Active Tectonic Structure Research Articles

Tectonic geomorphology and paleoseismology of the Angelochori fault segment of the Anthemountas extensional detachment fault, Central Macedonia, Greece: Paleoseismic evidence from the 1677 CE earthquake

This study presents the results of a geomorphological and paleoseismological investigation on the Angelochori normal fault. This fault controls the southern boundary of the Anthemountas basin and constitutes the western segment of the Anthemountas extensional detachment fault (AEDF), a ∼48 km-long, E-W-trending, north-dipping low-angle normal fault in Central Macedonia, Greece. To assess the relative tectonic activity of the Angelochori fault and to determine the number, timing, and displacement of surface-faulting earthquakes, we conducted detailed field mapping and paleoseismological investigations. Our approach involved utilizing geomorphic indices, analyzing stratigraphic and structural relations, considering luminescence ages, and employing OxCal modeling techniques. The acquired data reveal, for the first time, the Middle-Late Holocene activity of the Anghelochori fault, providing constraints on the age of three strong (M > 6) surface-rupturing earthquakes over the last ∼7.7 ka. The youngest of these events aligns with the historical earthquake of the Anthemountas basin in 1677 CE. The observed minimum displacement per event ranges from 0.48 m to 0.65 m, consistent with a fault length estimated at about 24–28 km, suggesting an earthquake magnitude on the order of 6.6. The cumulative slip rate over the recorded period averages 0.21 ± 0.02 mm/a, with an average open recurrence interval of 2.6 ± 0.2 ka. Nonetheless, the displacement pattern displays alternating intervals of rapid slip at 0.60 ± 0.16 mm/a and slower slip at 0.08 ± 0.01 mm/a. Classified as Class 1, the Angelochori fault signifies an active tectonic structure posing a significant seismic hazard for the Thessaloniki metropolitan area.

Thermal springs associated with the Melilla-Fès-Smaala-Oulmès fault (Morocco): The role of fluid geochemistry in identifying a major active geodynamic structure

The thermal springs form a hydrothermal system implanted on the active tectonic structure of the Melilla - Fès - Smaala - Oulmès fault (MFSO). This fault forms a multiple play tectonic corridor generally oriented NE-SW parallel to the Nekor fault. It crosses two structural domains, the Meseta, to the South, and the Rif, to the North, forming a highly complex deep shear zone. The thermal waters from these springs have chloride-sodium facies and sodium-calcium bicarbonate facies with emergence temperatures between 24.4 and 53.6 °C. Along this fault, the pH of these waters varies centrifugally, with acidic values in the South and North and neutral values in the intermediate sector. Important information about the origin of thermal waters and the characteristics of the reservoirs is provided by the chemical compositions (chemical elements, isotopes, and gases) of these waters involving rock-water-gas interaction during their circulation in depth and flow to the surface, through different types of reservoirs intersected by the fracture networks associated to the MFSO. These reservoirs correspond to the crystalline basement and its Triassic evaporitic clay, Jurassic carbonate, Cretaceous marl, and Miocene saliferous cover, whose temperatures have been estimated between 100 and 200 °C. The stable isotopic compositions (−8.39 to −5.2‰ for δ18O and −51.2 to 30.1‰ for δ2H) indicate a meteoric origin of these waters, whose recharge areas are located in the Rif and Atlas reliefs. The gas phase present in the waters shows δ13Cco2 (−19.3 ‰ to −4,25 ‰) and 3He/4He (0.203–3.864 Ra) with mantellic signature, implying that the fault is deeply rooted. The mantellic helium content decreases progressively in these waters from SE to NE, following the direction of the MFSO fault, from the emergencies in the Palaeozoic basement to the springs in the secondary and Tertiary formations of the Prerif and Mesorif. This decrease results probably from the mixing with gases derived from the thick secondary and Tertiary sedimentary cover. These waters would also collect these gases during their interactions with these sedimentary formations. Towards the NE, these waters, which rise within the formations of the Mediterranean arc, are also influenced by gases derived from the sediments of volcanic arcs.The MFSO fault, which is permeable due to its fracture network, favours the diffusion of heat and the upwelling of mantle gases, which are collected by the fluids that will interact with the rocks during their circulation at depth and flow to the surface. Its hydraulic character, highlighted in the North by seismic tomographic sections, confirms the presence of fluids at a depth of 5 km. This hydraulic character is continuous towards the South, implying the intimate association of the springs studied with this active tectonic structure. The pressure generated by these fluids and the precipitation of secondary clay minerals will weaken this fault, giving it an aseismic character.

