Surface Rupture Length Research Articles

Surface slip distributions and geometric complexity of intraplate reverse-faulting earthquakes

Abstract Earthquake ground surface ruptures provide insights into faulting mechanics and inform seismic hazard analyses. We analyze surface ruptures for 11 historical (1968–2018) moment magnitude (Mw) 4.7–6.6 reverse earthquakes in Australia using statistical techniques and compare their characteristics with magnetic, gravity, and stress trajectory data sets. Of the total combined (summative) length of all surface ruptures (∼148 km), 133 km (90%) to 145 km (98%) align with the geophysical structure in the host basement rocks. Surface rupture length (SRL), maximum displacement (MD), and probability of surface rupture at a specified Mw are high compared with equivalent Mw earthquakes globally. This is attributed to (1) a steep cratonic crustal strength gradient at shallow depths, promoting shallow hypocenters (∼1–6 km) and limiting downdip rupture widths (∼1–8.5 km), and (2) favorably aligned crustal anisotropies (e.g., bedrock foliations, faults, fault intersections) that enhanced lateral rupture propagation and/or surface displacements. Combined (modeled and observed) MDs are in the middle third of the SRL with 68% probability and either the ≤33rd or ≥66th percentiles of SRL with 16% probability. MD occurs proximate to or directly within zones of enhanced fault geometric complexity (as evidenced from surface ruptures) in 8 of 11 earthquakes (73%). MD is approximated by 3.3 ± 1.6 (1σ) × AD (average displacement). S-transform analyses indicates that high-frequency slip maxima also coincide with fault geometric complexities, consistent with stress amplifications and enhanced slip variability due to geometric and kinematic interactions with neighboring faults. Rupture slip taper angles exhibit large variations (−90% to +380% with respect to the mean value) toward rupture termini and are steepest where ruptures terminate at obliquely oriented magnetic lineaments and/or lithology changes. Incremental slip approximates AD between the 10th and 90th percentiles of the SRL. The average static stress drop of the studied earthquakes is 4.8 ± 2.8 MPa. A surface rupture classification scheme for cratonic stable regions is presented to describe the prevailing characteristics of intraplate earthquakes across diverse crustal structural-geophysical settings. New scaling relationships and suggestions for logic tree weights are provided to enhance probabilistic fault displacement hazard analyses for bedrock-dominated intraplate continental regions.

Characteristics of the Seismic Clusters Bounding the Ramu-Markham Fault Zone, Eastern Papua New Guinea

ABSTRACT The regionally extensive Ramu-Markham-Fault-Zone (RMFZ) in Papua-New-Guinea (PNG) passes through the seismically-active hinterland of the Bismarck subduction zone in SW-Pacific. The seismicity map for 400km segment of RMFZ shows that higher magnitude earthquakes mainly originate in four spatial clusters (I-IV), asymmetrically disposed from in-land to offshore on either side of RMFZ. The cluster III have produced the 2019 Bulolo- earthquake (Mw 7.1). The spatial and temporal characters for all four seismic clusters was estimated by: (i) b-value based on maximum-likelihood method; (ii) expected maximum magnitude (Mw) by Gumbel extreme value statistics and surface rupture length; and (iii) the Hurst coefficient (K) and Hurst plot. Hurst plots on sequential seismic moments in the clusters illustrate an alternating positive and negative sloping moment-release pattern over progressive time-period that corresponds to low and high b-values respectively. The regional stress pattern on north and south of RMFZ and for four seismic clusters are analysed by inversion of CMT focal-mechanism data. The result unravels a significant change in regional stress pattern across the RMFZ: (i) a pure-compressive stress regime corresponding to clusters I and II in the ‘PNG Highlands’ that gradually changes to transpressive in the off-shore cluster IV along north of RMFZ, and (ii) the regional stress pattern for earthquakes south of RMFZ including cluster III shows absence of any particular stress orientation and causative faults are randomly oriented. This leads to the presentation that RMFZ is a deep penetrative fault, rather than a crustal ramp fault restricted to 11-18km depth as advocated in literature.

