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Propagating earthquakes must overcome geometrical complexity on fault networks to grow into large, surface rupturing events. We map step‐overs, bends, gaps, splays, and strands of length scales ∼100–500 m from the surface ruptures of 31 strike‐slip earthquakes, recording whether ruptures propagated past the feature. We find that step‐overs and bends can arrest rupture and develop a statistical model for passing probability as a function of geometry for each group. Step‐overs wider than 1.2 km, single bends larger than 32°, and double bends larger than 38° are breached by rupture half of the time. ∼20% of the ruptures terminate on straight segments. We examine how the distribution of geometrical complexity influences surface rupture length, inferring an exponential relationship between rupture length and event probability. Our findings support that geometrical complexity helps limit the size of large events and provide insights into the competition between energy supply and dissipation during rupture propagation. Plain Language Summary: Zones of geometrical complexity along faults can behave as barriers that halt propagating earthquakes. We map five types of geometrical complexities from historical surface rupture maps and regional fault maps: step‐overs, bends, gaps, splays, and strands at 1:50,000 scale, corresponding to features >100–500 m in length. This is a finer scale than previous studies, which focused on kilometer‐scale zones of geometrical complexity. We classify each mapped zone of geometrical complexity as breached (earthquake propagated past) or unbreached (earthquake halted) and measure the width of step‐overs and strands, the length of gaps, and the angle of splays and bends. Based on these measurements, we model the probability that each feature will be breached given its geometry. Step‐overs wider than 1.2 km, single bends larger than 32°, and double bends larger than 38° are breached by rupture half of the time. ∼20% of the ruptures terminate on straight segments. Using our probabilities, we show that the presence and geometry of features in the 100–500 m length scale plays a first‐order control on the low likelihood of large surface rupturing earthquakes. Key Points: We map step‐overs, bends, gaps, splays, and strands from surface ruptures at 1:50,000 scale and assess their potential as rupture barriersStep‐overs wider than ∼1.2 km and bends >30° consistently halt propagating rupturesOur findings support that geometrical complexity on the fault partly limits the size of large earthquakes [ABSTRACT FROM AUTHOR]

Abstract The Mw 6.4 and 6.8 Guanshan-Chihshang earthquakes occurred on 17 and 18 September 2022 resulted in prominent surface ruptures within the Longitudinal Valley in eastern Taiwan, particularly along the Yuli fault. Approximately 18 h after the mainshock, we began to document the surface rupture near Yuli Town. Our result suggests the surface rupture formed a confined single left-lateral trace in the town of Yuli, characterized by a series of en échelon right-stepping left-lateral faulting geometry. The rupture of 2022 roughly matches the locations of 1951 surface ruptures inside Yuli Town, with a similar amount of left-lateral cross-fault displacement. North and South of the Yuli residential area, we identified several sections of the surface rupture distributed in the water-saturated paddy fields. The maximum left-lateral displacement recorded across the rupture can reach 1.4 m just south of Yuli, with the fault scarp resembling a high-angle west-dipping fault geometry. In addition to the co-seismic surface ruptures, our repeating cross-fault measurements show significant post-seismic shallow after-slip along the Yuli fault. The amount of post-seismic deformation within 3 months after the mainshock is close to, or even higher than the co-seismic cross-fault displacement, consistent with local witness accounts and post-event field photos which showed continuous damage and displacement of building floors and roads after the earthquake. Such shallow post-seismic slips were also observed along the main fault trace in the 2014 South Napa earthquake, and likely represent the shallow elastoplastic behavior of the sub-vertical fault in the young alluvial sediments.

The Mw 6.4 and 6.8 Guanshan-Chihshang earthquakes occurred on 17 and 18 September 2022 resulted in prominent surface ruptures within the Longitudinal Valley in eastern Taiwan, particularly along the Yuli fault. Approximately 18 h after the mainshock, we began to document the surface rupture near Yuli Town. Our result suggests the surface rupture formed a confined single left-lateral trace in the town of Yuli, characterized by a series of en échelon right-stepping left-lateral faulting geometry. The rupture of 2022 roughly matches the locations of 1951 surface ruptures inside Yuli Town, with a similar amount of left-lateral cross-fault displacement. North and South of the Yuli residential area, we identified several sections of the surface rupture distributed in the water-saturated paddy fields. The maximum left-lateral displacement recorded across the rupture can reach 1.4 m just south of Yuli, with the fault scarp resembling a high-angle west-dipping fault geometry. In addition to the co-seismic surface ruptures, our repeating cross-fault measurements show significant post-seismic shallow after-slip along the Yuli fault. The amount of post-seismic deformation within 3 months after the mainshock is close to, or even higher than the co-seismic cross-fault displacement, consistent with local witness accounts and post-event field photos which showed continuous damage and displacement of building floors and roads after the earthquake. Such shallow post-seismic slips were also observed along the main fault trace in the 2014 South Napa earthquake, and likely represent the shallow elastoplastic behavior of the sub-vertical fault in the young alluvial sediments. Key points: We documented surface ruptures and cross-fault displacements in the vicinity of Yuli after the 2022 Guanshan-Chihshang earthquakes. The surface ruptures in Yuli showed clear left-lateral displacements along the previously mapped Yuli fault that ruptured in November 1951. Rapid and persisted after-slip was observed along this section of the Yuli fault trace. [ABSTRACT FROM AUTHOR]

The macroseismic intensity of the February 6, 2012, Negros Oriental earthquake (MW 6.7), which affected the islands of Negros and Cebu, central Philippines, has been reassessed in this study using the Environmental Seismic Intensity Scale (ESI-2007). This earthquake caused a ∼75-km-long surface rupture along a previously unmapped fault and resulted in extensive landslides, localized liquefaction, lateral spreading, a tsunami, and widespread damage to infrastructure near the epicentral area. Considering the widespread earthquake environmental effects (EEEs), ESI-2007 intensities were evaluated for 324 locations covering an area of approximately 1000 km2 within the Negros and Cebu Islands. A systematic comparison was conducted between the ESI-2007 scale and the traditional intensity scales (PHIVOLCS earthquake intensity scale (PEIS) and Modified Mercalli Intensity scale (MM) along with the generation of an ESI-2007 shake map, which is solely based on site-specific ESI-2007 intensity values. According to the ESI-2007 scale, the epicentral intensity I0=X is assessed. This is two degrees higher than the intensity of the PEIS, and three degrees higher than the modified MM intensity provided by the United States Geological Survey (USGS). The intensity difference may also be due to the lack of suitable observations of building damage data in this sparsely populated region of the Philippines. Comparison of the ShakeMap that was constructed using the ESI-2007 intensities with the PHIVOLCS and USGS ShakeMap suggests that the instrumental or structural damage-based intensity maps underestimate the seismic intensity for the 2012 Negros Oriental earthquake. The ESI-2007 ShakeMap presented in this work is pertinent for the assessment of future seismic risk associated with other earthquake generators in the vicinity of the islands of Negros and Cebu. It can be integrated with the PEIS or MM intensity scale to improve disaster management and planning, post-earthquake recovery efforts, and damage estimation.