Fault displacement analysis using a multidisciplinary approach on the Gerede Segment of the North Anatolian Fault Zone

The North Anatolian Fault Zone (NAFZ) is the world's most seismically significant strike-slip fault and Turkey's most active tectonic structure. A segment of NAFZ known as Gerede is located in northwest Turkey. It is debatable whether the Gerede segment of the NAFZ exhibits evidence of tectonic creep formation. The movement of the Gerede Segment of the NAFZ was investigated using various methods in this study. The Global Navigation Satellite System (GNSS) and soil mechanics-based methods were used in the Gerede Segment of the NAFZ for fault displacement analysis using a multidisciplinary approach. The GNSS technique is widely used in geodynamics-kinematics and cartography studies of earth crust movements, as well as in determining deformations during earthquake periods and as a source of data in defining geological and atmospheric phases. By establishing a GNSS network composed of regional or geodetic station points around the fault zone, it is possible to determine the deformations, velocities, and possible seismic slip rates of permanent GNSS stations on this network. The shear box test is used in soil mechanics to determine the shear strength parameters c and φ. A shear box test is performed to determine the pattern of fault movement (seismic or aseismic) and to determine the shear strength parameters (c, φ). An undisturbed block sample from a paleoseismology trench was used for a consolidated drained (CD) type shear box test. It was found that the fault movement near the Gerede Segment was not creeping. This study makes a new contribution to the debate on whether the Gerede Segment's movement pattern is creep or seismic.

Volcano-tectonic interactions at the southern margin of the Okataina Volcanic Centre, Taupō Volcanic Zone, New Zealand

The c. 15 km-long Ngapouri-Rotomahana Fault (NRF) is a major splay of the Paeroa Fault at the eastern margin of the modern Taupō Rift, the active tectonic structure embedded within the Taupō Volcanic Zone of North Island, New Zealand. The NRF and Paeroa Fault extend to the southern margin of the Okataina Volcanic Centre (OVC) and lie southwest of the Tarawera vent lineation, which is the source of approximately half of the eruptions of the OVC in the past 25 cal. ka BP. Here, we explore volcano-tectonic relationships between the OVC and the NRF and Paeroa Fault. Collective evidence used in our analysis includes: volcanic processes interpreted as occurring during the historic 1886 Tarawera (basalt) and the prehistoric 1314 ± 12 CE Kaharoa (basalt triggered rhyolite) eruptions, both on the Tarawera vent lineation; exposures in five trenches excavated across the NRF and seven trenches across the Paeroa Fault; data on a series of explosion craters formed to the southwest of the volcano associated with the ~1314 CE Kaharoa eruption and the Rotoma rhyolite (~9.4 cal. ka BP) eruption from the OVC; and mafic dykes that primed several of the OVC eruptions. Data from the twelve trenches on the two faults reveal eight surface fault ruptures since 15.6 cal. ka BP, with most closely coinciding with volcanic eruptions, providing a first-order indication of probable causality. Three principal modes of interaction are identified. Firstly, large displacement events on the Paeroa fault, arguably immediately prior to the Mamaku and Rotoma rhyolite eruptions (~7.9 and ~9.4. cal. ka BP, respectively) and on the NRF immediately prior to the ~1314 CE Kaharoa eruption are candidates for earthquake static or dynamic stress triggers for those explosive eruptive events. Secondly, basalt dyke intrusion was also involved in the initiation of the Kaharoa eruption, so the spatial and temporal relationships between dyke intrusion, smaller displacement fault ruptures and initiation of the Kaharoa eruption appear closely connected. Thirdly, faulting events that are interpreted as co- or post-eruption may be the result of stress triggers associated with magma chamber deflation.