Constraining coseismic earthquake slip using Structure from Motion from fault scarp mapping (East Helanshan Fault, China)

This study uses fault scarps to investigate past earthquakes and the potential seismic hazard of the East Helanshan Fault (EHF). The EHF is a Holocene active normal fault located at the complex transition from compression in the northeastern corner of the Tibetan Plateau to apparently east-west extension in the west margin of Ordos Block, as implied by the Yinchuan Faulted Basin and its boundary normal faults. Repeated normal faulting events, including the 1739 CE event on the EHF, offset alluvial fans of Late Pleistocene and Holocene age and formed remarkable fault scarps, especially along its Suyukou and Hongguozi segments. We selected three fault sections in the Suyukou and Hongguozi segments, where fault scarps of different heights are well preserved on different terrace surfaces. By using Structure-from-Motion-Multiview Stereo (SfM-MVS) techniques on Unmanned Aerial System (UAS) imagery, we acquired high-quality topography of the selected fault sections. Detailed mapping and surveying of the offset geomorphic features and their associated fault scarps, with distinct free faces and multiple slope breaks, suggest that surface-rupturing earthquakes occurred repeatedly along the EHF. Densely spaced cross scarp topographic profiles were extracted to evaluate the vertical slip distributions using newly acquired SfM-derived topography. Through statistical analysis of the displacement dataset, we constrain multiple earthquake events and their cumulative offsets on the Suyukou and Hongguozi segments. Large earthquakes on the EHF produced different characteristic co-seismic slips on the Suyukou segment and the Hongguozi segment of ~2.6 m and ~1.7 m, respectively. The scaling relationships between the moment magnitude, surface rupture length, and the average co-seismic slip indicate possible magnitudes within a range of Mw 6.8–7.2, and a potential magnitude of approximately Mw 7.4 as an upper bound in the case of a multi-fault rupture along the EHF. This study demonstrates the UAS-based SfM photogrammetry as an effective means for mapping fault zone topography in areas of sparse vegetation, as well as its potential for identifying and measuring subtle geomorphic features associated with past earthquakes.

Mainshock Anticipated by Intra-Sequence Ground Deformations: Insights from Multiscale Field and SAR Interferometric Measurements

The 2016 Central Italy seismic sequence was characterized by two main events: 24 August, Mw 6, and 30 October, Mw 6.5. We carried out high-resolution field sampling and DInSAR analysis of the coseismic and intra-sequence ground deformations along the Mt Vettore-Mt Bove causative fault (VBF). We found that during the intra-sequence period (24 August–30 October), the ground experienced some deformations whose final patterns seemed to be retraced and amplified by the following mainshock. We interpreted that (i) immediately after the 24 August earthquake, the deformation observed in the southern VBF expanded northwards and westwards over a Length of Deforming Ground (LDG) ranging between 28.7 and 36.3 km, and (ii) it extended to the whole portion of the hanging wall that was later affected by mainshock coseismic deformation. Assuming the LDG to be an indicator for an expected (=coseismic) surface rupture length and using known scaling functions, we obtained 6.4 ≤ Mw ≤ 6.7 for a possible incoming earthquake, which is consistent with the mainshock magnitude. We suggest that the evolution of the ground deformations after a significant seismic event might provide insights on the occurrence of new earthquakes with magnitudes comparable to or larger than the former.

Earthquake-induced deformation structures in glacial sediments—evidence on fault reactivation and instability at the Vaalajärvi fault in northern Fennoscandia

Late and postglacial reverse faults and seismically-induced landslides are characteristic features of deglaciated terrain in the northern Fennoscandia. The main focus of this study was to investigate the rupturing history of the reverse Vaalajarvi fault complex in Sodankyla, Finland, based on remote sensing, on-site geophysics and sedimentology in excavations trenched across the faulted terrain. In addition to the previously known NNW–SSE-trending Vaalajarvi segment, we discovered six new SW–NE-trending fault segments that probably belong to the same Vaalajarvi ‘postglacial’ fault complex. Our analysis indicate that the Vaalajarvi fault segment was triggered by stress change caused by ruptures on the surrounding SW–NE-trending reverse faults. In total, at least two to three slip events have taken place in different segments of the Vaalajarvi complex since the Early Weichselian with the most recent event(s) being postglacial in timing. By using the scaling laws of fault surface rupture length and offset and under different scenarios of which segments or systems ruptured in a single or separate event, we estimate that the Vaalajarvi complex potentially hosted an earthquake that ranged between Mw ≈ 6.7–7.0. This magnitude is comparable to the landslide-inferred magnitudes in the Vaalajarvi area.

