Fault (geology)

About: Fault (geology) is a research topic. Over the lifetime, 26732 publications have been published within this topic receiving 744535 citations.

The continuity of active fault systems in Greece

Abstract: Summary Evidence from geomorphology, the distribution of large earthquakes, and geodetic measurements suggests that the active faulting in mainland Greece and the north Aegean Sea is concentrated into a small number of discrete, linear zones that bound relatively rigid blocks. On land, the zones are most clearly identified where the faulting is associated with large escarpments, particularly in hard footwall rocks. The zones can become indistinct and diffuse near their ends, sometimes because they enter high, unstable topography where landsliding obscures the fault morphology, but mostly because the extension rates decrease along strike as a consequence of the relative rotation of the blocks they bound. The main graben systems of Chalkidiki, southern Thessaly and the North Gulf of Evia all seem to connect with the strike-slip faulting in the offshore Aegean and to die out in the west, a configuration related to clockwise rotations in east-central Greece. By contrast, the Gulf of Corinth, which is the fastest opening graben system in Greece, opens more rapidly in the west than the east. Both these features of the Gulf of Corinth are consequences of the motion of the south Aegean and Peloponnese as a single block. Late Pliocene and Quaternary geology and geomorphology indicate that the boundaries of the rigid blocks in central Greece have changed over that time, with faulting migrating into the hanging walls, sometimes changing in orientation. These changes are probably related to the way faulting in the seismogenic layer adapts to block rotation, so as to maintain the general features of a velocity field that is controlled by larger scale effects, such as buoyancy forces and the seaward migration of the subducting slab beneath Crete. The image of Greece as a mosaic of rigid blocks whose boundaries change with time is a useful framework for seismic hazard evaluation, but we emphasize that some moderate-sized earthquakes do occur away from the main fault zones, within the relatively rigid blocks and especially near their diffuse ends.

The 17 August 1999 Izmit Earthquake

Abstract: On 17 August 1999, an earthquake of magnitude 7.4 shook northwestern Turkey. Details on the earthquake9s characteristics and effects across northwestern Turkey are provided and are put in the historical context of previous earthquakes in the region. The earthquake was the seventh in a series of earthquakes migrating westwards along the North Anatolian fault since 1939. Information on historical earthquakes, modeling and estimates of the slip rate along the fault indicate that the location and severity of the earthquake should not have come as a surprise.

Fault structure and mechanics of the Hayward Fault, California, from double-difference earthquake locations

Abstract: [1] The relationship between small-magnitude seismicity and large-scale crustal faulting along the Hayward Fault, California, is investigated using a double-difference (DD) earthquake location algorithm. We used the DD method to determine high-resolution hypocenter locations of the seismicity that occurred between 1967 and 1998. The DD technique incorporates catalog travel time data and relative P and S wave arrival time measurements from waveform cross correlation to solve for the hypocentral separation between events. The relocated seismicity reveals a narrow, near-vertical fault zone at most locations. This zone follows the Hayward Fault along its northern half and then diverges from it to the east near San Leandro, forming the Mission trend. The relocated seismicity is consistent with the idea that slip from the Calaveras Fault is transferred over the Mission trend onto the northern Hayward Fault. The Mission trend is not clearly associated with any mapped active fault as it continues to the south and joins the Calaveras Fault at Calaveras Reservoir. In some locations, discrete structures adjacent to the main trace are seen, features that were previously hidden in the uncertainty of the network locations. The fine structure of the seismicity suggests that the fault surface on the northern Hayward Fault is curved or that the events occur on several substructures. Near San Leandro, where the more westerly striking trend of the Mission seismicity intersects with the surface trace of the (aseismic) southern Hayward Fault, the seismicity remains diffuse after relocation, with strong variation in focal mechanisms between adjacent events indicating a highly fractured zone of deformation. The seismicity is highly organized in space, especially on the northern Hayward Fault, where it forms horizontal, slip-parallel streaks of hypocenters of only a few tens of meters width, bounded by areas almost absent of seismic activity. During the interval from 1984 to 1998, when digital waveforms are available, we find that fewer than 6.5% of the earthquakes can be classified as repeating earthquakes, events that rupture the same fault patch more than one time. These most commonly are located in the shallow creeping part of the fault, or within the streaks at greater depth. The slow repeat rate of 2–3 times within the 15-year observation period for events with magnitudes around M = 1.5 is indicative of a low slip rate or a high stress drop. The absence of microearthquakes over large, contiguous areas of the northern Hayward Fault plane in the depth interval from ∼5 to 10 km and the concentrations of seismicity at these depths suggest that the aseismic regions are either locked or retarded and are storing strain energy for release in future large-magnitude earthquakes.

Tectonic inheritance and continental rift architecture: Numerical and analogue models of the East African Rift system

Abstract: [1] The western branch of the East African Rift is composed of an arcuate succession of elongate asymmetric basins, which differ in terms of interaction geometry, fault architecture and kinematics, and patterns of uplift/subsidence and erosion/sedimentation. The basins are located within Proterozoic mobile belts at the edge of the strong Tanzanian craton; surface geology suggests that the geometry of these weak zones is an important parameter in controlling rift development and architecture, although other processes have been proposed. In this study, we use lithosphere-scale numerical models and crustal-scale analogue experiments to shed light on the relations between preexisting structures and rift architecture. Results illustrate that on a regional scale, rift localization within the mobile belts at the curved craton's western border results in an arcuate rift system, which implies that under a constant extensional stress field, part of the western branch experienced orthogonal extension and part oblique extension. Largest depocenters are predicted to form mostly orthogonal to the extension direction, and smaller depocenters will form along the oblique parts of the rift. The varying extension direction along the rift zone furthermore results in lengthwise varying rift asymmetry, segmentation characteristics, and border fault architecture (trend, length, and kinematics). Analogue models predict that discrete upper crustal fabrics may influence the location of accommodation zones and control the architecture of extension-related faults at a local scale. Models support that fabric reactivation is responsible for the oblique-slip kinematics on faults and for the development of Z-shaped or arcuate normal faults typically documented in nature.

Rupture process of the 2011 Tohoku‐oki earthquake and absolute elastic strain release

Abstract: [1] On 11 March 2011, the Tohoku-oki earthquake in eastern Japan and the devastating tsunami that followed it caused severe damage and numerous deaths. To clarify the rupture process of the earthquake, we inverted teleseismic P-wave data applying a novel formulation that takes into account the uncertainty of Green's function, which has been a major error source in waveform inversion. The estimated seismic moment is 5.7 × 1022 Nm (Mw = 9.1), associated with a fault rupture 440 km long and 180 km wide along the plate interface. The source process is characterized by asymmetric bilateral rupture propagation, but we also found continuous slips up-dip from the hypocenter, which led to a large maximum slip (50 m), long slip duration (90 s), and a large stress drop (20 MPa). The long slip duration, large stress drop, extensional (normal faulting) aftershocks in a previously compressional stress regime, and low-angle normal slips at approximately the depth of the plate interface suggest that the earthquake released roughly all of the accumulated elastic strain on the plate interface owing to exceptional weakening of the fault. The stress accumulated on the plate interface was about 20 MPa near the trench and 0–10 MPa in the down-dip source region.