Regional Tectonic Stress Research Articles

Experiments on the evolution of laccolith morphology in plan-view

The ultimate shape of a laccolith is the result of competition between internal magmatic phenomena (e.g. overpressure and the process of solidification), and the state of the external host rock (e.g. thickness of the overburden, the presence of faults, and regional tectonic stresses). Intrusion morphology can be utilized as an inferential tool to better understand emplacement dynamics and history. One specific shape aspect rarely considered is the intrusion's ellipticity, which is the ratio of its long to short axes in plan view. Here, with a series of simple analog experiments that integrate the effects of flow along pre-existing fractures and solidification during emplacement, an assessment is performed of the existing models for formation of a laccolith's plan morphology; i.e. growth-dependent and feeder-dependent. The results of these experiments suggest that neither model fully captures the behavior of laccolith ellipticity evolution, and an updated model of formation that takes into account the control of the feeder dike, homogenization of overburden bending moments, and the processes involving solidification is presented. Furthermore, experimental results are compared with ellipticity measurements of natural laccoliths. There are proportionately more high ellipticity laccoliths in Nature than in experiments. This is interpreted as an induced morphological effect by magma viscosity, crustal heterogeneities, and/or incremental assembly.

Characterising the present-day stress regime of the Georgina Basin

ABSTRACTThe onshore Georgina Basin in northern Australia is prospective for unconventional hydrocarbons; however, like many frontier basins, it is underexplored. A well-connected hydraulic fracture network has been shown to be essential for the extraction of resources from the tight reservoirs that categorise unconventional plays, as they allow for economic flows of fluid from the reservoir to the well. One of the fundamental scientific questions regarding hydraulic stimulation within the sub-surface of sedimentary basins is the degree to which local and regional tectonic stresses act as a primary control on fracture propagation. As such, an understanding of present-day stresses has become increasingly important to modern petroleum exploration and production, particularly when considering unconventional hydrocarbon reservoirs. This study characterises the regional stress regime in the Georgina Basin using existing well data. Wellbore geophysical logs, including electrical resistivity image logs, and well tests from 31 petroleum and stratigraphic wells have been used to derive stress magnitudes and constrain horizontal stress orientations. Borehole failure features interpreted from wellbore image and caliper logs yield a maximum horizontal stress orientation of 044°N. Integration of density log data results in a vertical stress gradient of 24.6 MPa km–1. Leak-off and mini-fracture tests suggest that this is the minimum principal stress, as leak-off values are generally shown to be at or above the magnitude of vertical stress. The maximum horizontal stress gradient is calculated to be in the range of 31.3–53.9 MPa km–1. As such, a compressional stress regime favouring reverse/reverse–strike-slip faulting is interpreted for the Georgina Basin.

Tectonic stress field analysis of the northern part of the Kuril–Okhotsk region before the May 24, 2013 deep-focus earthquake

This paper presents the results of reconstruction of the modern tectonic stress field of the northern part of the Kuril–Okhotsk region prior to the May 24, 2013 deep-focus earthquake. This earthquake is the strongest deep-focus earthquake not only in the Okhotsk region but also in the world over the entire period of seismic observations. The tectonic stress field is reconstructed using the method of cataclastic analysis (MCA) of the earthquake source mechanism data. New data on the depth variations of regional tectonic stress field are obtained.

Focal Mechanism of Volcano-tectonic Earthquakes at Merapi Volcano, Indonesia

Merapi (2968 m), located in central Java, is one of the most active and dangerous volcanoes in Indonesia. The volcano has repeated episodes of dome growth and collapse, producing pyroclastic flows during historical time. Volcano-tectonic (VT) earthquakes have been classified into deep (VTA) and shallow one (VTB). Since August 2000, number of VT events (M=1.0-1.6) had increased, and pyroclastic flows have successively occurred from the middle of January, 2001. The focal zone vertically extends to about 4 km deep beneath the summit. VTA events are located at the depth 2.2-4.1 km and the VTB ones at the depth shallower than 1.3 km. An aseismic zone is observed around 1.3-2.2 km deep between the hypocenter zones of the two types of VT earthquakes, interpreted as shallow magma storage. Focal mechanism of VT events was estimated by using both polarity and amplitude of P-wave first motions at 4 seismic stations, assuming double couple mechanism and homogenous medium. Determined focal mechanisms for VTA events are of normal-fault types. VTA events might originate by increase in horizontal tension when magma rose up from deeper portion. Orientation of their T-axes is nearly horizontal in NEE-SWW direction which might be affected by the E-W regional tectonic stress. As for the VTB, normal fault types dominate the deep VTB zone, while at the shallow part, both reverse fault and normal fault types are originated. The pressure increases at shallow magma storage may cause generation of deep VTB events of normal fault types. As VTB events frequently originated, corresponding to increase of multiphase (MP) events which are related to growth of lava dome, shallow VTB events of reverse fault type might be generated by horizontal compression related to pressure decrease in magma conduit due to extrusion of lava and gases, and occasionally by pressure increase at the shallow part due to accumulation of magma or volcanic gases.