Holocene activity and seismic hazard analysis of faults in Damxung, Tibet

Based on interpretation of remote sensing and geological field survey result, three secondary faults are distributed in parallel in Damxung of the southeastern piedmont fault of Nyainqentanglha mountain, which form landform profile across normal faults of graben due to cut platform margin of grade I terrace scarp formation. Through researching the displacements and the collected sediments dates, it is obtained that the horizontal slip rate is about 0.6 mm/a (millimeter per year), and the vertical slip rate is about 1.7 mm/a since 4 ka B.P. (kilo years before present). The northern margin of Damxung basin is a seismic gap, which continuously accumulated strain energy is not released in the M7.5 Damxung earthquake and the M8.0 Yangbajain earthquake. The fracture length of the seismic space can be regarded as the minimum length of potential surface rupture. The maximum moment magnitude of potential earthquakes is at least M6.8.in northern margin of Damxung basin the normal fault magnitude estimation formulas from Wells and Coppersmith (Bull Seismol Soc Am 84(4):974–1002, 1994).

Neotectonic and Paleoseismic Analysis of the Northwest Extent of Holocene Surface Deformation along the Meers Fault, Oklahoma

ABSTRACT The Meers fault (Oklahoma) is one of few seismogenic structures with evidence for Holocene surface rupture in the stable continental region of North America. The 37-kilometer-long southeast section of the full 54-kilometer-long Meers fault is interpreted to be Holocene active. The 17-kilometer-long northwest section is considered Quaternary active, but not Holocene active. We reevaluate surface expression and earthquake timing of the northwest Meers fault to improve seismic source characterization. We use airborne light detection and ranging and historical stereopaired aerial photos to evaluate the fault scarp and local fault-zone geomorphology. In the northwest, complex surface deformation includes fault splays, subtle monoclinal warping, and a minor change in fault strike. We interpret that the along-strike transition from surface faulting on the southeast Meers fault to surface folding on the northwest Meers fault occurs at the lithologic contact between Permian Post Oak conglomerate and Hennessey shale. We excavated a paleoseismic trench to evaluate the timing of surface-deforming earthquakes on the northwest section of the fault. The excavation revealed weathered Permian Hennessey shale and an ∼1–2-meter-thick veneer of Holocene alluvial deposits that were progressively deformed during two surface-folding earthquakes likely related to blind fault rupture beneath the site. Repeated onlapping to overlapping stratigraphic sequences and associated unconformities are intimately related to folding events along the monocline. OxCal paleoearthquake age modeling indicates that earthquakes occurred 4704–3109 yr B.P. and 5955–4744 yr B.P., and that part of the northwest section of the Meers fault is Holocene active. We find the Holocene-active section of the Meers fault should be lengthened 6.1 km to the northwest, to a total Holocene-active fault length of 43 km. Empirical scaling relationships between surface rupture length and magnitude reveal that the fault could generate an Mw 7.0 earthquake.

Investigation and magnitude re‐evaluation of the 1955 Zheduotang earthquake, eastern Tibetan Plateau, China

