Left-lateral Strike-slip System Research Articles

Deep fluids migration and submarine emersion of the Kalang Anyar mud volcano (Java, Indonesia): A multidisciplinary study

North-east Java is part of a large sedimentary basin containing hydrocarbon provinces that feature diffuse hydrothermal systems, mud volcanoes, and degassing sites. Seismic profiles acquired to explore the basin reveal a broad distribution of palaeo- and modern piercement structures. The Watukosek fault system links the volcanic arc, to the south, with the Sidoarjo province, to the north. Several piercement structures, including the Kalang Anyar mud volcano, are hosted along this left-lateral strike-slip system that favors the migration of crustal fluids in this part of the basin. Here, we present a multidisciplinary geological, geophysical and geochemical study conducted at Kalang Anyar where dozens of seepage sites are active in the crater area and intermittently emit bursts oil, gas, mud, and water. The emitted gasses are methane-dominated with smaller amounts of heavier hydrocarbons and CO2. Unlike most mud volcanoes, at Kalang Anyar the mixed-thermogenic origin of the methane is coupled with geothermal anomalies, as indicated by helium and CO2 isotopic values (δ13CCO2 as high as −4‰) that suggest the input of mantle-derived gas. Our gas flux measurements reveal that Kalang Anyar emits about 1.62 and 5.75 t yr−1 of CO2 and CH4, respectively. The intense bubbling gives rise to a typical drumbeat seismic signal characterized by dominant frequencies around of 3–4 Hz (and up to 15 Hz). We interpret the drumbeat as fluids rising and resonating through shallow plumbing system of Kalang Anyar. Erupted clasts with different lithologies and shells are scattered across the mud volcano area, while the edges of the crater zone include cubic meter-sized carbonate-cemented blocks and ridges that contain siliciclastic sediments and abundant chemosymbiotic bivalves. Carbon isotope analyses of the carbonate cement (δ13C as low as −48.8‰) identify the latter as methanogenic chemoherms. Radiocarbon (14C) dating of bivalves cemented in the blocks indicates an age of 1890-1488 BP. These results indicate that the activity of Kalang Anyar MV dates from when the area was below sea level and that the microbially-mediated precipitation of carbonates was ongoing during subaqueous methane seepage at the crater site.To the best of our knowledge, Kalang Anyar is the first example of a mud volcano that progressed from subaqueous to subaerial conditions during marine regression, displaying evidence of former marine activity (i.e. methanogenic carbonates) and current subaerial degassing at numerous seepage sites. Potentially eruptive phases represent a clear geohazard for the numerous settlements constructed inside the mud volcano. In light of this, it may be prudent to apply stricter rules for development activities, such as housing construction permits that consider the possibility of potentially catastrophic events, and apply steps to mitigate these hazards.

Controls on fracture network characteristics of the middle member of the Bakken Formation, Elm Coulee field, Williston Basin, United States

Although most of the production from the Bakken Formation in the Elm Coulee field of the Williston Basin is interpreted to come from matrix permeability, plots of reservoir performance indicators, such as estimated ultimate recovery (EUR), show areas of anomalously high production believed to be caused by secondary (fracture) permeability. Recent studies have alluded to basement tectonics controlling the structure of the overlying sedimentary cover and thus the reservoir performance in the Elm Coulee field, but the exact controlling mechanism has not been demonstrated. This paper describes an antiformal structure overlying a zone of deformation in a seismic data set. The zone of deformation consists of small vertical offset faults displaying evidence of wrench faulting and involves the Bakken petroleum system and deeper units. An analog model is used to guide interpolation and extrapolation of the faults when they are traced through the data cube. With the help of analog models, it is established that the antiformal structure and the associated deformation zone evolved over a stepover in a northwest-southeast–oriented left-lateral–strike-slip system in the rigid basement. This strike-slip system may be secondary to the regional left-lateral Brockton-Froid fault zone, which lies to the north of the study area. The fracture network in the Elm Coulee field is likely to be enhanced around such antiformal structures, providing a plausible explanation for the locations of the EUR sweet spots. Thus, it is proposed that locating such deformation zones forms a potential new exploration trend in this field.