Abstract Propagating earthquakes must overcome geometrical complexity on fault networks to grow into large, surface rupturing events. We map step‐overs, bends, gaps, splays, and strands of length scales ∼100–500 m from the surface ruptures of 31 strike‐slip earthquakes, recording whether ruptures propagated past the feature. We find that step‐overs and bends can arrest rupture and develop a statistical model for passing probability as a function of geometry for each group. Step‐overs wider than 1.2 km, single bends larger than 32°, and double bends larger than 38° are breached by rupture half of the time. ∼20% of the ruptures terminate on straight segments. We examine how the distribution of geometrical complexity influences surface rupture length, inferring an exponential relationship between rupture length and event probability. Our findings support that geometrical complexity helps limit the size of large events and provide insights into the competition between energy supply and dissipation during rupture propagation.

On 15 January 2023, a shallow, moderate earthquake with a magnitude (Mw) of 4.7 and a depth of one kilometer struck the northern part of Leyte Island in the central Philippines. Originating along the northern Leyte segment of the Philippine Fault, a well-established creeping fault, the earthquake caused significant geologic, structural, and socio-economic impacts despite its low magnitude. Probable surface rupture and landslides were reported, leading to a comprehensive field investigation. Our investigation revealed an ~8 km discontinuous surface rupture along the northern Leyte segment of the Philippine Fault, with a maximum left-lateral displacement of 2 cm. This was the first documented occurrence of such a phenomenon associated with an earthquake of a magnitude less than 6, particularly along a creeping fault segment. The maximum ground shaking felt was reported on the PHIVOLCS Earthquake Intensity Scale (PEIS) to be VI (very strong), equivalent to a Modified Mercalli Intensity (MMI) of VI along the fault strike. However, strong motion accelerographs recorded a peak ground acceleration (PGA) of 0.407 g, equivalent to PEIS VIII (very destructive), attributed to local site amplification influenced by subsurface geology. In the area where the local site amplification occurred, limited liquefaction was observed on marshlands with recent and alluvial deposits. Two landslides were observed in the mountainous area west of the fault. Structural damages were noted in areas with PEIS VI intensity and areas transected by the surface rupture. Despite the earthquake's low magnitude, the event documented significant impacts, including surface ruptures, liquefaction, landslides, and severe structural damage. The peculiarities of this event are attributed to the shallowness of the earthquake source, and local site conditions, including geology, geomorphology, and soil properties, contributed to the severity of the impacts. Moderate in size, this earthquake emphasizes the importance of documenting moderate-sized earthquakes as a tool and guide for medium- and long-term earthquake risk assessment and resiliency. [ABSTRACT FROM AUTHOR]

The Garzê-Yushu fault is a large active NW-trending strike-slip fault on the Tibetan Plateau, along which strong earthquakes have frequently occurred historically. Together with the Xianshuihe fault, the Garzê-Yushu fault constitutes the northern boundary of the Sichuan-Yunnan block, and it is also the boundary between the Bayan Har and Qiangtang blocks. The Abuduo fault is a near E-W-trending fault on the southern side of the Garzê-Yushu fault. Through remote sensing image interpretation and field seismic geological investigations, this study found a series of left-lateral displacement landforms and well-preserved seismic surface rupture zones along the Abuduo fault, extending over a distance of approximately 65 km from Abuduo through Yushu and Qinghai to Selikou Village. According to the geological and geomorphological evidence, the Abuduo fault is considered a left-lateral strike-slip fault with Holocene activity, which has tectonic conditions suitable for breeding and generating strong earthquakes. Additionally, the eastward extension of the Abuduo fault is likely to intersect the Garzê-Yushu fault and thereby decompose its horizontal sliding deformation. [ABSTRACT FROM AUTHOR]

Three devastating and powerful earthquakes hit the southeastern and eastern parts of Türkiye and the northestern part of Syria in February of 2023, causing many earthquake-induced slope movements. One of these major mass movements is called the "Tepehan Rockslide", which was formed by the first Mw: 7.8 earthquake on February 6th, 2023 at Pazarcık (Kahramanmaraş) located in the Altınözü district of Hatay province. The rockslide involved the movement of Middle Miocene basement rocks that consist of clayey limestone, marl, and fine-grained clastic sedimentary rocks. The morphogenetic evaluation of the structure reveals that the Tepehan Rockslide is a very rapidly developed translational interrupted ridge type earthquake-induced large-scale rockslide or a large rock glide that was formed at a distance of 19 km from the surface rupture and 136 km from the earthquake epicentre. Field observations and centimeter-precise numerical data via high resolution Unmanned Aerial Vehicle (UAV) footage with a GNSS-RTK mounted module reveal that the approximately E-W oriented longest axis of the structure is 496 m, and the widest profile is 184 m, extending in N-S direction. The total moving mass has been calculated to cover ca. 71,000 m2 surface area, with an average volume of at least 1.1 million m3 and total a weight of 2.75 megatons. Comparisons made with its counterparts worldwide show that the Tepehan Rockslide is not a unique earthquake-induced slope movement by itself. However, it is the largest of the detected voluminous rockslide type slope movements formed in the region during the February 2023 earthquakes. [ABSTRACT FROM AUTHOR]

On the 6th of February 2023, Mw 7.7 Pazarcık (Kahramanmaraş) and Mw 7.6 Ekinözü (Kahramanmaraş) earthquakes that occurred in Türkiye are devastating earthquake series that filled the existing seismic gaps on East Anatolian Fault Zone on the same day. The first Mw 7.7 earthquake caught most people in their sleep and 9 h later, a second one was triggered, ending up with more than 50k death toll, widespread damage to buildings, and massive landslides. This study presents the surface rupture geometry and coseismic displacement characteristics determined with field observations immediately after February 6, 2023, Ekinözü (Kahramanmaraş, Türkiye) earthquake (Mw 7.6). Preliminary implications show that the total rupture length is 130 ± 10 km on the Çardak segment and Doğanşehir segment, known as the northern branch of the East Anatolian Fault Zone. Left lateral strike-slip faulting is developed with a maximum horizontal displacement of 6.60 m and an average displacement of 3.00 m. Furthermore, the pitches of slip lines ranging from 0° to 10° were measured on the neoformed fault planes. In addition to that, surface rupture exhibits restraining bends and releasing bends structure at small scales on the Çardak segment. From this point on, our preliminary results signify that Çardak and Doğanşehir segments were consecutively broken in Mw 7.6 Ekinözü (Kahramanmaraş) earthquake that traced between Göksun and Nurhak region and from there reached the Eskiköy regions. Furthermore, potential stress may be concentrated on not only the Sürgü segment which is on the transfer fault between the northern branch and the southern branch of East Anatolian Fault Zone but also the west of the Çardak segment and the northeast of the Doğanşehir segment near Yeşilyurt (Malatya). [ABSTRACT FROM AUTHOR]