Rupture lengths and displacements of historical earthquakes are significant components of the accurate magnitude estimates required for understanding fault behaviour and earthquake recurrence patterns. Along the Xianshuihe–Xiaojiang fault system on the eastern Tibetan Plateau, 36 large historical earthquakes have been recorded during the past ~700 years, many of which still require detailed investigation. In this study, we reinvestigated the coseismic surface rupture produced by the 1955M7.5 Zheduotang earthquake. The Zheduotang Fault, which is the source fault of the 1955 event, is one of the main faults of the central Xianshuihe fault zone, with a left‐lateral strike‐slip rate of 3.4 mm/year according to our measurements and the ages of offset terraces. High‐resolution Google Earth images and field observations reveal that the surface ruptures of this earthquake were characterized by left‐lateral offsets of gullies, animal paths, alluvial terraces, and fans. The coseismic surface rupture length caused by the 1955 earthquake could be up to ~43 km, with mainly horizontal displacements of 0.6–1.7 m. Based on empirical relationships between magnitude and coseismic surface rupture length for large earthquakes, the magnitude of the 1955 Zheduotang earthquake is re‐evaluated to beMW7.0. Our study demonstrates the necessity of re‐evaluating previous magnitude estimates of historical earthquakes in western China.

Evidence for quaternary seismic activity of the La Alberca-Teremendo fault, Morelia region, Trans-Mexican Volcanic Belt

The La Alberca-Teremendo fault is a 26 km-long, complex fault composed of an en échelon array of short crustal fault segments, belonging to the Morelia-Acambay fault system. This fault system shows parallel scarps with morphological evidence of recent activity such as drainage alteration, maximum throws of 50 m and minimum throws of 1.4 m that displace the recent soils. The fault acted as a conduit for the formation of the La Alberca de Guadalupe maar (23000 to 21000 years ago) and displaced afterwards its phreatomagmatic sequences. The paleoseismic analysis indicates that the La Alberca-Teremendo fault moved three times in the past 23000 years (age of the maar); this activity caused an average vertical displacement of 87 cm, and might have generated earthquakes with magnitudes Mw between 6.6 and 7, as well as volcano-tectonic earthquakes with magnitudes Mw between 4 and 5.5. The displacements were identified on the fault through the superposition of soils differentiated by a disconformity and an anomalous increase in the percentage of clay and organic matter. The La Alberca-Teremendo fault has dominant dip slip with a minor left-lateral component, a slip rate of 0.114 mm/year, and an average recurrence interval of 7726 ± 68 years. According to scaling relations that use the surface rupture length, if we assume that the La Alberca-Teremendo fault moves tectonically, it could generate earthquakes with maximum magnitudes of Mw between 6.7 and 7.3, however because of the active volcanic processes in the area, we could expect moderate volcano-tectonic earthquakes (Mw 4–5.5) rather than catastrophic ones.

Paleoearthquake History Along the Southern Segment of the Daliangshan Fault Zone in the Southeastern Tibetan Plateau

AbstractAssessing the seismic hazard of a fault is usually based on its record of strong earthquakes. Earthquake records with long periods of quiescence for active faults can lead to underestimates of seismic hazards, such as for the Longmenshan fault zone which produced the unanticipated 2008Mw7.9 Wenchuan earthquake. The Daliangshan fault zone has a low slip rate and has not produced any strong earthquakes in history. As a result, little is known about its paleoearthquake history, including the behavior of any strong earthquakes it might produce and the seismic hazards posed by the Daliangshan fault zone. To solve this problem, we excavated four trenches across the Jiaojihe and Butuo faults along the southern segment of the Daliangshan fault zone. The paleoseismic investigations revealed six paleoearthquakes on the Jiaojihe fault in ~20,000 years and determined another seven rupturing events on the Butuo fault in ~42,000 years. The strong earthquake history of the Jiaojihe fault has evidence of temporal clustering, while the Butuo fault exhibits a relatively periodic recurrence pattern with intervals of 1,710–2,460 years. Based on its surface rupture length and the magnitude of observed displacement, the southern segment of the Daliangshan fault zone is capable of producingM > 6.5 earthquakes. Furthermore, based on their respective slip rates and the elapsed times since the most recent events along the Jiaojihe and Butuo faults, they have accumulated seismic energy equivalent toM ~ 7.6, suggesting they pose a significant seismic hazard to the southeastern Tibetan Plateau.