Short-lived eruptive episodes during the construction of a Na-alkalic basaltic field (Perşani Mountains, SE Transylvania, Romania)

The Persani Mts. basaltic field covers >176 km2 (~22 × 8 km) and is one of the youngest and biggest monogenetic volcanic fields in Southeastern Europe. It consists of 21 monogenetic volcanic centers, most of which were built on a basement of Miocene rhyolitic tuffs and Mesozoic sedimentary rocks. 40Ar/39Ar dating shows that the eruptions took place in five episodes: 1220, 1142, 1060, 800, and 683 ka. An additional undated episode at 1060–800 ka has been identified using volcanological observations. Initial phreatomagmatic activity was commonly followed by explosive Strombolian/Hawaiian phases that deposited agglutinated spatter around the vents along with massive-to-bedded unconsolidated scoria and lapilli. Some volcanoes lack evidence for magmatic explosive activity, while others lack evidence for the initial phreatomagmatic phase. During most eruptions, the final activity was the effusion of lava flows that in some cases deformed (or partially destroyed) the volcanic edifices. The erupted volumes varied greatly from one episode to other, without showing any pattern: the highest volumes are recorded in deposits from the third pulse (1060 ka). The volcanoes are located close to faults and always on their footwall blocks, and it is inferred that the regional tectonic stress regime controlled both the timing and spacing of volcanic activity in the volcanic field.

Partial reactivation of a huge deep-seated ancient rock slide: recognition, formation mechanism, and stability

Abstract. About 18 years ago, a large-scale discontinuous layer in properties and colour was found in the new Fengjie town at the shore of the Three Gorges Reservoir area in China. There are many resettled residents and buildings on the sloping area, the safety of which is potentially affected by this layer, so it has become the focus of attention. Before this study started there were two viewpoints regarding the origin of this layer. One was that is was from a huge ancient slide and the other was that is was from a fault graben. In order to find out how it was formed and to be able to carry out a stability analysis of the slope the authors have carried out a research program, including geological field investigations and mapping, a deep drilling hole, a geotechnical centrifuge model test, and a simulation analysis. The results of the research led to the conclusion that the layer is the sliding plane of a huge deep-seated ancient rock slide, which we called the Sanmashan landslide. An important argument for the conclusion is the recognition of a regional compressive tectonic stress field in this area, which cannot lead to the formation of a fault graben because it needs a tensional tectonic stress field. Moreover, numerous unique geological features, sliding marks, and other relics of the ancient slide have been discovered in the field. The formation process of the ancient slide could be repeated in a large geotechnical centrifuge model test. The test shows that a deformation and failure process of "creep–crack–cut" has occurred. The type of the ancient slide can be classified as a "successive rotational rock slide". Finally, the role of seepage in the stability of the Sanmashan landslide has been analysed. Our final conclusions are that, during rainfall and filling–drawdown cycles in the Three Gorges Reservoir, the Sanmashan landslide as a whole is dormant and stable and the secondary landslides in the toe area of the slope are presently stable but can be reactivated. This research provides an important basis for the remedial measures and land use planning in the new Fengjie town, and a well-documented case history for researchers worldwide.

Geostress tests and analysis of the Tibet Bangpu mining area

In this paper, importance of geostress in mining engineering and the development of geostress tests are stated. The basic principle of geostress measurement through stress relief method using bore strain gauge 36–2 is expounded. Through improvement on traditional test technology and technical equipment of bore strain gauge 36–2, the geostress of the Tibet Bangpu mining area, at an altitude of 4670 m, was successfully tested. This provides technical reference for the stress measurement in similar areas and provides an analysis basis for the nearly 1000 m high slope stability. Combined with field test results and a sequence of elastic modulus experiment results, the geostress was obtained and analysed. The thickness of the overlying strata is one of the main factors to influence stress in the mining area the value of the minimum principal stress. The maximum principal stress is 2.1 times the vertical stress when the thickness of the overlying strata is greater than 100 m. The regional tectonic stress of the Bangpu mining area is in a NE direction due to the Indian Ocean plate subducting beneath the Eurasian plate. The stereographic projection of the three-dimensional geostress test azimuth and the Tibet Bangpu mining area final design pit slope analysis the superiority and inferiority with the final pit slope’s stress state from the aspects of the geostress, indicate that 1# and 6# final pit slope trends almost perpendicular to the maximum principal stress. This is an undesirable force state and implies that monitoring and support while open-pit mining must be strengthened.

