Recurrence Interval Of Earthquakes Research Articles

Seismic risk assessment and design of tourism buildings using probability analysis

The average recurrence interval of major earthquakes is approximately a century. Consequently, the existing data are insufficient for an accurate estimation of average losses. The main objective of this research is to study the disaster-prone characteristics of hotels by using modern concepts of risk management (i.e., loss exceedance probability analysis, seismic hazard analysis and so on) and then combine the relevant basic research data from domestic and foreign sources to develop a seismic risk assessment and management system suitable for the hospitality industry. The proposed seismic risk management and risk evaluation system will also provide governments, hotel asset owners, insurance companies and banks in Taiwan that have similar regional characteristics with the necessary seismic risk information to help the tourism industry effectively evaluate and manage the natural disaster risk.

Seismic hazard assessment of Koyna region, Peninsular India: using geospatial approach

BackgroundEarthquake-prone regions from the stable continental regions (like Peninsular India) warrant total seismic hazard estimation from possible sources — reservoir induced or tectonic. The Koyna region falls in the so-called stable continental region, though previously considered as aseismic because of its location in the Peninsular India, which was argued to be the continental Shield region; however, it is seismically active ever since the December 10, 1967, strong earthquake (M6.5) which killed around 200 people and damaged properties. The event was initially attributed to reservoir-induced seismicity. The present study aims at mapping the spatial distribution of hazard intensity in terms of peak ground acceleration and damage potential expressed as Modified Mercalli Intensity (MMI) levels owing to the scenario earthquakes (M4.0 to M6.9) from the linear sources and background seismicity in the Koyna region. For the seismic source model, geospatial integration approach is used. To delineate the source boundaries we perform spatial analysis of seismicity attributes and assigning weights based on the geological information. In addition, spatial buffering of thematic layers of faults and lineaments is applied to truncate the spatial uncertainties. Thematic attribute layers are integrated over the SRTM-DEM-derived geomorphic features and spatial seismicity pattern to define the possible linear seismic source zones. We employ ArcGIS® to perform geospatial analysis and to integrate thematic spatial information finally to prepare the seismic hazard and damage potential zones for the Koyna region.ResultsWe present the probabilistically estimated seismic hazard and damage potential estimates for the Koyna region. Spatial mapping of the hazard parameters is performed on Geographic Information System (GIS) platform. Along with the historical and instrumental earthquake data, we incorporate updated and relocated seismic events from circa 1618 to 2017 covering ~ 400 years period, for analyzing the mean annual rates of seismicity and earthquake recurrence intervals. The anticipated recurrence intervals of earthquakes ~ M5.5 is around 100 ± 10 years. The estimated peak ground acceleration (PGA) for 10% probability being exceeded in 50 years (i.e. 500 years of return period) is greater than 21% g is anticipated for the area located (~30 km radius) between the Koyna and Warna Reservoirs.ConclusionsThe hazard estimates for the 500 years return period earthquake scenarios (M4.0 to M6.9) are based on the bedrock level estimation. Estimated PGA-values are grouped into three categories that are relatively defined as high, moderate, and low hazard zones, respectively. Slightly damaging intensity (MMI-VII level) expected in 50 years has ~ 40% probability and PGA greater than 21% g for the area which is located between Koyna and Warna Reservoirs, which is identified as high hazard zone.

Late Holocene slip rate and average recurrence interval of great earthquakes on the Shangzhi segment of the Yilan‐Yitong Fault Zone, northeastern China: Constraints from paleo‐earthquakes and historical written records