Postglacial reactivation of the Suasselk\xe4 PGF complex in SW Finnish Lapland

The Suasselkä fault complex is recognized from high-resolution digital elevation models (LiDAR DEMs) as a complex of 37 surface ruptures striking SW–NE and cutting through Weichselian glacial sediments, confirming the postglacial nature of the rupturing event. The analysis of LiDAR DEMs, geophysical profiles and trenching of glacial sediments at two sites along the Suasselkä postglacial fault (PGF) system has provided evidence of earthquakes that post- and predate the Late Weichselian deglaciation. At the Suaspalo trenching site, at least two different rupture events are observed: the first one predates the deposition of the lowermost till unit and potentially dates to the Early or even pre-Weichselian. The second rupture event, on the other hand, deforms overlying tills and is thus a post-Weichselian event. Our results indicate that multiple rupturing events can take place within ‘postglacial fault complexes’, which is the second time such a characteristic has been proven for PGFs in northern Fennoscandia. Furthermore, the present results provide the first evidence of either Early or even pre-Weichselian faulting in Finland, suggesting that the same fault complexes were also active after glacial phases that predated the last glacial maximum of the Late Weichselian. These results warrant re-evaluation of the long-term seismic risk associated with the faults as the assumption of single rupture events is erroneous. Considering that the Suasselkä PGF complex is composed of four PGF systems and 37 isolated 150–7500-m-long segments, we calculated the potential moment magnitudes based on the rupture length and mean/maximum vertical displacement for each individual segment and system, taken that they potentially ruptured independently, and finally for the entire Suasselkä PGF complex. For the entire complex rupturing in a single event, the observed displacement and length of the complex yields a moment magnitude estimate of Mw ≈ 6.7–8.1. However, based on geomorphological and sedimentological evidence, we believe that this is a conservative estimate of the moment magnitude of the paleoearthquake. If isolated PGF systems are considered to have ruptured individually, the moment magnitudes estimated based on surface rupture lengths range from Mw ≈ 5.5–6.7, and based on mean and maximum cumulative displacement values, the estimated values range from Mw ≈ 6.2–7.3 and Mw ≈ 6.7–8.0, respectively. As we cannot with the available data distinguish the exact number of events, the age of events or which segments potentially ruptured at the same time, we conclude that the events that took place in the complex ranged in moment magnitude from c. Mw ≈ 5.5 to 8.1, the Mw ≈ 8.1 estimate representing conservative upper bound for the maximum moment magnitude.

Postglacial faulting near Crater Lake, Oregon, and its possible association with the Mazama caldera-forming eruption

Abstract Volcanoes of subduction-related magmatic arcs occur in a variety of crustal tectonic regimes, including where active faults indicate arc-normal extension. The Cascades arc volcano Mount Mazama overlaps on its west an ∼10-km-wide zone of ∼north-south–trending normal faults. A lidar (light detection and ranging) survey of Crater Lake National Park, reveals several previously unrecognized faults west of the caldera. Postglacial vertical separations measured from profiles across scarps range from ∼2 m to as much as 12 m. Scarp profiles commonly suggest two or more postglacial surface-rupturing events. Ignimbrite of the ca. 7.6 ka climactic eruption of Mount Mazama, during which Crater Lake caldera formed, appears to bury fault strands where they project into thick, valley-filling ignimbrite. Lack of lateral offset of linear features suggests principally normal displacement, although predominant left stepping of scarp strands implies a component of dextral slip. West-northwest–east-southeast and north-northwest–south-southeast linear topographic elements, such as low scarps or ridges, shallow troughs, and straight reaches of streams, suggest that erosion was influenced by distributed shear, consistent with GPS vectors and clockwise rotation of the Oregon forearc block. Surface rupture lengths (SRL) of faults suggest earthquakes of (moment magnitude) Mw6.5 from empirical scaling relationships. If several faults slipped in one event, a combined SRL of 44 km suggests an earthquake of Mw7.0. Postglacial scarps as high as 12 m imply maximum vertical slip rates of 1.5 mm/yr for the zone west of Crater Lake, considerably higher than the ∼0.3 mm/yr long-term rate for the nearby West Klamath Lake fault zone. An unanswered question is the timing of surface-rupturing earthquakes relative to the Mazama climactic eruption. The eruption may have been preceded by a large earthquake. Alternatively, large surface-rupturing earthquakes may have occurred during the eruption, a result of decrease in east-west compressive stress during ejection of ∼50 km3 of magma and concurrent caldera collapse.

