classified as critically stressed, despite some being conductive. In order to understand the underlying reasons why non-critically stressed fractures were conductive a series of laboratory experiments were performed. A bespoke angled shear rig (ASR) was built in order to study the relationship between fluid flow (water and gas) through a fracture surface as a function of normal load. Fluid flow reduced with an increase in normal load, as expected. During unloading considerable hysteresis was seen in flow and shear stress. Fracture flow was only partially recovered for water injection, whereas gas flow increased remarkably during unloading. The ratio of shear stress to normal stress seems to control the fluid flow properties during the unloading stage of the experiment demonstrating its significance in fracture flow. The exhumation of the Sellafield area during the Palaeogene–Neogene resulted in considerable stress relaxation and in fractures becoming non-critically stressed. The hysteresis in shear stress during uplift has resulted in faults remaining, or becoming, conductive. The field and laboratory observations illustrate that understanding the stress-history of a fractured rock mass is essential, and a mere understanding of the current stress regime is insufficient to estimate the flow characteristics of present-day fractures.

LiDAR-Assisted Identification of an Active Fault near Truckee, California

Abstract We use high-resolution (1.5–2.4 points/m 2 ) bare-earth airborne Light Detection and Ranging (LiDAR) imagery to identify, map, constrain, and visualize fault-related geomorphology in densely vegetated terrain surrounding Martis Creek Dam near Truckee, California. Bare-earth LiDAR imagery reveals a previously unrecognized and apparently youthful right-lateral strike-slip fault that exhibits laterally continuous tectonic geomorphic features over a 35-km-long zone. If these interpretations are correct, the fault, herein named the Polaris fault, may represent a significant seismic hazard to the greater Truckee–Lake Tahoe and Reno–Carson City regions. Three-dimensional modeling of an offset late Quaternary terrace riser indicates a minimum tectonic slip rate of 0.4±0.1 mm/yr. Mapped fault patterns are fairly typical of regional patterns elsewhere in the northern Walker Lane and are in strong coherence with moderate magnitude historical seismicity of the immediate area, as well as the current regional stress regime. Based on a range of surface-rupture lengths and depths to the base of the seismogenic zone, we estimate a maximum earthquake magnitude ( M ) for the Polaris fault to be between 6.4 and 6.9.

Tectonic control over active volcanism at a range of scales: Case of the Rungwe Volcanic Province, SW Tanzania; and hazard implications

The volcano–tectonic architecture of the Rungwe Volcanic Province in SW Tanzania, part of the East African Rift System, was studied with integrated remote sensing imagery. A Shuttle Radar Topography Mission Digital Elevation Model was draped with geo-referenced geological and topographical maps and air photos. The entire RVP region was inspected systematically for tectonic lineaments and volcanic vents. Tectonic lineaments show two distinct directions, NW–SE and NNE–SSW, consistent with the idea of a current stress regime of local NE–SW compression. We find that there is tectonic control on the regional location for at least two of the three major volcanoes as well as for local distribution of eruptive vents on each of these three volcanoes. Field data show that major volcano instability events occurred in the Holocene for Ngozi caldera and Rungwe. These instability events are possibly associated with the faults controlling the location of both volcanoes. This study highlights the need for monitoring RVP tectonic and volcanic activity.