AbstractThe Yilan‐Yitong Fault Zone (YYFZ) is considered to be the key branch of the Tancheng‐Lujiang Fault Zone (TLFZ) in northeastern China. Although the Mesozoic and early Cenozoic deformation of the YYFZ has been studied intensively over the past century, few estimates of slip rate and recurrence interval of large earthquakes in the late Quaternary, which are the two most important parameters for understanding the potential seismic hazard of this crucial structure, were obtained. Based on integrated interpretations of high resolution satellite images and detailed geologic and geomorphic mapping, linear landforms were identified, including fault scarps and troughs, along the Shangzhi segment of the YYFZ, which exceeds 25 km in length. Synthesized results of trench excavations and differential GPS measurements of terrace surfaces indicate that two events (E1, E2) occurred along the Shangzhi segment during the late Holocene, which resulted in 3.2 ±0.1 m of total vertical co‐seismic displacement with clear features of thrust motion. 14C dating of samples suggests that event E1 occurred between 440 ±30 years BP and 180 ±30 years BP and that event E2 occurred between 4 090 ±30 years BP and 3 880 ±30 years BP, which indicates that the minimum vertical slip rate of the Shangzhi segment of the YYFZ has been approximately 0.8 ±0.03 mm/year during the late Holocene. Constraints from paleo events and the slip rate suggest that the average recurrence interval of major earthquakes on the YYFZ is 3 800 ±200 years. Historical documents in Korea show that event E1 possibly corresponds to the earthquake that occurred in AD 1810 (the Qing Dynasty in Chinese history) in the Ningguta area, which had surface‐wave magnitude (Ms) of 6.8–7.5. Studies of kinematics show that the right‐lateral strike‐slip with a reverse component has been dominant along the YYFZ during the late Holocene.

Earthquake cycle simulations with rate-and-state friction and power-law viscoelasticity

We simulate earthquake cycles with rate-and-state fault friction and off-fault power-law viscoelasticity for the classic 2D antiplane shear problem of a vertical, strike-slip plate boundary fault. We investigate the interaction between fault slip and bulk viscous flow with experimentally-based flow laws for quartz-diorite and olivine for the crust and mantle, respectively. Simulations using three linear geotherms (dT/dz=20, 25, and 30K/km) produce different deformation styles at depth, ranging from significant interseismic fault creep to purely bulk viscous flow. However, they have almost identical earthquake recurrence interval, nucleation depth, and down-dip coseismic slip limit. Despite these similarities, variations in the predicted surface deformation might permit discrimination of the deformation mechanism using geodetic observations. Additionally, in the 25 and 30K/km simulations, the crust drags the mantle; the 20K/km simulation also predicts this, except within 10km of the fault where the reverse occurs. However, basal tractions play a minor role in the overall force balance of the lithosphere, at least for the flow laws used in our study. Therefore, the depth-integrated stress on the fault is balanced primarily by shear stress on vertical, fault-parallel planes. Because strain rates are higher directly below the fault than far from it, stresses are also higher. Thus, the upper crust far from the fault bears a substantial part of the tectonic load, resulting in unrealistically high stresses. In the real Earth, this might lead to distributed plastic deformation or formation of subparallel faults. Alternatively, fault pore pressures in excess of hydrostatic and/or weakening mechanisms such as grain size reduction and thermo-mechanical coupling could lower the strength of the ductile fault root in the lower crust and, concomitantly, off-fault upper crustal stresses.

Late Quaternary paleoseismicity and seismic potential of the Yilan-Yitong Fault Zone in NE China

The Yilan-Yitong Fault Zone (YYFZ), which is composed of two nearly parallel branches with a spacing of 5–30 km and a length of ∼1100 km, is considered to be the key branch of the Tancheng-Lujiang Fault Zone (TLFZ) in NE China. It was traditionally believed that the YYFZ experienced weak activity or was inactive during the Late Quaternary, without the capability to generate strong earthquakes (M ≥ 7), based on the absence of typical outcrops and large historical or instrumental earthquakes (M > 6). However, our paleoseismic study shows that the YYFZ is the primary seismotectonic structure (M ≥ 7) that poses significant earthquake threats to NE China. The synthesis of data collected from geologic investigations, geomorphic mapping, trench logging and the dating of samples indicates that the YYFZ is an active structure that has undergone segmented strong tectonic deformation since the Late Quaternary with a characteristic assemblage of landforms, including linear scarps and troughs, offset or deflected streams, linear sag ponds, small horsts and grabens. The latest ruptures of the YYFZ migrated from previous boundary faults into the basin interior, forming a left-stepping en echelon pattern in plain view, and the kinematics of these events in the Late Quaternary were dominated by reverse dextral slipping. Multi-segment cluster faulting might have occurred during three cluster periods, i.e., ∼34750–35812 a BP, ∼21700–22640 a BP, and ∼4000 a BP-present, which implies that the recurrence interval of large earthquakes along the YYFZ may be as long as tens of thousands of years.