High‐Resolution Field Mapping and Analysis of the August–October 2016 Coseismic Surface Faulting (Central Italy Earthquakes): Slip Distribution, Parameterization, and Comparison With Global Earthquakes

AbstractWe focus on the coseismic surface faulting exposed along the Mt. Vettore‐Mt. Bove fault system (VBF, central Italy), that activated during the 24 August 2016, Amatrice earthquake (Mw6.0) and soon after reactivated during the 26 October Visso (Mw5.9) and 30 October Norcia events (Mw6.5 mainshock). We systematically recognized the coseismic surface ruptures of the aforesaid earthquakes, which document the repeated surface faulting on the same seismogenic structure in close temporal succession. We surveyed 1,747 evidence of coseismic ruptures, 325 fault plane attitudes along the Vettoretto‐Redentore segment, and over 4,000 data along the entire VBF that were organized in a GIS‐database. This data set allowed us to estimate the coseismic surface rupture length (SRL), maximum (MD) and average (AD) displacement associated with the Mw6.0 and Mw6.5 events. We found that the SRL and MD associated with the former are respectively 5.8 km and 28.5 cm and AD reaches 12.7 cm. For the mainshock, the values of SRL ≥ 22 km and MD = 222 cm were measured. The cumulative, post‐30 October parameters are SRL = 30 km, MD = 240 cm, AD = 36 cm. Despite that the MD of the Mw6.0 event differs by ~1 order of magnitude respect to the mainshock MD, the two slip profiles display a similar multiscale sinuosity showing a significant control of the long‐term fault segmentation on the coseismic rupturing. Comparing the obtained coseismic parameters with literature global earthquakes data highlights some peculiarities of the 2016 central Italy surface rupture pattern, which suggest caution in applying empirical relationships to highly segmented seismogenic faults.

Paleoseismic study on the Pingdingshan-Annanba segments of the Altyn Tagh Fault based on offset clusters

Previous studies using paleoseismic trenches and numerical models proposed two different fault rupture models for the Pingdingshan-Annanba segments of the Altyn Tagh Fault, which are both poorly validated because of a lack of measurements of surface rupture displacements. In this paper, we use high-resolution satellite imagery to measure offset geomorphic markers. Taking the fault geometry into consideration, the most likely paleoseismic rupture parameters are determined by comparing the results of the cumulative offset probability densities (COPDs) and the empirical relationships of seismic parameter. The results show that the most recent earthquake (1270A.D.-1775A.D.) along the Suoerkuli segment only ruptured the Suoerkuli Valley, with a surface rupture length of 140 km, an average horizontal displacement of 3.12 m and a moment magnitude (Mw) of 7.4–7.6. The penultimate earthquake (676A.D.-1347A.D.) ruptured both the Annanba segment and part of the Suoerkuli segment with an average horizontal displacement of greater than 5 m, a surface rupture length of 120–260 km and Mw 7.4–7.8. The rupture parameters of the above two earthquakes demonstrate that the Suoerkuli and Annanba segments are individual fault segments which can rupture independently with a surface rupture length more than 100 km. The Pingdingshan double bend to the west of the Suoerkuli segment is likely to be an endpoint that inhibits the rupture propagation towards further west.

Surface and shallow subsurface structure of the Middle Kedrovaya paleoseismic rupture zone in the Baikal Mountains from geomorphological and ground-penetrating radar investigations