Abstract Fault maturity has been proposed to exert a first order control on earthquake rupture, yet direct observations linking individual rupture to long‐term fault growth are rare. The 2021 Mw 7.4 Maduo earthquake ruptured the east‐growing end of the slow‐moving (∼1 mm/yr) Jiangcuo fault in north Tibet, providing an opportunity to examine the relation between rupture characteristics and fault structure. Here we combine field and multiple remote sensing techniques to map the surface rupture at cm‐resolution and document comprehensively on‐fault offsets and off‐fault deformation. The 158 km‐long surface rupture consists of misoriented structurally inherited N110°‐striking segments and younger optimally oriented N093°‐striking segments, relative to the regional stress field. Despite being comparatively newly formed, the ∼N093°‐striking fault segments accommodate more localized strain, with up to 3 m on‐fault left‐lateral slip and 25%–50% off‐fault deformation, and possibly faster rupture speed. These results are in contrast with previous findings showing more localized strain and faster rupture speed on more mature fault segments; instead, our observations suggest that fault orientation with respect to the regional stress can exert a more important control than fault maturity on coseismic rupture behavior when both factors are at play.

The Garzê–Yushu fault is a large active NW-trending strike-slip fault on the Tibetan Plateau, along which strong earthquakes have frequently occurred historically. Together with the Xianshuihe fault, the Garzê–Yushu fault constitutes the northern boundary of the Sichuan–Yunnan block, and it is also the boundary between the Bayan Har and Qiangtang blocks. The Abuduo fault is a near E–W-trending fault on the southern side of the Garzê–Yushu fault. Through remote sensing image interpretation and field seismic geological investigations, this study found a series of left-lateral displacement landforms and well-preserved seismic surface rupture zones along the Abuduo fault, extending over a distance of approximately 65 km from Abuduo through Yushu and Qinghai to Selikou Village. According to the geological and geomorphological evidence, the Abuduo fault is considered a left-lateral strike-slip fault with Holocene activity, which has tectonic conditions suitable for breeding and generating strong earthquakes. Additionally, the eastward extension of the Abuduo fault is likely to intersect the Garzê–Yushu fault and thereby decompose its horizontal sliding deformation.

This article reflects on the management of active fault surface rupture hazard after the Canterbury and Kaiköura earthquakes. To understand mitigation barriers, interviews were conducted with planners and natural hazard risk specialists in selected districts with active faults, but without land use provisions. The interviews revealed issues with the interpretation and implementation of the Ministry for the Environment's Active Fault Guidelines, Planning for Development of Land on or Close to Active Faults: a guideline to assist resource management planners in New Zealand. The purpose and intended use of the New Zealand Active Faults Database (NZAFD) is also explored. [ABSTRACT FROM AUTHOR]

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ABSTRACTWe present a 1:200,000 scale map of the Ar-Hötöl surface rupture along the Khovd fault (Mongolian Altay), presumed to be the expression of the 1761 CE Mw ∼ 7.8 Great Mongol earthquake. The detailed mapping combines airborne and terrestrial imaging and topographic techniques (Sentinel-2, Pleiades, TanDEM-X, UAV and TLS) to quantify right-lateral and vertical offsets ranging from ∼ 1 m to ∼ 4 km over a length of 238 km. The smaller offsets document the deformation associated with the last surface-rupturing earthquake that affects several Bronze to Iron Age burial mounds. Their analysis yields a robust segmentation model comprising 6 segments of 20 to 51 km in length, a maximum co-seismic slip value of 4.8 m ± 0.5 m located near the center of the rupture. Our observations precise the varying kinematics along strike, bring new evidence of repeated faulting and confirm a Mw of 7.8 ± 0.3.

On 8 January 2022, a seismic event of significant magnitude (Mw 6.7, Ms 6.9) occurred in the northeastern region of the Tibetan Plateau. This earthquake was characterized by left-lateral strike-slip motion, accompanied by a minor reverse movement. The Menyuan earthquake resulted in the formation of two main ruptures and one secondary rupture. These ruptures were marked by a left-lateral step zone that extended over a distance of 1 km between the main ruptures. The length of the rupture zones was approximately 37 km. The surface rupture zone exhibited various features, including left-lateral offset small gullies, riverbeds, wire fences, road subgrades, mole tracks, cracks, and scarps. Through a comprehensive field investigation and precise measurement using unmanned aerial vehicle (UAV) imagery, 111 coseismic horizontal offsets were determined, with the maximum offset recorded at 2.6 ± 0.3 m. The analysis of aftershocks and the findings from the field investigation led to the conclusion that the earthquake was triggered by the Lenglongling fault and the Tuolaishan fault. These faults intersected at a release double-curved structure, commonly referred to as a stepover. During this particular process, the Lenglongling fault was responsible for initiating the coseismic rupture of the Sunan–Qilian fault. It is important to note that the stress applied to the Tuolaishan fault has not been fully relieved, indicating the presence of potential future hazards. [ABSTRACT FROM AUTHOR]

Since the initial partial impoundment of the Baihetan Hydropower Station in Jinsha River watershed in early April 2021, many landslides have started undergoing rapid deformation. The Wangjiashan landslide has been the most active and dangerous landslide in the Baihetan Reservoir area. Based on road deformation data, the overall average displacement rate of the landslide before impoundment was estimated to be in the range of 11–14 cm/year. After impoundment, particularly after the water level rose to approximately 790 m above sea level (asl) between September to October 2021, the average displacement rate at various monitoring sites ranged from 200 to 600 mm/day, and the maximum value was 1002.6 mm/day. When the water level decreased to approximately 796 m asl, the landslide displacement rate immediately decreased to a range of 2–3 mm/day. The deformation of the Wangjiashan landslide was positively correlated with the rise in water level. The landslide mechanism before impoundment was active–passive failure, and soil mass damage accumulated in the transition zone (Prandtl wedge) between the active and passive blocks. The landslide was strongly affected following reservoir impoundment, with the failure mechanism transforming into a composite active–passive impoundment-accompanied failure. Under the high water level during partial impoundment in 2021, the soil mass in the transition zone of the landslide had yielded and was already in the critical sliding failure stage. Studying the Wangjiashan landslide is significant to understand the response of reservoir-induced landslides in Jinshajiang River valley and similar reservoir-induced landslides around the world. [ABSTRACT FROM AUTHOR]

On March 23, 2021 (21:14 universal time coordinated), an Mw 5.3 earthquake occurred in Baicheng County in Xinjiang, northwestern China, according to the United States Geological Survey. The earthquake produced a 4-km-long surface rupture at the epicenter, which is generally rare for earthquakes of magnitude 5.3. Thus, investigating the Baicheng earthquake is crucial for understanding the seismogenic structure of the region. We obtained the interferometric synthetic aperture radar deformation field and inverted the slip distribution of the Baicheng earthquake using Sentinel-1A satellite data and surface rupture data. The results indicate that the surface deformation area was elliptical, with long and short axes of approximately 20 and 10 km, respectively. The seismogenic structure is a left-lateral strike-slip fault with a small dip-slip component and strike and dip angles of 248° and 70°, respectively. Two other slip centers were also observed at 2 and 8 km beneath the surface in the dip direction. The maximum slip at 2 km was 0.45 m. Shear deformation between the Tarim Basin and Southern Tianshan Mountains was responsible for the strike-slip features of the Baicheng earthquake.