Duvalo “Volcano” (North Macedonia): A Purely Tectonic‐Related CO2 Degassing System

AbstractDuvalo “volcano” is a site of anomalous geogenic degassing close to Ohrid (North Macedonia) not related to volcanic activity, despite its name. CO2 flux measurements made with the accumulation chamber (321 sites over ∼50,000 m2) showed fluxes up to nearly 60,000 g m−2 d−1, sustaining a total output of ∼67 t d−1. Soil gas samples were taken at 50 cm depth from sites with high CO2 fluxes and analyzed for their chemical and isotope composition. The gas is mainly composed by CO2 (>90%) with significant concentrations of H2S (up to 0.55%) and CH4 (up to 0.32%). The isotope compositions of He (R/RA 0.10) and of CO2 (δ13C ∼ 0‰) exclude significant mantle contribution, while δ13C‐CH4 (∼−35‰) and δ2H‐CH4 (∼−170‰) suggest a thermogenic origin for CH4. The area is characterized by intense seismic activity and Duvalo corresponds to an active tectonic structure bordering the Ohrid graben. The production of H2S within the stratigraphic sequence may be explained by thermochemical reduction of sulfate. The uprising H2S is partially oxidized to sulfuric acid that, reacting with carbonate rocks, releases CO2. The tectonic structure of the area favors fluid circulation, sustaining H2S production and oxidation, CO2 production and allowing the escape of the gases to the atmosphere. In the end, Duvalo represents a tectonic‐related CO2 degassing area whose gases originate mostly, if not exclusively, in the shallowest part of the crust (<10 km). This finding highlights that even systems with trivial mantle contribution may sustain intense CO2 degassing (>1,000 t km−2 d−1).

Assessing active and capable faulting as best practice for post-earthquake reconstruction activities: the Sant’Eutizio Abbey case study, in the epicentral area of the 2016 central Italy seismic sequence

Surface faulting is, together with strong ground shaking, a hazard associated with major earthquake faults. Assessing surface faulting potential of a given active tectonic structure is a fundamental prerequisite to adequately plan the use of territories and to perform new constructions, in order to act practices aimed to mitigate the associated risk. Assessing the surface faulting potential represents also ground for correctly performing re-construction and retrofitting of buildings and infrastructures during post-earthquake activities. We investigated a branch of a major seismogenic normal fault in the central Apennines of Italy, the Campi-Preci fault, along which the monumental Sant’Eutizio Abbey is located. The medieval Abbey is one of the most important cultural/religious edifices of the central Apennines, heavily damaged by the MW 6.5 October 30, 2016, earthquake, focused a few km to the south. Our study, based on field geological, geomorphological and structural survey and trenching investigations revealed that I) the trace of the Campi-Preci active fault branch is not actually located where presently reported in the available literature, II) the supposed morpho-tectonic features (basically, some km-long scarp carved on the Meso-Cenozoic carbonate bedrock), that suggested the presence of the fault segment in the area of the Sant’Eutizio Abbey, are not related to the active fault but are probably associated to a presently inactive reverse fault and III) the Sant’Eutizio Abbey is likely not potentially affected by primary surface faulting. Our work highlights that only a comprehensive multidisciplinary approach allows to correctly assess surface faulting potential in both seismotectonic and engineering perspectives.

Sentinel optical and SAR data highlights multi-segment faulting during the 2018 Palu-Sulawesi earthquake (Mw 7.5)

The main active tectonic structure in the western part of Central Sulawesi (Indonesia) is the left-lateral Palu-Koro strike-slip fault. Its offshore section was thought not to have broken during the Mw 7.5 Palu Earthquake on 28 September 2018, challenging the established knowledge of the tectonic setting at this location. Here, we use Sentinel-1 SAR interferometry to produce a map of the ground velocities in the area of the Mw 7.5 earthquake for the seven months following the 2018 earthquake. We show evidence of surface deformation along the western coast of the Palu bay, indicating that the Palu Koro offshore fault section might have contribute to or been affected by the earthquake. As the possibility of multi-segment ruptures is a high concern in the area because of the high seismic and tsunami hazard, we present here, a fault model that includes the offshore section of the Palu-Koro fault. Thanks to four independents space-based geodetics measurements of the co-seismic displacement (Sentinel-1 and Sentinel-2 correlograms) we constrain the 3D co-seismic ground displacements. The modeling of these displacements allows us to estimate the co-seismic fault slip amplitude and geometry at depth. At the end, we consider the multi-segment faulting scenario, including the offshore section of the Palu-Koro fault, as a plausible model to explain the submarine landslides and the tsunamis. This study also gives the opportunity to observe a super-shear earthquake in the context of a complex fault network and implies an increase in the probability of submarine landslides within the bay in the forthcoming years.