Millennium Recurrence Interval of Morphogenic Earthquakes on the Seismogenic Fault Zone That Triggered the 2016 Mw 7.1 Kumamoto Earthquake, Southwest Japan

Millennium Recurrence Interval of Morphogenic Earthquakes on the Seismogenic Fault Zone That Triggered the 2016 Mw 7.1 Kumamoto Earthquake, Southwest Japan

Silica precipitation potentially controls earthquake recurrence in seismogenic zones

Silica precipitation is assumed to play a significant role in post-earthquake recovery of the mechanical and hydrological properties of seismogenic zones. However, the relationship between the widespread quartz veins around seismogenic zones and earthquake recurrence is poorly understood. Here we propose a novel model of quartz vein formation associated with fluid advection from host rocks and silica precipitation in a crack, in order to quantify the timescale of crack sealing. When applied to sets of extensional quartz veins around the Nobeoka Thrust of SW Japan, an ancient seismogenic splay fault, our model indicates that a fluid pressure drop of 10–25 MPa facilitates the formation of typical extensional quartz veins over a period of 6.6 × 100–5.6 × 101 years, and that 89%–100% of porosity is recovered within ~3 × 102 years. The former and latter sealing timescales correspond to the extensional stress period (~3 × 101 years) and the recurrence interval of megaearthquakes in the Nankai Trough (~3 × 102 years), respectively. We therefore suggest that silica precipitation in the accretionary wedge controls the recurrence interval of large earthquakes in subduction zones.

Paleoearthquakes on the Anninghe and Zemuhe fault along the southeastern margin of the Tibetan Plateau and implications for fault rupture behavior at fault bends on strike-slip faults

Fault bends can serve as fault segment boundaries and are used in seismic hazard assessment. Recent studies addressing whether rupture propagation would be arrested at such structural complexities have commonly focused on computational modeling. However, multi-cycle paleoseismic rupture observations through fault bends have seldom been reported. In this study, we used trenching and radiocarbon dating to reveal paleoseismic rupture histories on the southern segment of the Anninghe fault (ANHF) along the southeastern margin of the Tibetan Plateau to explore multi-cycle surface rupture behavior at an extensional fault bend (with an angle of about 30°) at Xichang between the ANHF and Zemuhe fault (ZMHF). Specifically, nine trenches were opened in a fault depression at Maoheshan site and five paleoseismic events were identified. These have been named E1 through E5 respectively corresponding to events at 1400–935BCE, 420–875CE, 830–1360CE, 1295–1715CE, and 1790CE–Present. After comparison with the historical records of earthquakes around Xichang and previous paleoseismic results, we suggest that the five seismic events are constrained at: 1365BCE–935BCE, 814CE, 950CE- 1145CE, 1536CE and 1850CE, respectively. The average recurrence interval of earthquakes along the southern segment of the ANHF is about 700–800yr. Furthermore, the evidence indicates that surface-faulting events along the southern segment of the ANHF appear to be unevenly spaced in time. Moreover, based on comparisons of seismic events along the ANHF and ZMHF, we find that two fault segments simultaneous ruptured during the 814CE and 1850CE earthquakes, event E3 and the 1536CE earthquake ruptured the ANHF but not rupture the ZMHF. We suggest that the Xichang fault bend is not a persistent fault boundary, indicating that extensional fault bends with an angle of about 30° may not effectively terminate seismic ruptures on strike-slip faults.

A 667 year record of coseismic and interseismic Coulomb stress changes in central Italy reveals the role of fault interaction in controlling irregular earthquake recurrence intervals

AbstractCurrent studies of fault interaction lack sufficiently long earthquake records and measurements of fault slip rates over multiple seismic cycles to fully investigate the effects of interseismic loading and coseismic stress changes on the surrounding fault network. We model elastic interactions between 97 faults from 30 earthquakes since 1349 A.D. in central Italy to investigate the relative importance of co‐seismic stress changes versus interseismic stress accumulation for earthquake occurrence and fault interaction. This region has an exceptionally long, 667 year record of historical earthquakes and detailed constraints on the locations and slip rates of its active normal faults. Of 21 earthquakes since 1654, 20 events occurred on faults where combined coseismic and interseismic loading stresses were positive even though ~20% of all faults are in “stress shadows” at any one time. Furthermore, the Coulomb stress on the faults that experience earthquakes is statistically different from a random sequence of earthquakes in the region. We show how coseismic Coulomb stress changes can alter earthquake interevent times by ~103 years, and fault length controls the intensity of this effect. Static Coulomb stress changes cause greater interevent perturbations on shorter faults in areas characterized by lower strain (or slip) rates. The exceptional duration and number of earthquakes we model enable us to demonstrate the importance of combining long earthquake records with detailed knowledge of fault geometries, slip rates, and kinematics to understand the impact of stress changes in complex networks of active faults.