The 30-km-long Middle Kedrovaya (MK) paleoseismic rupture zone, on the northwestern flank of Lake Baikal, is one of most impressive late Quaternary fault scarps in the Baikal rift. The aim of this study is to reconstruct the near-surface fault geometry of the MK fault zone to clarify its past movement history and seismic potential. We applied ground penetrating radar (GPR), along with high-resolution satellite imagery and field surface observations, to analyze the structure of the upper 12–13 m of the rupture zone and to characterize the complex structural environment in three dimensions. The GPR reveals that the shallow structure of the MK zone is defined by a combination of steep and listric normal faults, which form a surface pattern of subparallel ruptures trending predominantly N30°E. Individual surface scarps range from 5 m to 2.7 km in length and are separated by gaps of a few tens of meters to several kilometers apart. The greatest width of the scarp zone is 1.9 km. The vertical displacements measured independently from surface topographic profiles and from GPR radargrams are linearly related. The height of the main footwall (head) scarp is always 0.5–2 m greater than the throw measured on the radargrams, a result of the scarp face having broadened far up the talus slope after the latest displacement event. Maximum and average vertical normal fault displacements along the main fault trace, inferred from GPR data, are 8.3 and 4.98 m respectively. Paleoearthquake magnitude M estimated from empirical regressions ranges from 6.8 to 7.6, based on equations of M vs. surface rupture length, M vs. displacement, and M vs. landslide volume. Our study of the Middle Kedrovaya paleoseismic rupture zone confirms that listric normal faulting is widespread in the shallow (<13 m) subsurface of the western margin of the North Baikal basin. However, GPR data suggest that listric faulting is confined to the unconsolidated talus deposits and probably represents the effects of downhill gravitational sliding of the talus, and perhaps of underlying shallow bedrock. This downhill (lakeward) sliding of the hanging wall is partly responsible for the large heave component of movement on the MK rupture zone and its resulting unique geomorphic expression.This paper illustrates the practicality of investigating fault surface ruptures in complex environments by integrating data gathered by geophysics (GPR in this case) and by direct geomorphological observations. Because of the loose and mobile nature of the faulted talus deposit, the current surface morphology disguises the true number of subsurface faults, the lateral extent of faulting, and the unique structure types (all visible on radargrams) that developed to accommodate coseismic surface rupture with a large heave component.

Surface ruptures following the 30 October 2016 Mw 6.5 Norcia earthquake, central Italy

ABSTRACTWe present a 1:25,000 scale map of the coseismic surface ruptures following the 30 October 2016 Mw 6.5 Norcia normal-faulting earthquake, central Italy. Detailed rupture mapping is based on almost 11,000 oblique photographs taken from helicopter flights, that has been verified and integrated with field data (>7000 measurements). Thanks to the common efforts of the Open EMERGEO Working Group (130 people, 25 research institutions and universities from Europe), we were able to document a complex surface faulting pattern with a dominant strike of N135°-160° (SW-dipping) and a subordinate strike of N320°-345° (NE-dipping) along about 28 km of the active Mt. Vettore–Mt. Bove fault system. Geometric and kinematic characteristics of the rupture were observed and recorded along closely spaced, parallel or subparallel, overlapping or step-like synthetic and antithetic fault splays of the activated fault systems, comprising a total surface rupture length of approximately 46 km when all ruptures were considered.

Late Quaternary paleoseismology of the Milin fault: Implications for active tectonics along the Yarlung Zangbo Suture, Southeastern Tibet Plateau

How the eastward motion of crust in the central Tibetan Plateau is accommodated in the remote regions of the eastern Himalayan syntaxis remains uncertain. Although the Yarlung Zangbo suture (YZS) forms a striking lineament in the topography of the region, evidence for recent faulting along this zone has been equivocal. To understand whether faults along the YZS are active, we performed a geological investigation along the eastern segments of the YZS. Geomorphic observations suggest the presence of active faulting along several segments of the YZS, which we collectively refer to as the “Milin fault”. Paleoseismologic data from trenches reveal evidence for one faulting event, which is constrained to occur between 5620 and 1945 a BP. The latest faulting event displaced alluvial surface T2 by ~7m. The offset on this earthquake place the minimum value on the vertical slip rate of ~0.3mm/yr. Empirical relationships between surface rupture length, displacement and magnitude, suggest that magnitude of the latest event could have been Mw ~7.3–7.7. On the basis of this slip rate and the elapsed time since the last event, it is estimated that a seismic moment equivalent to Mw ~7.0 has been accumulated on the Milin fault. It is pose a threat to the surrounding region. Our results suggest that shortening occurs in the vicinity of the eastern Himalayan syntaxis, and part of eastward motion of crust from the central Tibetan Plateau is absorbed by uplift of the eastern Himalayan syntaxis.