The 4.9 Mw earthquake of 11 November 2019 at Le Teil (France) occurred at a very shallow depth (about 1 km), inducing the surface rupture of La Rouvière fault. The question was raised shortly after about the potential impact of a nearby surface quarry. Thanks to satellite differential interferometry, here, we revealed the existence of a secondary surface rupture of the quasi-parallel Bayne Rocherenard fault. A newly processed seismic cross-section allowed us to shape the three-dimensional geometry of the local three-fault system. Assuming that the earthquake was triggered by the impact of meteoric water recharge, our numerical simulations show that the hydraulic pressure gradient at depth was at a maximum during the period of 2010–2019, just before the seismic event. The estimated overpressure at the intersection of the two faults, which is the most probable place of the hypocenter, was close to 1 MPa. This hydraulic effect is about two and a half times larger than the cumulative effect of mechanical stress release due to the mass removal from the surface quarry over the two past centuries. This work suggests a rapid hydraulic triggering mechanism on a network of faults at a shallow depth after a heavy rainfall episode. [ABSTRACT FROM AUTHOR]

On 15 January 2023, a shallow, moderate earthquake with a magnitude (Mw) of 4.7 and a depth of one kilometer struck the northern part of Leyte Island in the central Philippines. Originating along the northern Leyte segment of the Philippine Fault, a well-established creeping fault, the earthquake caused significant geologic, structural, and socio-economic impacts despite its low magnitude. Probable surface rupture and landslides were reported, leading to a comprehensive field investigation. Our investigation revealed an ~8 km discontinuous surface rupture along the northern Leyte segment of the Philippine Fault, with a maximum left-lateral displacement of 2 cm. This was the first documented occurrence of such a phenomenon associated with an earthquake of a magnitude less than 6, particularly along a creeping fault segment. The maximum ground shaking felt was reported on the PHIVOLCS Earthquake Intensity Scale (PEIS) to be VI (very strong), equivalent to a Modified Mercalli Intensity (MMI) of VI along the fault strike. However, strong motion accelerographs recorded a peak ground acceleration (PGA) of 0.407 g, equivalent to PEIS VIII (very destructive), attributed to local site amplification influenced by subsurface geology. In the area where the local site amplification occurred, limited liquefaction was observed on marshlands with recent and alluvial deposits. Two landslides were observed in the mountainous area west of the fault. Structural damages were noted in areas with PEIS VI intensity and areas transected by the surface rupture. Despite the earthquake’s low magnitude, the event documented significant impacts, including surface ruptures, liquefaction, landslides, and severe structural damage. The peculiarities of this event are attributed to the shallowness of the earthquake source, and local site conditions, including geology, geomorphology, and soil properties, contributed to the severity of the impacts. Moderate in size, this earthquake emphasizes the importance of documenting moderate-sized earthquakes as a tool and guide for medium- and long-term earthquake risk assessment and resiliency.

The typical earthquake hazards chain includes main shock, surface ruptures, aftershocks, and earthquake-induced landslides, leading to structural damage and casualties. Lots of investigation and research were published. But there is no Web-GIS platform to integrate earthquake hazards chain data and compare relative research results. This paper studies compiling such a hazards chain database and building a cloud-based Web-GIS system of the 2008 earthquake. The system introduced by this paper provides buttons and tools to browse, query and analyze map data. In addition, this system is open to anyone to add data for viewing and comparing in the web map. The result showcases that the cloud-based system runs efficiently and flexibly. The multi-scale and multi-source data can be integrated into a “one-map” system by well-design map services and geodatabase.

The Ezinepazarı Fault (EPF) is an active segment that restricts the Niksar Basin in the central part of the North Anatolian Fault Zone and has been the source of the devastating Mw 8.0 earthquake in the last 100 years. Traces of the surface rupture of the EPF, which occurred in AD 1939, can still be observed in the field today as a right-lateral strike-slip character. While paleoseismological studies were mostly focused on the western part of the North Anatolian Fault Zone (NAFZ) in previous studies, the studies on the central and eastern parts of the NAFZ are rarely addressed. In this context, trench-based paleoseismology studies were carried out on the surface rupture traces in order to determine both historical/prehistoric earthquakes caused by the fault and the Quaternary period characteristics of the EPF. According to the data obtained, at least two historical earthquake activities have been detected besides the last 1939 earthquake on the EPF. Accordingly, the first and second events occurred in E1: 5871 ± 2300 BP and E2: 1651 ± 128 BP, respectively. When the determined data are compared with the historical earthquake catalogs, it is concluded that Event 2 (E2) can be correlated with the AD 343 Niksar earthquake; thus, the EPF has an irregular earthquake recurrence interval. [ABSTRACT FROM AUTHOR]

We present a 1:200,000 scale map of the Ar-Hötöl surface rupture along the Khovd fault (Mongolian Altay), presumed to be the expression of the 1761 CE Mw ∼ 7.8 Great Mongol earthquake. The detailed mapping combines airborne and terrestrial imaging and topographic techniques (Sentinel-2, Pleiades, TanDEM-X, UAV and TLS) to quantify right-lateral and vertical offsets ranging from ∼ 1 m to ∼ 4 km over a length of 238 km. The smaller offsets document the deformation associated with the last surface-rupturing earthquake that affects several Bronze to Iron Age burial mounds. Their analysis yields a robust segmentation model comprising 6 segments of 20 to 51 km in length, a maximum co-seismic slip value of 4.8 m ± 0.5 m located near the center of the rupture. Our observations precise the varying kinematics along strike, bring new evidence of repeated faulting and confirm a Mw of 7.8 ± 0.3. [ABSTRACT FROM AUTHOR]

Numerical simulations based on continuum mechanics are promising methods for the estimation of surface fault displacements. We developed a parallel finite element method program to perform such simulations and applied the program to reproduce the 2016 Kumamoto earthquake, where surface rupture was observed. We constructed an analysis model of the 5 × 5 × 1 km domain, including primary and secondary faults, and inputted the slip distribution of the primary fault, which was obtained through inversion analysis and the elastic theory of dislocation. The simulated slips on the surface were in good agreement with the observations. We then conducted a predictive simulation by inputting the slip distributions of the primary fault, which were determined using a strong ground motion prediction method for an earthquake with a specified source fault. In this simulation, no surface slip was induced in the sub-faults. A large surface slip area must be established near a sub-fault to induce the occurrence of a slip on the surface.