Shear strain concentration mechanism in the lower crust below an intraplate strike-slip fault based on rheological laws of rocks

We conduct a two-dimensional numerical experiment on the lower crust under an intraplate strike-slip fault based on laboratory-derived power-law rheologies considering the effects of grain size and water. To understand the effects of far-field loading and material properties on the deformation of the lower crust on a geological time scale, we assume steady fault sliding on the fault in the upper crust and ductile flow for the lower crust. To avoid the stress singularity, we introduce a yield threshold in the brittle–ductile transition near the down-dip edge of the fault. Regarding the physical mechanisms for shear strain concentration in the lower crust, we consider frictional and shear heating, grain size, and power-law creep. We evaluate the significance of these mechanisms in the formation of the shear zone under an intraplate strike-slip fault with slow deformation. The results show that in the lower crust, plastic deformation is possible only when the stress or temperature is sufficiently high. At a similar stress level, sim100 MPa, dry anorthite begins to undergo plastic deformation at a depth around 28–29 km, which is about 8 km deeper than wet anorthite. As a result of dynamic recrystallization and grain growth, the grain size in the lower crust may vary laterally and as a function of depth. A comparison of the results with constant and non-constant grain sizes reveals that the shear zone in the lower crust is created by power-law creep and is maintained by dynamically recrystallized material in the shear zone because grain growth occurs in a timescale much longer than the recurrence interval of intraplate earthquakes. Owing to the slow slip rate, shear and frictional heating have negligible effects on the deformation of the shear zone. The heat production rate depends weakly on the rock rheology; the maximum temperature increase over 3 Myr is only about several tens of degrees.Graphical .

Sediment gravity flows triggered by remotely generated earthquake waves

AbstractRecent great earthquakes and tsunamis around the world have heightened awareness of the inevitability of similar events occurring within the Cascadia Subduction Zone of the Pacific Northwest. We analyzed seafloor temperature, pressure, and seismic signals, and video stills of sediment‐enveloped instruments recorded during the 2011–2015 Cascadia Initiative experiment, and seafloor morphology. Our results led us to suggest that thick accretionary prism sediments amplified and extended seismic wave durations from the 11 April 2012 Mw8.6 Indian Ocean earthquake, located more than 13,500 km away. These waves triggered a sequence of small slope failures on the Cascadia margin that led to sediment gravity flows culminating in turbidity currents. Previous studies have related the triggering of sediment‐laden gravity flows and turbidite deposition to local earthquakes, but this is the first study in which the originating seismic event is extremely distant (> 10,000 km). The possibility of remotely triggered slope failures that generate sediment‐laden gravity flows should be considered in inferences of recurrence intervals of past great Cascadia earthquakes from turbidite sequences. Future similar studies may provide new understanding of submarine slope failures and turbidity currents and the hazards they pose to seafloor infrastructure and tsunami generation in regions both with and without local earthquakes.

Paleoseismology and slip rate of the western Tianjingshan fault of NE Tibet, China

We present results from a detailed investigation of the horizontal displacement distribution, timing of paleoearthquakes and left-lateral slip rate on the western Tianjingshan fault. Measurements of 240 offset streams and ridges confirm that the fault is left-lateral and record evidence of repeated ∼3–4m coseismic offsets along the 60–km–long fault. This suggests that ∼6 earthquakes may have occurred along the entire western Tianjingshan fault with repeated occurrence of earthquakes of Mw 7.2–7.5. Structural and stratigraphic relationships exposed in our five trenches in combination with previously reported studies further indicate that the fault has ruptured in as many as six paleoearthquakes since the late Quaternary. Paleoseismic data show that the average recurrence interval for Holocene earthquakes is approximately 5,000yr. The most recent earthquake along the western Tianjingshan fault occurred ∼1.2±0.1kyrBP, indicating that this fault segment did not rupture in the M 7.5 historical earthquake of 1709 that ruptured the central Tianjingshan fault. We estimate that the Holocene slip rate of the western Tianjingshan fault is ∼1.1–1.2mm/yr based on measurements of the age and offset of stream channels. Compared with the relatively fast slip rate of the Haiyuan fault (∼4–6mm/yr), we suggest that the Tianjingshan fault acts as an essential active fault accommodating the sinistral displacement and crustal shortening deformation in NE Tibet.