A new empirical equation proposed for the relationship between surface rupture length and the earthquake source parameters

This study aimed to investigate the effects of magnitude, focal depth and the thickness of the overburden material on the length of the surface rupture caused by an earthquake; and to propose new empirical equations between the surface rupture length and the earthquake source parameters. To accomplish this purpose, a series of tests were carried out in the laboratory utilizing a set up simulating a strike-slip faulting mechanism. In addition to laboratory tests, a database was established from the earthquakes that have occurred in Turkey and all over the world. Consequently, new empirical equations were suggested between magnitude and surface rupture length and focal depth of an earthquake based on the data obtained from the laboratory model tests and real earthquakes.

A rock fall of the north Zhongtiao Shan fault and the Yongji earthquake in 793, Shanxi Province, North China

Earthquake is the main driving factor of landslides, and a large number of empirical formulas for seismic parameters have been proposed. This article studies a rock avalanche triggered by a paleoearthquake and two trial trenches in Yongji, Shanxi Province. Six quartz samples were collected from different parts on the top of the boulder, and the youngest 10Be exposure age is 1173 ± 123 years, which is considered as the occurrence time of the rock fall. The trenches excavated near the boulder infer that there was an earthquake between 2000 ± 110 and 465 ± 45 cal a bp in the north Zhongtiao Shan (NZS) fault with a maximum vertical displacement of 1.5 m and the surface rupture length (SRL) of ~35 km corresponding to a magnitude (MS) of 6.70 ± 0.12 based on the displacement. Taking into account the occurrence time and minimum magnitude triggering the rock fall, the latest paleoearthquake revealed by trenches may be the forcing factor. Furthermore, according to historical records of Yongji, the earthquake of magnitude 6 in ad 793 is in consistency with the occurrence time and magnitude of the earthquake triggering the landslide. Therefore, the rock fall is related to the paleoearthquake revealed by the trenches, which may be the 793 Yongji earthquake.

A palaeoseismic trench investigation of early Holocene neotectonic faulting along the Kango Fault, southern Cape Fold Belt, South Africa– part II: earthquake parameters

The location and estimated magnitude of a recent surface rupturing earthquake along the eastern part of the Kango Fault traversing the southern Cape Fold Belt, South Africa, is reported here, as well as the minimum recurrence interval and maximum slip rate. These palaeoseismic data are derived from analysis of the mapped logs of an 82 m long, 5 m deep trench excavated across the fault, supported by 12 optically stimulated luminescence (OSL) dates. The tectonic event that formed the observed 2.0 ± 0.06 m free-standing fault scarp at the trench site had a moment magnitude estimated between 6.97 ± 0.01 M and 7.18 ± 0.01 M. According to the recently established Environmental Scale of Intensity, the rupture was devastating (ESI Io = XI). It would have been accompanied by strong ground shaking felt across most of South Africa by the ancestors of the indigenous people groups who experienced the well-known 6.3 M Ceres-Tulbagh event of 29 September 1969 (currently South Africa’s largest and most damaging earthquake). This latter strike-slip event occurred along the western end of the same Ceres-Kango-Baviaanskloof-Coega (CKBC) fault system, but was not accompanied by significant surface deformation. In contrast, the Kango ‘Toorwater’ earthquake reported here displaced the land surface vertically, by over 2 m in places. While the fault scarp extends laterally for at least 84 km, from near the town of De Rust, east of Oudtshoorn, towards the start of the Baviaanskloof in the Eastern Cape, it is unlikely the entire surface rupture length originated during only the most recent event. The palaeoseismic data reported here have contributed to a seismic source characterization model used to update the existing seismotectonic model for South Africa, first established in the mid-1990’s, and revised at various intervals since. The presence of a potentially active, capable, seismogenic structure within a low-seismicity intraplate stable cratonic region suggests that the current 5.3 to 6.3 M m max for the south and south eastern Cape must be reviewed, should these data be included in a revised Probabilistic Sesimic Hazard Assessment (PSHA) for critical structures in the region.