A critical review is conducted of a selection of paleoseismic works published on, or close to, metropolitan France over the last 30 years. The evolution of these works may be subdivided into three periods: dawn of French paleoseismic studies (${\approx }$1990–1995), beginning of a multidisciplinary paleoseismologic approach, and paleoseismic studies in the first decades of the 21st century. This review of the most interesting paleoseismic studies at nine trench sites indicates that it is often difficult to associate Quaternary surface deformations with a well-identified fault. However, these studies also provided important results demonstrating that even in regions of low seismicity, seismic ruptures can repeat on the same low slip rate fault, thus providing evidence that historical seismicity is not sufficient to assess seismic hazard in metropolitan France. Finally, recommendations are provided for future paleoseismic investigations in low-seismicity regions.

The Koyna region in western India, characterized by recurrent seismic activity over more than five decades and confined largely within a 20 km × 30 km area and ∼10 km in depth, is a classical site to study earthquake processes. The largest earthquake in the region, the M 6.3 Koyna earthquake of December 1967, formed a ∼NNE-SSW trending surface rupture, known as Donichawadi fissure zone. The fissure zone, mapped originally over a length of ∼4 km and width of ∼200 m between Nanel and Kadoli by the Geological Survey of India (GSI) in the wake of the earthquake, comprises en-echelon fractures, near-vertical fissures, oblique or diagonal tensional cracks, mole tracks, soil lumps and laterite boulders in paddy cultivated land. We review the Donichawadi fissure zone in the light of extensive seismological data acquired in the past five decades, surface mapping studies, recent geophysical studies, soil-gas helium studies over the fissure zone during 1996–1997, chemical and noble gas isotope compositions of formation gases, and subsurface fracture data from downhole image logs in a 3 km - deep scientific borehole drilled in 2017. Integration of the datasets provide clinching evidence that the Donichawadi fissure zone is the surface manifestation of a deeper crustal fault (referred as Donichawadi fault) that has been active for more than 55 years and yield critical new insights on the geometry, distribution and possible subsurface disposition of the fissures and the associated fractures in the subsurface. We conclude that the Donichawadi fault offers a potential target for further deep probing through scientific drilling, downhole measurements and long-term monitoring to gain new insights into the genesis of triggered earthquakes in the area.

On 8 January 2022, a seismic event of significant magnitude (Mw 6.7, Ms 6.9) occurred in the northeastern region of the Tibetan Plateau. This earthquake was characterized by left-lateral strike-slip motion, accompanied by a minor reverse movement. The Menyuan earthquake resulted in the formation of two main ruptures and one secondary rupture. These ruptures were marked by a left-lateral step zone that extended over a distance of 1 km between the main ruptures. The length of the rupture zones was approximately 37 km. The surface rupture zone exhibited various features, including left-lateral offset small gullies, riverbeds, wire fences, road subgrades, mole tracks, cracks, and scarps. Through a comprehensive field investigation and precise measurement using unmanned aerial vehicle (UAV) imagery, 111 coseismic horizontal offsets were determined, with the maximum offset recorded at 2.6 ± 0.3 m. The analysis of aftershocks and the findings from the field investigation led to the conclusion that the earthquake was triggered by the Lenglongling fault and the Tuolaishan fault. These faults intersected at a release double-curved structure, commonly referred to as a stepover. During this particular process, the Lenglongling fault was responsible for initiating the coseismic rupture of the Sunan–Qilian fault. It is important to note that the stress applied to the Tuolaishan fault has not been fully relieved, indicating the presence of potential future hazards.

The Sichuan–Yunnan block is located in the eastern of Tibetan Plateau and exhibits strong tectonic and earthquake activity. The Maisu fault is an E–W-trending fault within this block. Via interpretations of remote-sensing imagery and field surveys, we identified a earthquake surface rupture zone that has developed along the Maisu fault; we then estimated its Holocene activity. The surface rupture extends westward from the town of Puma, Sichuan Province, to the village of Worilong, Xizang Province, and has a length of approximately 45 km. According to a fault outcrop and carbon-14 dating of a profile near the village of Yongqu, Xizang Province, the most recent earthquake along this rupture may have occurred after 1850 ± 30 BP. The Maisu fault extends eastward and may intersect the Garzê–Yushu fault. Accordingly, as a secondary fault, the Maisu fault likely accommodates the partitioned horizontal slip deformation of the Garzê–Yushu fault.

The 4.9 Mw earthquake of 11 November 2019 at Le Teil (France) occurred at a very shallow depth (about 1 km), inducing the surface rupture of La Rouvière fault. The question was raised shortly after about the potential impact of a nearby surface quarry. Thanks to satellite differential interferometry, here, we revealed the existence of a secondary surface rupture of the quasi-parallel Bayne Rocherenard fault. A newly processed seismic cross-section allowed us to shape the three-dimensional geometry of the local three-fault system. Assuming that the earthquake was triggered by the impact of meteoric water recharge, our numerical simulations show that the hydraulic pressure gradient at depth was at a maximum during the period of 2010–2019, just before the seismic event. The estimated overpressure at the intersection of the two faults, which is the most probable place of the hypocenter, was close to 1 MPa. This hydraulic effect is about two and a half times larger than the cumulative effect of mechanical stress release due to the mass removal from the surface quarry over the two past centuries. This work suggests a rapid hydraulic triggering mechanism on a network of faults at a shallow depth after a heavy rainfall episode.

On November 11, 2019, a M$_{\mathrm{w}}$ 4.9 earthquake hit the region close to Montelimar (lower Rhône Valley, France), on the eastern margin of the Massif Central close to the external part of the Alps. Occuring in a moderate seismicity area, this earthquake is remarkable for its very shallow focal depth (between 1 and 3 km), its magnitude, and the moderate to large damages it produced in several villages. InSAR interferograms indicated a shallow rupture about 4 km long reaching the surface and the reactivation of the ancient NE–SW La Rouvière normal fault in reverse faulting in agreement with the present-day E–W compressional tectonics. The peculiarity of this earthquake together with a poor coverage of the epicentral region by permanent seismological and geodetic stations triggered the mobilisation of the French post-seismic unit and the broad French scientific community from various institutions, with the deployment of geophysical instruments (seismological and geodesic stations), geological field surveys, and field evaluation of the intensity of the earthquake. Within 7 days after the mainshock, 47 seismological stations were deployed in the epicentral area to improve the Le Teil aftershocks locations relative to the French permanent seismological network (RESIF), monitor the temporal and spatial evolution of microearthquakes close to the fault plane and temporal evolution of the seismic response of 3 damaged historical buildings, and to study suspected site effects and their influence in the distribution of seismic damage. This seismological dataset, completed by data owned by different institutions, was integrated in a homogeneous archive and distributed through FDSN web services by the RESIF data center. This dataset, together with observations of surface rupture evidences, geologic, geodetic and satellite data, will help to unravel the causes and rupture mechanism of this earthquake, and contribute to account in seismic hazard assessment for earthquakes along the major regional Cévenne fault system in a context of present-day compressional tectonics.