Soil gas radon concentrations along the Ganos Fault (GF)

In this study, soil radon levels have been measured for the first time across the Ganos fault (GF), which is known as the western part of the North Anatolian Fault Zone. LR 115 Type 2 Solid State Nuclear Track Detectors (time integrated) have been applied to determine soil gas radon levels, and the survey was performed in 16 stations along the fault line. The results showed that soil gas radon concentrations and variation of concentration levels are comparable high along the fault line. It is also observed that in the middle of the Ganos Fault, fairly elevated radon levels were detected. These can be related to the activity of the fault lines. It is confirmed that the study area has a very active tectonic structure and is great location for analyzing radon variations.

Geotechnical Handicap of Travertine with Different Lithotype Levels as Foundation Material

Abstract: Two major earthquakes occurred on October 23rd, 2011 (M=7.1) and November 9th, 2011 (M=5.6) in Tabanli and Edremit districts of Van province in Turkey, respectively. New settlement areas for Van city were determined after these destructive earthquakes. One of the most important areas for new settlements to be built was Edremit region, consisting travertine where nearly 80% of new housing units (12.384) were built by TOKI (Housing Development Administration of Turkey). Travertines have different lithotypes depending on their depositional process such as crystalline crust, shrub, reed which can affect mechanical and engineering properties of travertine and each level has different handicaps. The purpose of this study is to investigate the relationship between lithotype and physico-mechanical properties of travertines. According to the results, lithotype has an effect on physical, mechanical and rock mass properties of travertine. It is ascertained by several research methods that various handicaps may occur on such areas when the active tectonic structure of the area is evaluated along with the karstic cavities within the travertine and different lithotype qualities.

Tilt offset associated with local seismicity: the Mt. Etna January 9, 2001 seismic swarm.

AbstractOn the 9thof January 2001 a seismic swarm on the southeastern flank of Mt. Etna at 3.5 km beside sea level (b.s.l.), caused co-seismic variations on short and long baseline tiltmeters of the Mt. Etna permanent tilt network.Taking account of the geometry and mechanism of the active tectonic structure obtained by seismological studies, the theoretical tilt linked to the faulting source was calculated at multiple different recording stations. It was found that the amount of measured deformation exceeded that which was generated seismically, indicating that much of the deformation along the fault was aseismic.The 9 January 2001 episode represents a shear response to a local stress caused by a volcanic source that acted in the period preceding the 2001 eruption. Tilt data also suggest a marked slip of 70-140 cm along the fault, probably due to the presence of fluids.

Seismic slip on the west flank of the Upper Rhine Graben (France–Germany): evidence from tectonic morphology and cataclastic deformation bands

Abstract The Upper Rhine Graben (URG) is a seismically active tectonic structure in intraplate Europe. Large and moderate earthquakes have occurred along the URG in the past but no coseismic surface faulting has been reported so far. We investigated active faulting along the western edge of the northern URG and identified the 25 km-long linear Riedseltz–Landau normal fault scarp as a major tectonic structure affecting late Pleistocene and Holocene deposits. The fault zone is exposed in the Riedseltz quarry where it affects Pliocene sand and gravels and overlying late Pleistocene (Wurm) units. These units have not been buried deeper than a few tens of metres and yet the fault zone contains cataclastic deformation textures. Cataclasis is demonstrated by spalling and transgranular fractures in quartz grains concentrated in deformation bands with reduced grain size. The observed microstructures suggest multiple phases of deformation with cataclasis followed by emplacement of a prominent Fe-oxide matrix into deformation bands, and later emplacement of a clay-rick matrix into fractures. Previous geological and geophysical studies along the fault show late Pleistocene (Wurm) loess deposits ( c. 24–10 ka before present) and early Holocene sand–silty deposits with individual or cumulative 1.5 and 0.7 m surface slip, respectively. Field observations and previous results from shallow geophysics provide a minimum 0.15 mm a −1 time-averaged slip rate. The Riedseltz fault parameters integrated in a dislocation model suggest a minimum Mw 6.6 earthquake as a plausible scenario in the northern URG. The observations of cataclasis in shallowly buried sediments coupled with observations of the late Quaternary fault scarp call for palaeoseismic studies that may document the occurrence of a larger earthquake on the western edge of URG. Surface faulting of young, shallowly buried sediments associated with cataclasis provides new evidence for assessing the occurrence of large earthquakes and seismic hazard assessment in the northern URG.