A secondary sludge flow hazard induced by shallow-source seismic activity in karst mining area, Guangxi, South China: localized karstification in anticline

On the 16th of June 2013, a small-magnitude, shallow-source seismic activity just occurred at a karst mining area. No serious ground damage occurred, but it induced a secondary geological hazard. The wastewater and sludge leaked from the mining water reservoir which caused a great economic loss and groundwater contamination through multilevel underground karst channels. The seismic swarm was located along the Youjiang fault, an active fault zone whose kinematics is controlled by the regional tectonic stress field with NW300° compression and NE30° extension. The tectonic fractures are sealed by calcite, and stylolites have permeabilities of less than 0.01 mD. The localized intensive karstification occurred at the core of Yalang anticline, which is the result of a local extension stress environment and hydrogeological conditions. The seismic activity in the study area is not strong enough to cause ground destruction, but did alter the flow dynamics of groundwater. The seismic activity may have caused a temporary high pressure fluid in the fault zone. The karst system blocked by sediments can be dredged by the fluid pressure. Then, the karstification of limestone massif could be re-activated.

Engineering and Tectonic Study of Rocks Discontinuities in the Proposed Abo-Hederya Quarry Site, Missan SE Iraq

A detailed field survey of discontinuity (fractures) was carried out in the proposed Abo-Hederya Quarry Site, 70 km east Missan city, south-east of Iraq, where Al-Mukdadiya Formation (Upper Miocene-Pliocene) is exposed. The discontinuity survey was carried out in 10 stations covering the study area. At each station notes were collected about beds (lithology, thickness and orientation) and discontinuities (orientation, density, spacing, persistence and aperture). The slope stability analysis suggests that there is no real hazard area that could affect the quarry in future. Tectonic analysis demonstrates that tension fractures are common in the study area, while shear fractures (okl, hko, hol and hkl) are the less. The maximum principal stress direction in the study area is N (15 - 40) E, which is compatible with the regional tectonic stress in the area.

Co-seismic and post-seismic effects of the Tohoku-Oki M W 9.0 earthquake in North and Northeast China

Using the US Geological Survey (USGS) finite fault model, the co-seismic horizontal displacement and horizontal principal stress field in North and Northeast China generated by the Tohoku-Oki M W 9.0 earthquake of March 11th, 2011, were retrieved by linear elastic finite element numerical simulation. On this basis, the static Coulomb failure stress variations of the main active faults and tectonic zones in North and Northeast China were calculated, and the triggering effect of the earthquake on seismicity in North and Northeast China was discussed. Results were as follows: (1) the co-seismic horizontal displacement field caused by the great earthquake was eastward in North China; the maximum value, which occurred in the Shandong Peninsula and north Jiangsu Province, was about 12 mm; and the values gradually decreased from east to west. The co-seismic horizontal displacement field in Northeast China was SE–SEE and the maximum value, which occurred in northeast Jilin Province, was about 30 mm. The simulated results for the co-seismic horizontal displacement field were in good agreement with GPS observational results. (2) The near-surface co-seismic maximum horizontal principal stress (ΔσHmax) was tensile stress ranging from 0 to 2.0 KPa. From Northeast China to North China, the direction gradually altered from NW to NWW to nearly EW to NEE. The co-seismic minimum horizontal principal stress (ΔσHmax) was compressive as well as tensile stress, with a magnitude of 0–0.75 KPa, which is approximately equal to zero. From Northeast China to North China, the direction gradually changed to NNW from NE to NNE to nearly NS. Although the co-seismic stress effect generated by the great earthquake had some effect on the present tectonic stress field of North and Northeast China, its influence was too slight to change the present framework of the regional tectonic stress field. (3) Coulomb failure stress variations on active fault zones in North and Northeast China mainly increased; however, the amount of increase was less than 1 KPa. The increases were largest in the middle and northeastern segments of the Tancheng–Lushan fault zone and the Mishan–Dunhua fault zone. The Tohoku-Oki Mw9.0 earthquake did have some triggering effect on seismic activity in North and Northeast China, but the effects were limited.