Abstract The Mw7.0 2016 Kumamoto earthquake occurred on the previously mapped Futagawa–Hinagu fault causing significant strong ground motions. A ~ 30-km-long dextral surface rupture appeared on the major fault zone and dextral slip was up to 2–3 m. However, the surface ruptures were also broadly and remotely distributed approximately 10 km away from the primary rupture zone. These numerous distributed secondary surface slips with vertical displacement of less than a few tens of centimeters were detected by the interferometric synthetic aperture radar (InSAR) technology in previous studies. Such displacements occurred not only on previously mapped faults but also on unknown traces. Here, we addressed the following fundamental issues: whether the broadly distributed faults were involved in the past major earthquakes in the neighborhood, and how the fault topography of such secondary faults develops, seismically or aseismically. To find clues for understanding these issues, we show the results of field measurements of surface slips and paleoseismic trenching on distributed secondary faults called the Miyaji faults inside the Aso caldera, 10 km away from the eastern end of the primary rupture zone. Field observations revealed small but well-defined dextral slip surface ruptures that were consistent with vertical and dextral offsets derived from InSAR. On the trench walls, the penultimate event with vertical displacements almost similar to the 2016 event was identified. The timing of the penultimate event was around 2 ka, which was consistent with that of the primary fault and archeological information of the caldera. Considering the paleo-slip event and fault models of the Miyaji faults, they were presumed not to be source faults, and slip on these faults have been triggered by large earthquakes along major adjacent active faults. The results provide important insights into the seismic hazard assessment of low-slip-rate active faults and fault topography development due to triggered displacement along secondary faults.

The MS 6.9 Menyuan earthquake in Qinghai Province, west China is the largest earthquake by far in 2022. The earthquake occurs in a tectonically active region, with a background b-value of 0.87 within 100 ​km of the epicenter that we derived from the unified catalog produced by China Earthquake Networks Center since late 2008. Field surveys have revealed surface ruptures extending 22 ​km along strike, with a maximum ground displacement of 2.1 ​m. We construct a finite fault model with constraints from InSAR observations, which showed multiple fault segments during the Menyuan earthquake. The major slip asperity is confined within 10 ​km at depth, with the maximum slip of 3.5 ​m. Near real-time back-projection results of coseismic radiation indicate a northwest propagating rupture that lasted for ∼10 ​s. Intensity estimates from the back-projection results show up to a Mercalli scale of IX near the ruptured area, consistent with instrumental measurements and the observations from the field surveys. Aftershock locations (up to January 21, 2022) exhibit two segments, extending to ∼20 ​km in depth. The largest one reaches MS 5.3, locating near the eastern end of the aftershock zone. Although the location and the approximate magnitude of the mainshock had been indicated by previous studies based on paleoearthquake records and seismic gap, as well as estimated stressing rate on faults, significant surface-breaching rupture leads to severe damage of the high-speed railway system, which poses a challenge in accurately assessing earthquake hazards and risks, and thus demands further investigations of the rupture behaviors for crustal earthquakes.

In Taiwan, the main purpose of earthquake fault zone legislation is to prevent earthquake-related disasters around the surface traces of active faults, particularly in urban areas. Here, the Geologically Sensitive Area (GSA) of the Milun Fault (Milun Earthquake Fault Zone) is used as an example to reveal the importance of such legislation. Field data collected along the Milun Fault before and after the 2018 Hualien Earthquake were used to reveal the reappearance of damages within the GSA. The 2018 Hualien Earthquake represents one of the shortest recurrence intervals (67 years) among all major faults in Taiwan. Most of the surface ruptures and damaged buildings in Hualien City were within the Milun Fault GSA and concentrated on the hanging wall of the fault. Moreover, 61% (91/148) of the damaged buildings and 83% (692/835) of the surface ruptures occurred within 100 m of the fault line. The results of this study demonstrate the importance of defining GSAs of active faults for mitigating earthquake hazards. [ABSTRACT FROM AUTHOR]

The 1714 Bhutan earthquake was one of the largest in the Himalaya in the last millennium. We show that the surface rupture caused by this earthquake extended further to the east than previously known, it was at least 175 km long, with slip exceeding 11 m at our study site. The age of the surface rupture was constrained by a combination of radiocarbon and traditional optically stimulated luminescence dating of affected river sediments. Computations using empirical scaling relationships, fitting historical observations and paleoseismic data, yielded a plausible magnitude of Mw 8.1 ± 0.4 and placed the hypocentre of the 1714 Bhutan earthquake on the flat segment of the Main Himalayan Thrust (MHT), the basal décollement of the Himalayan orogen. Calculations of Coulomb stress transfer indicate that great earthquakes along the leading part of the MHT would cause surface rupture. In contrast, distal earthquakes may not immediately trigger surface rupture, although they would increase the stresses in the leading part of the MHT, facilitating future surface-rupturing earthquakes. Frontal earthquakes would also transfer stress into the modern foreland basin facilitating southward propagation of the MHT as a blind basal décollement. In conclusion, studies of surface-rupturing events alone likely underestimate the seismic slip along the Himalayan megathrust.

The probabilistic fault displacement hazard analysis method is one of the new methods in estimating the amount of possible displacement in the area at risk of causal fault rupture. In this study, using the probabilistic approach and earthquake method, the surface displacement of the North Tabriz fault has been investigated, and the probable displacement in different return periods has been estimated as contour maps. Assuming a strike-slip mechanism of the North Tabriz fault and earthquake method, to estimate the probability of displacement due to surface rupture, according to the surface ruptures caused by earthquakes of 1721 and 1780 North Tabriz fault, which were associated with 50 and 60 km of surface rupture respectively, a 50-60 km long section of North Tabriz fault was selected as the source of possible surface rupture. Due to a lack of data on large-scale earthquakes in northwestern Iran, the trace of North Tabriz fault is assumed to be a simple trace. This leads to a great epistemic uncertainty in the obtained possible displacement values Owing to the passage of the North Tabriz fault through the residential area of Tabriz and destructive historical earthquakes, it is essential to estimate the possible future displacements of this fault. According to paleoseismic studies, probabilistic displacements were considered between zero to 4.5 and zero to 7.1 m, respectively. Using the paleoseismic studies and the catalog of historical earthquakes, the return period and the probable magnitude of the North Tabriz fault are 645 years and Mw~7.7. In the case of exceedance rate of 5% in 475 and 2475 years, the maximum displacement is estimated up to a distance of 70 and 100 meters from the site. The attenuation relationships used in this study were derived from the fitting of seismic data occurred in different parts of the world. To reduce the uncertainty in this hazard analysis and the values of possible displacement, the data of surface rupture of strike-slip earthquakes in Iran can be used to fit and obtain local attenuation relationships. In this research, considering the attenuation relationship of Petersen, the estimated maximum probability displacement of the North Tabriz fault at an exceedance rate of 5% in 50 years, for 4.5 and 7.1m displacements, is 186 cm. Moreover, the estimated maximum probability displacements in 475 and 2475 years are 469 cm and 655 cm, respectively. [ABSTRACT FROM AUTHOR]