A Model of Composite Seismic Sources for the Lower Rhine Graben, Northwest Europe

Abstract The Lower Rhine Graben (LRG) straddling the border zone of Belgium, the Netherlands, and Germany, is an active tectonic structure in continental northwest Europe. It is characterized by northwest–southeast oriented normal faults, and moderate but rather continuous seismic activity. Many faults have been mapped in the LRG, but so far a model of fault hierarchy or fault segmentation has been lacking. In the frame of a European database of seismogenic sources, we have devised a seismic‐source model for the LRG consisting of so‐called composite seismic sources. Each composite seismic source may encompass one or more segments, but it is unlikely that a segment would extend across more than one source. We distinguish 15 seismic sources based on major stepovers, bifurcations, gaps, and important changes in strike, dip direction, or slip rate. The sources are partitioned into one or more informal fault sections, each with an associated surface trace. For each source, we describe the limits and the composing fault sections, and present the geological arguments for their existence. We have compiled all relevant data concerning the seismic‐source parameters required for the database, putting lower and upper bounds on strike, dip, rake, slip rate, and depth, and an upper bound on earthquake magnitude. This source model should provide a new basis for modeling seismic hazard, as well as for guiding further paleoseismic studies in the LRG. Online Material: Detailed maps of the composite sources in the Lower Rhine Graben, 3D views of the fault model, and a table with parameters of earthquake focal mechanisms and detailed information sheets for each composite seismic source.

Large Holocene Earthquakes in the Lower Tagus Valley Fault Zone, Central Portugal

More than 100 years ago, a moderate-size earthquake affected several towns within the Lower Tagus Valley with major destruction in the town of Benavente and two other villages (Fonseca and Vilanova 2010). The earthquake, known as the 1909 Benavente earthquake, was studied rigorously by both contemporaneous (Chofat and Bensaude 1912) and modern scientists ( e.g. , Stich et al. 2005). Other historical earthquakes that caused major damage within the Lower Tagus Valley include the poorly constrained 1344 Mw 6.7 earthquake, the 1531 Mw 6.9 earthquake, the 1755 Mw 8.5 earthquake, and the 1858 Mw 7.1 earthquake (magnitudes according to Vilanova and Fonseca 2007). Instrumental seismicity in this area is generally sparse, with earthquakes too small to resolve focal mechanisms along a possible seismogenic structure (Figure 1). However, due to at least two historical earthquakes (including the 1909 Benavente earthquake) with isoseismals centered or within the Lower Tagus Valley, seismic activity in this region has been attributed to vaguely specified northeast-southwest trending tectonic structures usually referred to as the Lower Tagus Valley fault zone. Reviewed published maps ( e.g. , Servicos Geologicos e Portugal 1952, 1977, 1999; Cabral et al. 2004) do not show any active tectonic structure along the Lower Tagus Valley except for northwest-southeast trending faults that cut through Jurassic and Miocene lithologies in the vicinities of Vila Franca de Xira, Azambuja, and Santarem. The neotectonic map of Ribeiro and Cabral (1988) includes a long and rectilinear NNE-SSW fault along the Lower Tagus Valley with an unknown dip and a downthrown northwest block. The 1:500,000 geologic map includes an index map that shows the outline of the Quaternary active faults including a probable thrust fault transecting the Lower Tagus Valley (Servicos Geologicos de Portugal 1992). Previous work on the stress pattern in the Iberian region utilizing …

Magnetic characteristics of fracture zones and constraints on the subsurface structure of the Colima Volcanic Complex, western Mexico

Detailed magnetic anomaly surveys over the central and southern sector of the Colima rift, western Mexico, are used to investigate the subsurface structure and faults and/or fractures in the volcanic terrains formed by activity in the Colima volcanic complex (CVC). The CVC is located within the large north-south Colima rift in western Mexico. The Colima rift is a major active tectonic structure, trending perpendicular to the Middle America Trench and related to subduction of the Rivera and Cocos plates. Volcanic activity in the CVC has migrated southward toward the trench. Analyses of faults and recent deformation in the CVC and Colima rift are of major interest in volcano-tectonic studies and for hazard assessment. Structural analyses and fault mapping, however, are difficult because young volcanic and pyroclastic rocks obscure structural features and stratigraphy. Most of the southern Colima rift is covered by volcanic avalanches and volcaniclastic units, which have resulted in resurfacing of the volcanic terrains. Here we show that magnetic anomalies permit identification of faults and mapping of volcano-sedimentary and volcanic units. Total magnetic field measurements spaced every 0.5 km along 8 profiles, with an overall length of 284.5 km and covering the CVC sector of the Colima rift, have been obtained. We recognize fractures and fault zones of local and regional character from their characteristic magnetic anomaly response. Large mapped structures include the north-south Montitlan, northeast-southwest La Lumbre, and east-west La Escondida faults, which can be traced across the area from the magnetic profiles. Fault magnetic anomalies are modeled by lateral contrasts in terms of step models assuming thin dipping elongated zones along the fault planes. The study shows that faults in the CVC volcanic terrain can be investigated by magnetic surveying.