Active surface cracking in Aghajari Formation of the Azar oil field, Zagros, western Iran

A very rare case of deformation is described in which surface cracks are being developed in a period of few months over an area of ca. 55 km2 in the Late Miocene–Early Pliocene Lahbari Member of Aghajari Formation outcropped in the Azar oil field of western Iran. The cracks are unique because of their activity and their relation to regional tectonic stress field, and not to shallow local processes. The cracks are almost parallel to the NE–SW shortening direction deduced from local folds, and are of almost pure tensile nature. Strike-slip faulting in the area is also in kinematic concordance with the cracks, which show a NW–SE extension direction. Erodibility of the surface geological materials and their downwashing by surface water is affecting the surface morphology very quickly. It is suggested that movement of incompetent underlying Middle Miocene Gachsaran Formation on a lateral ramp of the Zagros Foredeep Fault, and regional active shortening of the sedimentary sequence are responsible for development of the cracks. Construction of the Mohr diagram predicts that maximum depth of the tensile cracks is ca. 220 m. Weak mechanical nature of the Lahbari Member and transient pore pressure are major contributing factors for the crack development. Study of these active cracks may help to better understand the process of active and past fracturing in foreland fold thrust belts.

CO2-rich inclusions in vein gold–copper mineralization of the Sarekoubu–Qiaxia District, southern Altaides, China: Implication for ore genesis

The Sarekoubu–Qiaxia area of the southern Altaides hosts a number of vein gold and copper deposits, in which a great number of carbonic fluid inclusions were found. For many years, the ore genesis of these deposits and the origin of the carbonic inclusions are still unclear. This study attempts to explain where the carbonic inclusions came from and their contribution to gold mineralization. The Sarekoubu gold deposit (SR) and the Qiaxia copper–gold deposit (QX) occur in the lower Devonian Kangbutiebao Formation (D1k22). Two types of quartz veins in these deposits can be distinguished: (1) lentoid or banded quartz veins (QI) parallel to the foliation of metamorphic rocks; and (2) chalcopyrite-bearing quartz veins (QII) cutting across the foliation of metamorphic rocks and banded sulfides.Three main types of fluid inclusions can be found in the quartz veins: CO2–H2O fluid inclusions (Type CW), carbonic inclusions (Type C), and salt-aqueous inclusions (Type W). The CO2-rich fluid inclusions (type CW and type C) occur both in the QI and QII veins. The fluid inclusion assemblage (FIA) method was applied in petrography study and thermometry data analysis. The results show that CO2-rich fluid inclusions have been trapped with the minimum temperatures ranging from 243 to 395°C for the early vein quartz stage (QI), and 230 to 328°C for late polysulfide quartz veins (QII) of the Sarekoubu deposit. For the Qiaxia deposit, the minimum trapping temperatures are from 201 to 382°C for QI, and from 207 to 365°C for QII respectively. The estimated minimum trapping pressures are from 110 to 330MPa which are in agreement with the P–T conditions of the regional metamorphism.The CO2-rich fluids in the vein gold mineralization at the Sarekoubu–Qiaxia area might be produced after peak regional metamorphism during the early Carboniferous to the Permian due to decomposition of marble and calcareous siltstone in the Lower Devonian Kangbutiebao Formation. High density carbonic inclusions in SR are much more abundant than in QX, indicating that regional tectonic stress in SR might be higher than in QX. The hydrothermal alterations are also much more intensive in SR than in QX, which may illustrate loss of water in CO2–H2O fluids in SR during the process of wall rock alterations and leaving CO2-rich fluids behind. The CO2-rich fluids may have played an important role in gold mineralization and modifying the VMS deposits.