Stratigraphic records of tsunamis along the Japan Sea, southwest Hokkaido, northern Japan

AbstractThe stratigraphy of tsunami deposits along the Japan Sea, southwest Hokkaido, northern Japan, reveals tsunami recurrences in this particular area. Sandy tsunami deposits are preserved in small valley plains, whereas gravelly deposits of possible tsunami origin are identified in surficial soils covering a Holocene marine terrace and a slope talus. At least five horizons of tsunami events can be defined in the Okushiri Island, the youngest of which immediately overlies the Ko‐d tephra layer (1640 AD) and was likely formed by the historical Oshima‐Ohshima tsunami in 1741 AD. The four older tsunami deposits, dated using accelerator mass spectrometry 14C, were formed at around the 12th century, 1.5–1.6, 2.4–2.6, and 2.8–3.1 ka, respectively. Tsunami sand beds of the 1741 AD and circa 12th century events are recognized in the Hiyama District of Hokkaido Island, but the older tsunami deposits are missing. The deposits of these two tsunamis are found together at the same sites and distributed in regions where wave heights of the 1993 tsunami (Hokkaido Nansei‐oki earthquake, Mw = 7.7) were less than 3 m. Thus, the 12th century tsunami waves were possibly generated near the south of Okushiri Island, whereas the 1993 tsunami was generated towards the north of the island. The estimated recurrence intervals of paleotsunamis, 200–1100 years with an average of 500 years, likely represents the recurrence interval of large earthquakes which would have occurred along several active faults offshore of southwest Hokkaido.

Reading a 400,000-year record of earthquake frequency for an intraplate fault

Our understanding of the frequency of large earthquakes at timescales longer than instrumental and historical records is based mostly on paleoseismic studies of fast-moving plate-boundary faults. Similar study of intraplate faults has been limited until now, because intraplate earthquake recurrence intervals are generally long (10s to 100s of thousands of years) relative to conventional paleoseismic records determined by trenching. Long-term variations in the earthquake recurrence intervals of intraplate faults therefore are poorly understood. Longer paleoseismic records for intraplate faults are required both to better quantify their earthquake recurrence intervals and to test competing models of earthquake frequency (e.g., time-dependent, time-independent, and clustered). We present the results of U-Th dating of calcite veins in the Loma Blanca normal fault zone, Rio Grande rift, New Mexico, United States, that constrain earthquake recurrence intervals over much of the past ∼550 ka-the longest direct record of seismic frequency documented for any fault to date. The 13 distinct seismic events delineated by this effort demonstrate that for >400 ka, the Loma Blanca fault produced periodic large earthquakes, consistent with a time-dependent model of earthquake recurrence. However, this time-dependent series was interrupted by a cluster of earthquakes at ∼430 ka. The carbon isotope composition of calcite formed during this seismic cluster records rapid degassing of CO2, suggesting an interval of anomalous fluid source. In concert with U-Th dates recording decreased recurrence intervals, we infer seismicity during this interval records fault-valve behavior. These data provide insight into the long-term seismic behavior of the Loma Blanca fault and, by inference, other intraplate faults.