Scientists investigate recent Philippine landslide

A massive landslide devastated the community of Barangay Guinsaugon, Municipality of St. Bernard, Southern Leyte Province, Philippines, at about 10:30 local time on 17 February The landslide occurred along the steep fault scarp of the Philippine Fault Zone (PFZ) (Figure 1a), a large and active tectonic structure that traverses the entire length of the Philippines [Allen, 1962]. Barangay Guinsaugon is located at the foot of the scarp, directly in the path of the downward moving mass of earth. As of 24 February the landslide caused 122 confirmed deaths; 1,328 people still are missing.

3-D velocity structure in the central-eastern part of Qilianshan

The 3-D velocity tomography image of the central-eastern part of Qilianshan is obtained by the joint inversion of 3-D velocity structure and focal parameters based on the S-P data of micro-earthquakes recorded by the digital seismic network set up for a Sino-French cooperation program since 1996. The inversed velocity structure does primarily reflect some important features of the deep structure in the region and provide the scientific background for the further study of active tectonic structure and the calculation of earthquake parameters.

NEOTECTONIC DEFORMATION OF NORTH PARNIS

The morphotectonic analysis in the eastern part of Biotic Asopos river catchment, results to an explicit picture of a new drainage network with individual abnormalities that are focused mainly in phenomena of "piracy" and abrupt knick points. Topographic sections along the main streams and correlation between rose diagrams of faults and stream network reveal an influence of the drainage network (E-W and N-S direction) from the active tectonic structure of E-W to WNW-ESE direction, which is accompanied by phenomena of intense depth erosion transversely to the main active tectonic faults. The important dextral slip component of the main active fault zones (Sfendali-Avlona and Milesi Oropos) has influenced the alpine tectonic structure, determining the current NE-SW spread of Upper Cretaceous limestones and changing the direction of flysch axes from NNE-SSW in mountainous Parnis area to ENE-WSW in the flat area of Malakasa. The distribution of planation surfaces in combination with the presence of en echelon oblique slip faults of WNW-ESE direction, reveal a complex kinematic evolution, with main characteristics the progressive rotation of tectonic blocks to the WNW for the mountainous south area and to the SSW for the NE area of low relief.

Deep tectonic structure of Northwestern Attica, Greece: Geodynamic pattern of Athens earthquake

The study of Athens 09.07.1999 earthquake (Ms =5.9), which occurred in the area of the NW Attica peninsula within the Thriasio neotectonic basin, shed light to the complicated active tectonic structure of Attica. The geological, gravity and magnetic data, as well as the results of InSAR analysis were jointly considered for a better understanding of the block tectonics and kinematics of the meisoseismal area, as well as block geodynamic related to the seismic event. The deep tectonic structure is characterized by existence of small (up to 20km) dimensions uplifted and subsided blocks of Paleozoic basement that defined the characteristic tectonic pattern of the area. The largest values of co-seismic subsidence, derived from InSAR analysis, are observed within the subsided blocks of epicentral area. This evidence, together with the results of field microtectonic observations, implies that this ensemble of blocks, during the seismic event, moved in accordance with block kinematics and under the approximately N-S tension, which is characteristic for Attica on its neotectonic history ranging from Mid Pleistocene to date

An experimental study of soil memory and preconsolidation adjacent to an active tectonic structure: the Meers fault, Oklahoma, USA

Special consolidation tests were run on undisturbed samples to study the ability of Quaternary soils adjacent to the Meers fault in southwestern Oklahoma to record and remember the maximum effective (preconsolidation) stresses they experienced during the faulting process. The results show that the soils record >60% of the applied total stresses as preconsolidation stresses in 2 s of loading time, indicating that these stresses could have been recorded during an earthquake faulting event. To record all of the applied total stresses as preconsolidation stresses (100% recording or memory), the loading needs to last at least 4–5 min.

Active Tectonic Structure and Seismic Ruins in Northwest China

Active Tectonic Structure and Seismic Ruins in Northwest China