Seismostratigraphy and tectonic architecture of the Carboneras Fault offshore based on multiscale seismic imaging: Implications for the Neogene evolution of the NE Alboran Sea

In the SE Iberian Margin, which hosts the convergent boundary between the European and African Plates, Quaternary faulting activity is dominated by a large left-lateral strike–slip system referred to as the Eastern Betic Shear Zone. This active fault system runs along more than 450km and it is characterised by low to moderate magnitude shallow earthquakes, although large historical events have also occurred. The Carboneras Fault is the longest structure of the Eastern Betic Shear Zone, and its southern termination extends further into the Alboran Sea. Previously acquired high-resolution data (i.e. swath-bathymetry, TOBI sidescan sonar and sub-bottom profiler) show that the offshore Carboneras Fault is a NE–SW-trending upwarped zone of deformation with a length of 90km long and a width of 0.5 to 2km, which shows geomorphic features typically found in subaerial strike–slip faults, such as deflected drainage, pressure ridges and “en echelon” folds. However, the neotectonic, depth architecture, and Neogene evolution of Carboneras Fault offshore are still poorly known. In this work we present a multiscale seismic imaging of the Carboneras Fault (i.e. TOPAS, high-resolution multichannel-seismic reflection, and deep penetration multichannel-seismic reflection) carried out during three successive marine cruises, from 2006 to 2010. The new dataset allowed us to define a total of seven seismostratigraphic units (from Tortonian to Late Quaternary) above the basement, to characterise the tectonic architecture and structural segmentation of the Carboneras Fault, and to estimate its maximum seismic potential. We finally discuss the role of the basement in the present-day tectonic evolution of the Carboneras Fault, and explore the northern and southern terminations of the fault and how the strain is transferred to nearby structures.

Global Positioning System constraints on the active tectonics of NE Iran and the South Caspian region

We present a velocity field compiled from a network of 27 permanent and 20 campaign GPS stations across NE Iran. This new GPS velocity field helps to investigate how Arabia–Eurasia collision deformation is accommodated at the northern boundary of the deforming zone. The present-day northward motion decreases eastward from 11 mm/yr at Tehran (∼52°E) to 1.5 mm/yr at Mashhad (∼60°E). N–S shortening across the Kopeh Dagh, Binalud and Koh-e-Sorkh ranges sums to 4.5±0.5 mm/yr at longitude 59°E. The available GPS velocities allow us to describe the rigid-body rotation of the South Caspian about an Euler pole that is located further away than previously thought. We suggest that two new stations (MAVT and MAR2), which are sited far from the block boundaries, are most likely to indicate the full motion of the South Caspian basin. These stations suggest that NW motion is accommodated by right-lateral slip on the Ashkabad fault (at a rate of up to 7 mm/yr) and by up to 4–6 mm/yr of summed left-lateral slip across the Shahroud left-lateral strike-slip system. Our new GPS results are important for assessing seismic hazard in NE Iran, which contains numerous large population centers and possesses an abundant historical earthquake record. Our results suggest that the fault zones along the eastern Alborz and western Kopeh Dagh may accommodate slip at much faster rates than previously thought. Fully assessing the role of these faults, and the hazard that they represent, requires independent verification of their slip-rates through additional GPS measurements and geological fieldwork.