Abstract A large Mw 7.5 earthquake occurred at 18.03 on 28 September 2018 in the Donggala–Palu area of Central Sulawesi, Indonesia, which triggered a tsunami, liquefaction, and landslides. A 160-km rupture zone was formed on the surface along the NS to NNW–SSE trending Palu–Koro fault (PKF) system through three regencies: Donggala, Palu, and Sigi. Obvious surface ruptures associated with the earthquake were not observed in the epicentral area. Surface ruptures with a small displacement of both sinistral and westerly downward slip components appear south of the epicentral area in the Donggala area. The event induced widespread subsidence of the Donggala coastal area on the west side of the rupture zone. Passing across the Palu bay, the rupture cuts through the urban area of Palu city and extends across alluvial fans along the western side of the Palu basin showing large displacements with a predominant sinistral slip up to 4.2 m and subordinate easterly downward slip components. Approximately 5 m of anomalously high vertical displacement with 3 m of horizontal displacement occurs in an extensional bend in the southern area of the Palu basin. In the Sigi valley, the rupture zone follows the previously known PKF trace showing predominant sinistral and subordinate easterly downward slip, of which displacement is 0.9 m sinistral and 0.5 m easterly downward at the site 60 km south of Palu city and gradually smaller toward the south. These distributions of rupture zones and displacements suggest that rupture of the 2018 earthquake unilaterally propagated southwards and resulted in the movement of the eastern side of the fault towards the NNW.

Abstract The 2011 Tohoku-Oki offshore subduction earthquake (M w 9.0) triggered many normal-type earthquakes inland in northeastern Japan. Among these were two very similar normal-faulting earthquakes in 2011 (M w 5.8) and 2016 (M w 5.9), which created surface ruptures along the newly named Mochiyama fault within the southern Abukuma Mountains, northeastern Japan, where no active faults had been previously mapped by interpretation of aerial photographs. We conducted field surveys in this area immediately after both earthquakes, and we performed trench excavations and observations of fault fracture zones after the 2016 event. These activities were complemented by an interferometric synthetic aperture radar analysis that mapped the areas of deformation and locations of surface discontinuities for both events. The combined results document the coseismic behavior of the Mochiyama fault during both events. Subtle tectonic geomorphic features associated with the fault were evident in a lidar digital elevation model of the area, and layered structures of gouge were documented in the field. These lines of evidence indicate repeated activity at shallow crustal levels and the possibility of Quaternary activity. In addition, our trench excavations revealed at least one faulting event before 2011. Our comparison of paleoseismic records on this and two other normal faults in the Abukuma Mountains suggests that great earthquakes in the Japan Trench supercycle of 500–700 years do not consistently trigger ruptures on these faults, and the case of 2011, in which the Tohoku-Oki megathrust earthquake triggered all three faults, is a rare occurrence.

The Eastern European Alps are characterized by slow active deformation with low- to moderate seismicity. Recurrence rates of severe earthquakes exceed the time span of historical documentation. Therefore, historical and instrumental earthquake records might be insufficient for seismic hazard assessment and high-quality paleoseismic data is required. However, primary geological observations of postglacial fault activity are scarcely found, because major faults are buried below thick sedimentary sequences in glacially overdeepened valleys. Moreover, high erosion rates, gravitational slope processes and penetrative anthropogenic landscape modification often obscure geomorphic features related to surface ruptures. Here we present one of the rare paleoseismic data sets showing both on-fault evidence as subaqueous surface ruptures and off-fault evidence as multiple coeval mass-transport deposits (MTDs) and megaturbidites within a single high-resolution seismic-stratigraphic framework of the inner-alpine lake Achensee. Co-occurrence of on-fault and off-fault paleoseismic evidence on three stratigraphic levels indicates seismic activity with inferred moment magnitudes MW ∼6–6.5 of the local, lake-crossing Sulzgraben-Eben thrust at ∼8.3 ka BP and twice in Late Glacial times. Additional eight stratigraphic levels with only off-fault paleoseismic evidence document severe seismic shaking related to the historical MW ∼5.7 earthquake in Hall (CE 1670) and seven Holocene earthquakes, which have exceeded a local seismic intensity of ∼VI (EMS-98) at Achensee. Furthermore, we discuss natural and methodological influencing factors and potential pitfalls for the elaboration of a subaqueous paleoseismic record based on surface ruptures and multiple, coeval MTDs.

The Hexi Corridor is located beyond the northeastern edge of the Tibetan Plateau, and it is bounded by a series of active thrusts along the northern margin of the Qilian Shan and the southern piedmont of the Longshou Shan. Historically, five destructive earthquakes have occurred along the Hexi Corridor, which indicates that this region poses high potential seismic risks. The 1609 Hongyapu earthquake occurred along the Fodongmiao-Hongyazi fault in the northern Qilian Shan, China, and it killed more than 840 people and destroyed a large number of buildings. Presently, there are different opinions as to the distribution and length of the surface rupture of this event along the Fudongmiao–Hongyazi fault. Thus, we searched all of the fault scarps on the Holocene surfaces and suspected surface rupture locations related to the 1609 earthquake based on previous studies and developed detailed remote-sensing interpretations along the fault. An abundance of north-facing scarps on the younger fans and terrace faces, slightly higher than the active modern stream bed, were found along the Fodongmiao-Hongyazi fault in the area ranging from the Hongshuiba River (39.52°N, 98.41°E) in the west to the Shuiguan River (39.07°N, 99.37°E) in the east. Based on our research, we estimate a surface rupture length as ∼98 km based on the distribution of the fault scarps on Late Holocene surfaces and constraints provided by age dating. Most of the surface ruptures are preserved as fault scarps and indicate an average vertical surface offset of ∼1.0 m, a value found consistently in three segments of the fault. The surface rupture features indicate that segments of the fault ruptured together coseismically during the 1609 earthquake, i.e., a multisegment rupture. Using the surface fault traces, length of 98 or 90 km (without the Shuiguan River section), dip of 30° inferred from previous reflection profiles, a rigidity of 3.3 × 1010 N/m2, and dip slip average as 1.9 m converted from our observations of the offsets, we computed the magnitude of this event as ca. Mw 7.2–Mw 7.4.