How caldera collapse shapes the shallow emplacement and transfer of magma in active volcanoes

Calderas are topographic depressions formed by the collapse of a partly drained magma reservoir. At volcanic edifices with calderas, eruptive fissures can circumscribe the outer caldera rim, be oriented radially and/or align with the regional tectonic stress field. Constraining the mechanisms that govern this spatial arrangement is fundamental to understand the dynamics of shallow magma storage and transport and evaluate volcanic hazard. Here we show with numerical models that the previously unappreciated unloading effect of caldera formation may contribute significantly to the stress budget of a volcano. We first test this hypothesis against the ideal case of Fernandina, Galápagos, where previous models only partly explained the peculiar pattern of circumferential and radial eruptive fissures and the geometry of the intrusions determined by inverting the deformation data. We show that by taking into account the decompression due to the caldera formation, the modeled edifice stress field is consistent with all the observations. We then develop a general model for the stress state at volcanic edifices with calderas based on the competition of caldera decompression, magma buoyancy forces and tectonic stresses. These factors control: 1) the shallow accumulation of magma in stacked sills, consistently with observations; 2) the conditions for the development of circumferential and/or radial eruptive fissures, as observed on active volcanoes. This top-down control exerted by changes in the distribution of mass at the surface allows better understanding of how shallow magma is transferred at active calderas, contributing to forecasting the location and type of opening fissures.

Seismic activity and stress tensor inversion at Las Tres Vírgenes Volcanic and Geothermal Field (México)

We analyze local earthquakes occurring between 2003 and 2012 at the Las Tres Vírgenes Volcanic and Geothermal Field (TVVGF) to establish their temporal and spatial distribution, and relationships with local and regional fault systems, water injection, acid stimulation and steam production tests. We obtained focal mechanisms and inverted data for the stress tensor to understand the local and regional stress fields. We analyzed 423 local earthquakes with magnitudes between 0.1 and 2.9Mc and hypocentral depths from 0.2 to 7.4km b.s.l. The cutoff depth at ~7.4km possibly delineates the brittle–ductile transition zone. We identified seven swarms (from 1 to 7). Swarms 1 (December 2009), 2 (May 2010), 3 (June–July 2010) and 7 (December 2012) are strongly correlated with injection processes; whereas swarms 5 (April 2012) and 6 (September 2012) are correlated with local tectonic faults. Stress inversion showed NW–SE, E–W and NE–SW extensional orientations (Shmin), in agreement with the local tectonic stress field; while NE–SW compressional orientations (SHmax) are correlated with the regional tectonic stress field.

In-situ stress measurements and regional stress field assessment in the Xinjiang candidate area for China's HLW disposal

Altogether 180 hydraulic fracturing (HF) in-situ stress measurements were conducted in a pre-selected area in the Xinjiang Uygur Autonomous Region, China, which is being considered as one of the candidate areas for China's high-level radioactive waste (HLW) repository. In-situ stress magnitudes and orientations in three sub-areas (i.e., Yamansu, Tianhu and Aqishan sub-areas) were obtained from 163 valid measurement points in eight sub-vertical boreholes at depths ranging from 17 to 647m, and the variation of the in-situ stress components with depth was analyzed. The measurement results show that the maximum horizontal stress is larger than the vertical stress within most of the measurement depth ranges, indicating that the regional stress field is dominated by tectonic horizontal stress rather than by the overburden stress (σv). Within the range of the tested depths, the stress field is characterized by σH>σv>σh, where σH and σh are the maximum and minimum horizontal stresses, respectively. Fracture impression results reveal that the maximum horizontal stress is dominantly oriented in the NEE–SWW direction, which is in general in agreement with the orientation of regional tectonic stress field generated from movement of the Earth's tectonic plates and is consistent with those interpreted by GPS measurements and focal mechanism solutions. In addition, an abnormal phenomenon in performing stress measurements in one borehole was noticed and the result was discussed using borehole injection test data.

The bending mechanism of Anping ground fissure in the Hebei Plain, North China

The Anping fissure is one typical and particular ground fissure in the North China Plain. This study was carried out in Anping area with geological means, such as surveying, mapping, trenching and drilling. The geological structure and disasters were analyzed by both qualitative and quantitative methods. The main conclusions are as follows: (1) Anping ground fissure is the local manifestation of regional tectonic stress field and is basically folding directional, hidden and intermittent. (2) Under the control of Shen-rao fault, Anping ground fissure was exposed and expanded by water-related human activities, and then was cracked by small- and medium-sized earthquakes. (3) The forming process followed the bending-cracking rules. The uplifting force from deep in the earth bent the entire overlying strata. The tangential stress below the ground surface counterbalanced the horizontal stress of soils, even breaking through their tensile strength and inducing cracks. The fissure was periodic and wavery, because the cracking force was proportional to the uplifting force but inversely proportional to the stratigraphic depth.