Apparent Late Quaternary Fault‐Slip Rate Increase in the Southern Lower Rhine Graben, Central Europe

In regions of low strain, long earthquake recurrence intervals (104–106 yrs) and erosive processes limit preservation of Quaternary markers suitable for distinguishing whether faults slip at uniform or secularly varying rates. The Lower Rhine graben in the border region of Germany, The Netherlands, and Belgium provides a unique opportunity to explore Quaternary slip‐rate variations in a region of low strain using the basal (2.29±0.29 Ma) and surface (700±80 ka) contacts of the regionally extensive main terrace (“Hauptterrasse”), deposited by the Rhine and Maas Rivers. These surfaces are vertically offset 3–140 m and 0–68 m, respectively, across individual fault strands within a distributed network of northwest‐trending, slow‐slipping ( 80% of the sites record an apparent increase in slip rate for the more recent interval from 700 ka to present, which corresponds to a period of increased uplift of the nearby Rhenish Massif and regional volcanism. However, the apparent increase in slip rate could result, in part, from erosion of the footwall surface below the main terrace, leading to an apparent displacement that is smaller than the total vertical offset since the start of the Quaternary. Prior work focused on characterization of these faults as seismic sources in the Lower Rhine graben has preferentially relied on the average fault‐slip rate constrained using the base of the main terrace. We suggest that average fault‐slip rates calculated using the ∼700 ka main terrace surface are subjected to fewer uncertainties and sample a time interval that is more relevant for seismic‐hazard analysis. [Electronic Supplement:][1] Table of main terrace surface and basal contact offset measurements, figure describing an unrealistic faulting scenario, and a KML file with the fault‐trace mapping spanning the Lower Rhine graben. [1]: http://www.bssaonline.org/lookup/suppl/doi:10.1785/0120160197/-/DC1

Paleoearthquake history of the Spili fault

The paleoearthquake activity on the Spili Fault is examined using a novel methodology that combines measurements of Rare Earth Elements (REE) and of in situ cosmogenic 36Cl on the exhumed fault scarp. Data show that the Spili Fault is active and has generated a minimum of five large-magnitude earthquakes over the last ~16500 years. The timing and, to a lesser degree, the slip-size of the identified paleoearthquakes was highly variable. Specifically, the two most recent events occurred between 100 and 900 years BP producing a cumulative displacement of 3.5 meters. The timing of the three older paleoearthquakes is constraint at 7300, 16300 and 16500 years BP with slip sizes of 2.5, 1.2 and 1.8 meters, respectively. The magnitude of the earthquakes that produced the measured co-seismic displacements, ranges from M 6.3-7.3 while the average earthquake recurrence interval on the Spili Fault is about 4200 years. The above data suggest that the Spili is among the most active faults on Crete and its earthquake parameters may be incorporated into the National Seismic Hazard Model.

A morphologic proxy for debris flow erosion with application to the earthquake deformation cycle, Cascadia Subduction Zone, USA

In unglaciated steeplands, valley reaches dominated by debris flow scour and incision set landscape form as they often account for >80% of valley network length and relief. While hillslope and fluvial process models have frequently been combined with digital topography to develop morphologic proxies for erosion rate and drainage divide migration, debris-flow-dominated networks, despite their ubiquity, have not been exploited for this purpose. Here, we applied an empirical function that describes how slope-area data systematically deviate from so-called fluvial power-law behavior at small drainage areas. Using airborne LiDAR data for 83 small (~1 km2) catchments in the western Oregon Coast Range, we quantified variation in model parameters and observed that the curvature of the power-law scaling deviation varies with catchment-averaged erosion rate estimated from cosmogenic nuclides in stream sediments. Given consistent climate and lithology across our study area and assuming steady erosion, we used this calibrated denudation-morphology relationship to map spatial patterns of long-term uplift for our study catchments. By combining our predicted pattern of long-term uplift rate with paleoseismic and geodetic (tide gauge, GPS, and leveling) data, we estimated the spatial distribution of coseismic subsidence experienced during megathrust earthquakes along the Cascadia Subduction Zone. Our estimates of coseismic subsidence near the coast (0.4 to 0.7 m for earthquake recurrence intervals of 300 to 500 years) agree with field measurements from numerous stratigraphic studies. Our results also demonstrate that coseismic subsidence decreases inland to negligible values >25 km from the coast, reflecting the diminishing influence of the earthquake deformation cycle on vertical changes of the interior coastal ranges. More generally, our results demonstrate that debris flow valley networks serve as highly localized, yet broadly distributed indicators of erosion (and rock uplift), making them invaluable for mapping crustal deformation and landscape adjustment.