Discrete Plio-Pleistocene phases of tilting and counterclockwise rotation in the southeastern Aegean arc (Rhodos, Greece): early Pliocene formation of the south Aegean left-lateral strike-slip system

The island of Rhodos represents an uplifted block in the largely submerged southeastern Aegean forearc. It has a complex history of subsidence, uplift and counterclockwise rotation during the Plio-Pleistocene, in response to the interplay between large-scale geodynamic processes. In this paper, we present a new chronostratigraphic framework for the continental Pliocene Apolakkia basin of southwestern Rhodos. We combine these time constraints with recently published chronostratigraphic data from the marine Plio-Pleistocene basins of northeastern Rhodos to reconstruct rotational and vertical motions. Our palaeomagnetic results identify two rotation phases for Rhodos: c . 10° (9 ± 6°) counterclockwise (ccw) rotation between 3.8 and 3.6 Ma, and c . 17 ± 6° ccw rotation since 0.8 Ma. Between these phases, Rhodos tilted to the SE, drowning the southeastern coast to a depth of 500–600 m between 2.5 and 1.8 Ma, then to the NW, which resulted in the re-emergence of the drowned relief between 1.5 and 1.1 Ma. We relate the rotations of Rhodos to incipient formation of the south Aegean sinistral strike-slip system and the foundering of the Rhodos basin. The previously shown absence of Messinian evaporites in the deep-marine Rhodos basin in combination with the 3.8 Ma onset of ccw rotation of Rhodos constrains the onset of the formation of the south Aegean strike-slip system between 5.3 and 3.8 Ma. The formation of this strike-slip system is probably related to the interplay of oblique collision between the southeastern Aegean region and the northward moving African plate, the westward motion of Anatolia, gravitational spreading of the overthickened Aegean lithosphere and the recently postulated southwestward retreat of the African subducted slab along a subduction-transform edge-propagator fault.

Neogene-Quaternary strike-slip tectonics in the central Calabrian Arc (southern Italy)

A Middle Miocene-Middle Pleistocene regional NW-SE left-lateral strike-slip fault system profoundly conditioned the evolution of central Calabria, during the late tectonic phases which involved the Apulian block and the Calabrian Arc. This system dissected an Oligocene-Early Miocene orogenic belt, made of Alpine nappes overthrusted the Apennine Chain. In the present study, three major faults, arranged in a right-hand en echelon pattern, have been identified within the mentioned strike-slip system: the Falconara-Carpanzano Fault, the Amantea-Gimigliano Fault, and the Lamezia-Catanzaro Fault. A wide active transtensional area (N-S-trending Crati Graben), developed since Late Pliocene, is located at the SE termination of the Falconara-Carpanzano Fault. In the sectors of overlapping of the faults, the transpressional regime induced tectonic extrusions of the deep-seated units of the Chain, producing push-ups within the overlying complexes. In particular, push-ups are either made of Mesozoic carbonate rocks at Mt. Cocuzzo–Mt. Guono and Mt. S. Lucerna, or of ophiolite rocks at Mt. Reventino and Gimigliano. In these sectors, the primary geometric relationships among the units of the orogenic belt were locally altered. The en echelon arrangement of the above-mentioned NW-SE major strike-slip faults indicates the existence of a left-lateral crustal shear zone, striking on average N160. The age of the regional NW-SE left-lateral strike-slip system deserves thorough investigation. Besides evidence from historical and instrumental earthquakes, and from paleoseismological investigations, the kinematic data suggests that the “cause” of the transtensional sector (Crati Graben) could be found in the regional Falconara-Carpanzano Fault.