Analysis of Foreshock Sequences in California and Implications for Earthquake Triggering

We analyze foreshock activity in California and compare observations with simulated catalogs based on a branching aftershock-triggering model. We first examine foreshock occurrence patterns for isolated \(M \ge 5\) earthquakes in southern California from 1981 to 2011 and in northern California from 1984 to 2009. Among the 64 \(M \ge 5\) mainshocks, excluding 3 swarms and 3 doubles, 53 % of the rest are preceded by at least one foreshock within 30 days and 5 km. Foreshock occurrence appears correlated with mainshock faulting type and depth. Foreshock area is correlated with the magnitude of the largest foreshock and the number of foreshocks, however, it is not correlated with mainshock magnitude. We then examine the occurrence pattern of all seismicity clusters without a minimum magnitude requirement, and the possibility that they are “foreshocks” of larger mainshocks. Only about 30 % of the small clusters lead to a larger cluster. About 66 % of the larger clusters have foreshock activities, and the spatial distribution pattern is similar to \(M \ge 5\) mainshocks, with lower occurrence rates in the Transverse Range and central California and higher occurrence rates in the Eastern California Shear Zone and the Bay Area. These results suggest that foreshock occurrence is largely controlled by the regional tectonic stress field and fault zone properties. In special cases, foreshock occurrence may be useful for short-term forecasting; however, foreshock properties are not reliably predictive of the magnitude of the eventual “mainshock”. Comparison with simulated catalogs suggest that the “swarmy” features and foreshock occurrence rate in the observed catalogs are not well reproduced from common statistical models of earthquake triggering.

Tectonic rotations and internal structure of Eocene plutons in Chuquicamata, northern Chile

A paleomagnetic and AMS study on Eocene plutonic complexes in the Calama area, northern Chile, reveals high-temperature, high-coercivity magnetizations of dominantly thermoremanent origin and magnetic fabrics controlled by magnetite. The paleomagnetic results indicate that ~43Ma plutons underwent clockwise tectonic rotation, whereas adjacent ~39Ma plutons did not undergo discernible rotation. This points to a middle Eocene age for the younger tectonic rotations associated with the Central Andean Rotation Pattern in the Chuquicamata–Calama area.The petrofabric in these rocks formed under conditions ranging from purely magmatic (i.e. before full crystallization) to low-temperature solid-state deformation. AMS and paleomagnetism suggest that the plutonic bodies were formed by progressive amalgamation of subvertical magma sheets spanning multiple magnetic polarity chrons. The parallelism between magmatic and tectonic foliations suggests that regional tectonic stress controlled ascent, emplacement and rock deformation during cooling. In this context, we suggest that magma ascent and emplacement in the upper crust likely exploited Mesozoic structures which were locally reactivated in the Eocene.

Holocene displacement field at an emerged oceanic transform-ridge junction: The Husavik-Flatey Fault – Gudfinnugja Fault system, North Iceland

Our research focuses on Holocene tectonics in a broad area surrounding the junction between the active NW–SE trending Husavik-Flatey transform fault (HFF) and the N–S Gudfinnugja normal fault (GF), an exceptional example of onshore transform-ridge intersection. We mapped 637 minor and major faults, and measured the dip-slip and strike-slip offset components on the major faults. We also mapped 1016 individual tension fractures, as well as opening directions on the most reliable ones. The results indicate that this portion of the HFF comprises major right-stepping segments, with both normal and right-lateral strike-slip components, linked by local normal faults. The entire GF always shows pure dip-slip normal displacements, with a strong decrease in offset at the junction with the HFF. Fissure opening directions are in the range N45°-65°E along the HFF, N90°E along the GF, and N110°E within the area south of the HFF and west of the GF. Fault kinematics and fissure openings suggest a displacement field in good agreement with most of present-day GPS measurements, although our data indicate the possible long-term Holocene effects of the superimposition of magma-related stresses on the regional tectonic stresses. The HFF and the GF work together as a structural system able to accommodate differential crustal block motion, and possibly past dyke intrusions.

Fault Movement Potentials in the Tehran-Semnan Region (North Iran)

The major Quaternary faults in the Tehran-Semnan region can be classified based on their strikes into three sets: northeast-southwest, northwest-southeast and east-west. In this paper, we use a model to evaluate fault movement potential (FMP). Their theoretical model is based on the relationship between fault geometrical characteristics and regional tectonic stress field. The results show that The Mosha, Emam Zadeh Davood and Pourlcan-Vardij fault zones have high FMP (0.9 or 90%) and the Parchin fault zone has very low FMP (0.0 - 0.1) in the area.