Characterization of slow slip rate faults in humid areas: Cimandiri fault zone, Indonesia

AbstractIn areas where regional tectonic strain is accommodated by broad zones of short and low slip rate faults, geomorphic and paleoseismic characterization of faults is difficult because of poor surface expression and long earthquake recurrence intervals. In humid areas, faults can be buried by thick sediments or soils; their geomorphic expression subdued and sometimes undetectable until the next earthquake. In Java, active faults are diffused, and their characterization is challenging. Among them is the ENE striking Cimandiri fault zone. Cumulative displacement produces prominent ENE oriented ranges with the southeast side moving relatively upward and to the northeast. The fault zone is expressed in the bedrock by numerous NE, west, and NW trending thrust‐ and strike‐slip faults and folds. However, it is unclear which of these structures are active. We performed a morphometric analysis of the fault zone using 30 m resolution Shuttle Radar Topography Mission digital elevation model. We constructed longitudinal profiles of 601 bedrock rivers along the upthrown ranges along the fault zone, calculated the normalized channel steepness index, identified knickpoints and use their distribution to infer relative magnitudes of rock uplift and locate boundaries that may indicate active fault traces. We compare the rock uplift distribution to surface displacement predicted by elastic dislocation model to determine the plausible fault kinematics. The active Cimandiri fault zone consists of six segments with predominant sense of reverse motion. Our analysis reveals considerable geometric complexity, strongly suggesting segmentation of the fault, and thus smaller maximum earthquakes, consistent with the limited historical record of upper plate earthquakes in Java.

Assessing the activity of faults in continental interiors: Palaeoseismic insights from SE Kazakhstan

The presence of fault scarps is a first-order criterion for identifying active faults. Yet the preservation of these features depends on the recurrence interval between surface rupturing events, combined with the rates of erosional and depositional processes that act on the landscape. Within arid continental interiors single earthquake scarps can be preserved for thousands of years, and yet the interval between surface ruptures on faults in these regions may be much longer, such that the lack of evidence for surface faulting in the morphology may not preclude activity on those faults. In this study we investigate the 50 km-long ‘Toraigyr’ thrust fault in the northern Tien Shan. From palaeoseismological trenching we show that two surface rupturing earthquakes occurred in the last 39.9±2.7 ka BP, but only the most recent event (3.15–3.6 ka BP) has a clear morphological expression. We conclude that a landscape reset took place in between the two events, likely as a consequence of the climatic change at the end of the last glacial maximum. These findings illustrate that in the Tien Shan evidence for the most recent active faulting can be easily obliterated by climatic processes due to the long earthquake recurrence intervals. Our results illustrate the problems related to the assessment of active tectonic deformation and seismic hazard assessments in continental interior settings.

Spatiotemporal evolution of fault slip rates in deforming continents: The case of the Great Basin region, northern Basin and Range province

Compilation and synthesis of neotectonic data from the Great Basin region (western U.S.), based on 173 published studies for 171 faults across the region, offer an unprecedented view into the spatiotemporal evolution of strain release in continental domains, at time scales of 1 k.y. to 1 m.y. The results indicate a mean vertical surface displacement for normal faulting earthquakes of 2 m (approximately two-thirds of events in the 1–3 m range). The distribution of earthquake recurrence intervals is more scattered, with a mode of 1–3 k.y., a mean of 11 k.y., and 15% of recurrence intervals >20 k.y. While strike-slip faults nearest the plate boundary show relatively steady slip rates through time, northern Great Basin normal faults have had marked temporal slip-rate variations in the Quaternary. Since 15 ka, strain release has been concentrated near the margins (fault slip rates to 1–2 mm/yr), with the central region being nearly inactive. However, over the past 150 k.y., finite deformation is more evenly distributed as faults show more uniform slip rates (0.2–0.3 mm/yr) consistent with their long-term rates. The paleo-earthquake distribution since ca. 60 ka shows two kinematic patterns: local clusters (episodes of events repeated on a single fault) and regionally distributed faulting (episodes of events distributed across several parallel faults, each with a single event). We thus propose a model for northern Great Basin normal faults where they alternate between (1) transient fast periods (1–2 mm/yr) lasting ∼50 k.y., characterized by local clusters; and (2) transient slow periods (0.05–0.1 mm/yr) lasting 200–400 k.y., characterized by regional distributed faulting.