The South Aegean active volcanic arc: relationships between magmatism and tectonics

Application of machine-learning algorithms for tephrochronology: a case study of Plio-Quaternary volcanic fields in the South Aegean Active Volcanic Arc

Active tectonics of the Ganzi–Yushu fault in the southeastern Tibetan Plateau

The Erongo complex is the largest of the Cretaceous igneous complexes in the Damaraland, Southern Etendeka Province, Namibia. Erongo is made up of a series of mainly silicic volcanic and intrusive units, like many of the Damaraland complexes, but it is unique by virtue of its size and well-preserved igneous sequence silicic magmas as well as tholeiitic and alkaline basalts.The goals of this study were to determine the ages and petrogenetic relationships of the silicic and basic units in the Erongo complex, and to contribute to understanding the magmatic evolution of the Damaraland province. As part of this investigation, Os isotope compositions were determined on basic rocks from the complex, and this is the first study of Os isotopes in the Etendeka Province. The Erongo is built up on a sequence of tholeiitic basaltic lavas which are compositionally equivalent to the Southern Etendeka flood basalts (Tafelberg type) and probably represent erosional remnants of these (see below). The felsic volcanic units at Erongo include two types of rhyodacites and one rhyolite. The most voluminous of these is the Ombu rhyodacite, which has a thickness of up to 500 m and makes up most of the topographic expression of the complex. The Ombu rhyodacite rests directly on the basal tholeiites in the southern and eastern part of the complex, but to the north and west, a second rhyodacite occurs below it, the Erongorus rhyodacite ...

Cenozoic tectonic lineaments of the Terra Nova Bay region, Ross Embayment, Antarctica

Control of strike-slip faulting on reservoir formation of oil and gas in Nanpu sag

Age distribution of lamproites along the Socovos Fault (southern Spain) and lithospheric scale tearing

Stress transfer from the great 1964 Prince William Sound earthquake is modeled on the Denali fault, including the Denali-Totschunda fault segments that ruptured in 2002, and on other regional fault systems where M 7.5 and larger earth- quakes have occurred since 1900. The results indicate that analysis of Coulomb stress transfer from the dominant earthquake in a region is a potentially powerful tool in assessing time-varying earthquake hazard. Modeled Coulomb stress increases on the northern Denali and Totschunda faults from the great 1964 earthquake coincide with zones that ruptured in the 2002 Denali fault earthquake, although stress on the Susitna Glacier thrust plane, where the 2002 event initiated, was decreased. A southeasterly- trending Coulomb stress transect along the right-lateral Totschunda-Fairweather- Queen Charlotte trend shows stress transfer from the 1964 event advancing slip on the Totschunda, Fairweather, and Queen Charlotte segments, including the southern Fairweather segment that ruptured in 1972. Stress transfer retarding right-lateral strike slip was observed from the southern part of the Totschunda fault to the northern end of the Fairweather fault (1958 rupture). This region encompasses a gap with shallow thrust faulting but with little evidence of strike-slip faulting connecting the segments to the northwest and southeast. Stress transfer toward failure was computed on the north-south trending right-lateral strike-slip faults in the Gulf of Alaska that ruptured in 1987 and 1988, with inhibitory stress changes at the northern end of the northernmost (1987) rupture. The northern Denali and Totschunda faults, including the zones that ruptured in the 2002 earthquakes, follow very closely (within 3%), for about 90, an arc of a circle of radius 375 km. The center of this circle is within a few kilometers of the intersection at depth of the Patton Bay fault with the Alaskan megathrust. This inferred asperity edge may be the pole of counterclockwise rotation of the block south of the Denali fault. These observations suggest that the asperity and its recurrent rupture in great earthquakes as in 1964 may have influenced the tectonics of the region during the later stages of evolution of the Denali strike-slip fault system.

A study of the relative excitation of long-period surface waves from earthquake swarms near the Delfin basin in the northern Gulf of California and near the Queen Charlotte Islands fault suggests that a prominent mechanism of faulting for these swarm-type events was strike slip. Both swarms were apparently located on fracture zones near active spreading centers. Earlier studies have suggested that normal faulting may dominate oceanic earthquake swarms and that this type of faulting may be related to the occurrence of swarms. However, the present observations imply that the mechanisms for generating swarm-type earthquakes are probably due to factors other than the nature of the faulting involved. The suggested faulting mechanisms were determined by an examination of the relative amplitudes of Love and Rayleigh waves with periods between 10 and 50 s for some 60 events, assumed to be shallow (h < 15 km), that occurred in the northern Gulf of California. These surface waves were recorded at a new very long period seismograph station at Albuquerque, New Mexico. Bathymetry and seismicity of the northern Gulf of California suggest that faulting is occurring at short spreading centers (dip-slip faulting) and along transform faults (strike-slip faulting). Theoretical radiation patterns and relative amplitudes of Love and Rayleigh waves determined for both of these fault mechanisms were compared with the observed surface wave amplitudes recorded at Albuquerque. This technique provides a means of discriminating between the two possible types of focal mechanisms. The observations suggest that strike slip, possibly with a small component of dip slip, was the dominant faulting mechanism for many of these swarm-type events. Further support for this suggestion is provided by the observation of S-P times at a local (Δ < 100 km) short-period seismograph station, and thus the epicentral locations of these events are restricted to a portion of a mapped transform fault. This surface wave technique was also applied to an earthquake swarm that occurred near the Queen Charlotte Islands fault, and a similar conclusion was drawn.