Seismological Data of the Gulf of Aqaba Region

The Arabian Plate extends from the Gulf of Aden and Arabian Sea to southeastern Turkey, and from the Red Sea to the Zagros Mountains in Iran. It is bounded by all major types of tectonic margins: divergent, convergent, and transform (Figure 1). The Gulf of Aqaba is a narrow gulf that extends to the northeast from the top of the Red Sea (Figure 2). A spreading ridge plate boundary runs through the middle of the Red Sea (Ambraseys et al. , 1994). Growth of the Red Sea causes the Arabian Plate to move to the northeast with respect to the African Plate (Hempton, 1987). At the top of the Red Sea, the plate boundary changes to a transform fault that lies in the Gulf of Aqaba and continues north into the Dead Sea rift valley (Girdler, 1990). Tectonically, the Gulf of Aqaba is dominated by a northsouth left-lateral strike-slip system that resulted in the creation of three rhomb-shaped grabens filled with a few kilometers of sediments (Garfunkel, 1981). Such grabens have also been recognized in the United States as important structural elements along the transform plate boundary of southern California (Crowell, 1974). Examination of the epicenters of previously recorded earthquakes within the Gulf of Aqaba region indicates that the majority of the earthquakes occurred in or near the grabens. Figure 1. Map showing the tectonic boundaries of the Arabian Plate. Region with topographic elevation over 1,500 meters in the Iranian plateau is shown in gray. The large black arrows represent major plate motion directions. This paper provides an investigation into the historical and recent seismicity of the Gulf of Aqaba region, utilizing the newly compiled Saudi Arabian Earthquake Database catalog, which is now freely available (Al-Amri, 2000). Limited historic data on the seismicity of the Arabian Peninsula are available …

Shear partitioning in the eastern Nankai Trough: evidence from submersible dives

Submersible dives over the wedge of the easternmost Nankai Trough demonstrate the existence of a left-lateral strike-slip system parallel to the subduction zone. This system develops as the trench, turning northward toward land, becomes highly oblique to the motion. Although shear partitioning is well known in other subduction zones, the process here has the peculiarity of continuing northward into land.

Pre-transvaal wrench tectonics along the northern margin of the witwatersrand basin, South Africa

The pre-Transvaal tectonic history of the northern margin of the Witwatersrand basin is re-evaluated in terms of wrench fault tectonics. Three major east-northeast trending left-lateral wrench fault systems are recognized: the Sugarbush, Rietfontein, and Kromdraai systems. They are characterized by pull-apart basins (e.g., Bezuidenhout Valley and Kromdraai grabens), narrow slivers of displaced stratigraphy (e.g., Langermanskop, Rietfontein block) and marginal, convex upward thrusts. Changes in fault orientation result in areas of compression passing laterally into areas of extension over short distances. Splays terminate individual fault systems. Regions of wrench fault overlap are characterized by fold domains (e.g., West Rand syncline, East Rand basin), with folds characteristically trending NW-SE. The left-lateral strike-slip system appears to be of craton-wide scale and probably extends at least as far as the Barberton greenstone belt. The wrench system appears to have come into existence during Witwatersrand times, but experienced its major movement during middle Ventersdorp times. The left-lateral strike-slip system is believed to be related to rifting along the Ventersdorp trough, and to right-lateral faulting along the southwestern margin of the Witwatersrand basin. These tectonics occurred prior to a post-Transvaal period of folding and thrusting related to the emplacement of the Vredefort dome. The latter is responsible for the penetrative regional cleavage and bedding sub-parallel faults throughout the area concerned. The structural model proposed here has implications for the existence of possible outliers of mineralized upper Witwatersrand stratigraphy.

The Caracas, Venezuela, earthquake of July 1967: A multiple‐source event

A general study of Caribbean plate tectonics is first focused on the determination of fault parameters and source processes of the Caracas (Venezuela) earthquake of July 29, 1967 (mb = 6.5, Ms = 6.7). Synthetic seismograms which closely reproduce the observed P, SH, and Love wave seismograms were generated using generalized ray and mode theories. The results indicate a complicated faulting process, consisting of at least three separated sources aligned along a Nl0°W trending ‘en echelon’ vertical left lateral strike slip system of three faults that ruptured from north to south, at three discrete places with an extreme separation of 90 km. The process of rupture progressed southward with a mean velocity of 3 km/s. The focal depths of the individual sources varied between 8 and 27.5 km. The total dislocation was calculated as 120 cm along the direction N 10°W, and the total average moment as 4 × 1026 dyn cm. The multiple character of the event severely constrains the number of suitable source models that can be inferred, thus facilitating the process of inversion. Tectonic implications are briefly discussed, and local geology is successfully invoked to support the source model.