The source parameters of all the moderate and strong events that occurred in the broader area of Zakynthos Island for the period 1997–2009 are determined using two different techniques depending on epicentral distance. For the strong events we employed teleseismic body-wave modeling between 30° and 90°, while for moderate events a regional moment tensor inversion approach was used. In both cases we used broadband waveform data with a good signal-to-noise ratio. The calculated focal mechanisms are representative of the displacement and strain fields of the broader area. Those associated with the Cephalonia transform fault are consistent with dextral strike-slip motion. The area between the island of Zakynthos and the Western coast of Peloponnese is also characterized by strike–slip faulting, while reverse faulting is mainly observed south of Zakynthos Island. Using both techniques, we also retrieved the source parameters of the biggest events of the seismic sequence of April 2006 near the southern coast of Zakynthos Island. The depths of the located events of the sequence vary mainly between 10 and 25 km. The fault plane solutions revealed thrust type faulting in all cases, something which can be related with upward motions in the southern part of the Island observed by DGPS measurements.

Origin of the shallow slip deficit on a strike slip fault: Influence of elastic structure, topography, data coverage, and noise

A recent Mw 4.3 earthquake proving activity of a shallow strike-slip fault in the northern part of the Western Desert, Egypt

The ENE striking Longmu Co fault and the North Altyn Tagh left-lateral slip fault have led to the complex regional structure in the northwestern Tibetan Plateau, resulting in a series of normal faulting and strike slip faulting earthquakes. Using both the ascending and descending Sentinel-1A/B radar images, we depict the coseismic deformation caused by the 2020 Yutian Mw 6.4 earthquake with a peak subsidence of ~ 20 cm. We determine the seismogenic fault geometry by applying the Bayesian approach with a Markov Chain Monte Carlo sampling method, which can better characterize the posterior probability density functions of the source model parameters. The estimation results reveal that the earthquake is a normal faulting event with a moderate strike slip component. Based on the optimal fault geometry model, we extend the fault plane and invert for the distributed coseismic slip model. The optimal slip model shows that the coseismic slip is mainly concentrated at shallow depths of 3–10 km with a maximum slip of ~ 1.0 m. Our preferred geodetic coseismic model exhibits no surface rupture, which may likely be due to the shallow slip deficit in the uppermost crust. We calculate the combined loading effect of the Coulomb failure stress changes induced by the coseismic dislocations and postseismic viscoelastic relaxation of the 2008 Mw 7.1, 2012 Mw 6.4 and 2014 Mw 6.9 Yutian events. Our study demonstrates that the three preceding major Yutian shocks were insufficient to trigger the 2020 Yutian earthquake, which we consider perhaps reflects the natural release of elastic strain accumulated mainly through localized tectonic movement. We attribute the 2020 Yutian event to the release of extensional stress in a stepover zone controlled by the Longmu Co and the North Altyn Tagh sinistral strike slip fault systems. The seismic risk in the southwest end of the North Altyn Tagh fault has been elevated by the Yutian earthquake sequences, which require future attention.

Long wavelength satellite gravity and geoid anomalies over Himalaya, and Tibet: Lithospheric structures and seismotectonics of deep focus earthquakes of Hindu Kush – Pamir and Burmese arc

The Lembang fault considering vulnerable because of the site is near downtown Bandung. The west Lembang segment is the rural area of Cibodas. The two opinions is emerging, become normal fault or strike slip fault, based on recent earthquake (2010 onward). The geology data show the structure is observed by the outstanding topographic extended about 20 km, with volcanic rock very dominant. The seismology data is analysed for year 2011 in Mw less than 3, and classical fault plane solution is obtained. The gravity data is better acquired than 0.1 mGal, with elevation precision better than 60 cm. The upward Continuation, and second vertical derivative, is applied on data, as well as modelling 2.5D. The section is presenting in one section only, while data is getting in larger area. The seismology data show mostly for event is strike slip although in several parts having event normal. The gravity data is not ideal as graben like structure but rather locally low about 10 mGal amplitude. The combining the two methods suggested the slip zone or sag pond is more possible for the local anomaly. Besides, the Lembang fault is extended toward north rather to west or south.

Fractures within granodiorite of the central Sierra Nevada, California, were studied to elucidate the mechanics of faulting in crystalline rocks, with emphasis on the nucleation of new fault surfaces and their subsequent propagation and growth. Within the study area the fractures form a single, subparallel array which strikes N50°–70°E and dips steeply to the south. Some of these fractures are identified as joints because displacements across the fracture surfaces exhibit dilation but no slip. The joints are filled with undeformed minerals, including epidote and chlorite. Other fractures are identified as small faults because they display left‐lateral strike slip separations of up to 2 m. Slickensides, developed on fault surfaces, plunge 0°–20° to the east. The faults occur parallel to, and in the same outcrop with, the joints. The faults are filled with epidote, chlorite, and quartz, which exhibit textural evidence of shear deformation. These observations indicate that the strike slip faults nucleated on earlier formed, mineral‐filled joints. Secondary, dilational fractures propagated from near the ends of some small faults contemporaneously with the left‐lateral slip on the faults. These fractures trend 25°±10° from the fault planes, parallel to the direction of inferred local maximum compressive stress. The faults did not propagate into intact rock in their own planes as shear fractures. Rather, adjacent faults were linked together by secondary, dilational fractures. Extensive secondary fracturing between faults produced larger fault zones that accommodate 10–100 m of left‐lateral slip. As deformation progressed, faulting evolved from relatively short, closely spaced faults to longer, more widely spaced fault zones.