Abstract A fundamental topic in earthquake studies is understanding the extent to which fault rupture at the surface is localized on primary fault strands as opposed to distributed tens to hundreds of meters away from primary ruptures through off‐fault deformation (OFD) via a combination of discrete secondary faulting and bulk deformation. The 2019 Ridgecrest, CA Mw6.4 and Mw7.1 earthquakes provide an opportunity to explore this problem via comparison of published field‐based and mostly on‐fault offset measurements, with new lateral displacement measurements made over length scales of hundreds of meters across the primary rupture using WorldView satellite images collected before and after the earthquakes. A mean fit to the field observations underestimates net slip (pixel‐correlation results) by an average of 0.4 m along the Mw6.4 rupture (∼41% of net left‐lateral displacement) and 0.7 m along the Mw7.1 rupture (∼65% of net right‐lateral displacement). We attribute these differences to substantial OFD along the lengths of the Mw6.4 (∼59%) and Mw7.1 (∼35%) ruptures. A maximum fit to the field observations provides an improved match to the pixel correlation results (difference of 0.1–0.2 m or ∼76%–98% of net displacement). OFD may in part depend on displacement magnitude, where locations along the rupture with smaller displacements (

A critical review is conducted of a selection of paleoseismic works published on, or close to, metropolitan France over the last 30 years. The evolution of these works may be subdivided into three periods: dawn of French paleoseismic studies (≈1990–1995), beginning of a multidisciplinary paleoseismologic approach, and paleoseismic studies in the first decades of the 21st century. This review of the most interesting paleoseismic studies at nine trench sites indicates that it is often difficult to associate Quaternary surface deformations with a well-identified fault. However, these studies also provided important results demonstrating that even in regions of low seismicity, seismic ruptures can repeat on the same low slip rate fault, thus providing evidence that historical seismicity is not sufficient to assess seismic hazard in metropolitan France. Finally, recommendations are provided for future paleoseismic investigations in low-seismicity regions. [ABSTRACT FROM AUTHOR]

Abstract Large earthquakes occurred in the central part of Kumamoto Prefecture on April 14–16, 2016, causing severe damage to the northern segment of the Hinagu faults and the eastern segment of the Futagawa faults. Earthquake surface ruptures appeared along these faults and on the Aso volcanic edifice, which in turn generated landslides. We conducted landform change analysis of the central cones of Aso volcano by using satellite and aerial photographs. First, we categorized the topographical changes as surface scarps, arc-shaped cracks, and linear cracks. Field survey indicated that landslides caused the scarps and arc-shaped cracks, whereas faulting caused the linear cracks. We discovered a surface rupture concentration zone (RCZ) formed three ruptures bands with many surface ruptures and landslides extending from the west foot to the center of the Aso volcanic edifice. The magmatic volcanic vents that formed during the past 10,000 years are located along the north margin of the RCZ. Moreover, the distribution and dip of the core of rupture concentration zone correspond with the Nakadake craters. We conclude that a strong relationship exists between the volcanic vents and fault structures in the central cones of Aso volcano. Graphical abstract .

A large Mw 7.5 earthquake occurred at 18.03 on 28 September 2018 in the Donggala–Palu area of Central Sulawesi, Indonesia, which triggered a tsunami, liquefaction, and landslides. A 160-km rupture zone was formed on the surface along the NS to NNW–SSE trending Palu–Koro fault (PKF) system through three regencies: Donggala, Palu, and Sigi. Obvious surface ruptures associated with the earthquake were not observed in the epicentral area. Surface ruptures with a small displacement of both sinistral and westerly downward slip components appear south of the epicentral area in the Donggala area. The event induced widespread subsidence of the Donggala coastal area on the west side of the rupture zone. Passing across the Palu bay, the rupture cuts through the urban area of Palu city and extends across alluvial fans along the western side of the Palu basin showing large displacements with a predominant sinistral slip up to 4.2 m and subordinate easterly downward slip components. Approximately 5 m of anomalously high vertical displacement with 3 m of horizontal displacement occurs in an extensional bend in the southern area of the Palu basin. In the Sigi valley, the rupture zone follows the previously known PKF trace showing predominant sinistral and subordinate easterly downward slip, of which displacement is 0.9 m sinistral and 0.5 m easterly downward at the site 60 km south of Palu city and gradually smaller toward the south. These distributions of rupture zones and displacements suggest that rupture of the 2018 earthquake unilaterally propagated southwards and resulted in the movement of the eastern side of the fault towards the NNW. [ABSTRACT FROM AUTHOR]

DOI:10.17014/ijog.3.2.95-105An assessment of surface rupture and collateral ground failures can help to evaluate the impact of future earthquakes. This paper presents the results of a field survey conducted to map the surface rupture and geotechnical phenomena associated with the ground shaking during the July 2, 2013 earthquakes in Tanah Gayo Highland. The objectives of this survey are to document and to characterize the surface ruptures as well as to identify types of earthquake-induced ground failures. Results of the survey identified four best sites of possible surface rupture. Two locations are obvious surface ruptures that can be traced on primary topographic feature of the active fault segment from the north to the south, crossing Pantan Terong Hill. The fault segment has a total mapped length of 19 km, with WNW trending zone and a dextral rupture offset. The ground shaking also resulted in landslides and liquefaction in areas underlain by very fine-grained tuffaceous sands. Based on the field survey, it can be concluded that the newly defined active fault segment, the Pantan Terong segment, is likely the segment that ruptured at the July 2, 2013 Tanah Gayo earthquake. Due to the soil types and unstable rocky slopes in the hilly Central Aceh region, large-scale landslides are primary risks during an earthquake event in this region.

Abstract: The detailed features of an earthquake surface rupture may decay quickly in the landscape due to erosion or repair, such that primary displacements are seldom available for repeated study within the weeks following an earthquake. Here we describe a rapidly deployable field workflow using structure‐from‐motion (SfM) photogrammetry to produce three‐dimensional models of offset features and apply the technique to the 24 August 2014 Mw 6.0 South Napa earthquake surface rupture. We use repeated analyses of SfM point clouds using 3‐D interactive virtual reality tools to derive precise and reproducible fault‐slip measurements along the surface rupture and document the temporal evolution of afterslip at two sites along its trace. The SfM technique, combined with 3‐D virtual reality, enables archiving of primary field relationships and assessment of uncertainty in those data to a degree that was previously inaccessible. [ABSTRACT FROM AUTHOR]

We digitize surface rupture maps and compile observational data from 67 publications on ten of eleven historical, surface-rupturing earthquakes in Australia in order to analyze the prevailing characteristics of surface ruptures and other environmental effects in this crystalline basement-dominated intraplate environment. The studied earthquakes occurred between 1968 and 2018, and range in moment magnitude (Mw) from 4.7 to 6.6. All earthquakes involved co-seismic reverse faulting (with varying amounts of strike-slip) on single or multiple (1−6) discrete faults of ≥ 1 km length that are distinguished by orientation and kinematic criteria. Nine of ten earthquakes have surface-rupturing fault orientations that align with prevailing linear anomalies in geophysical (gravity and magnetic) data and bedrock structure (foliations and/or quartz veins and/or intrusive boundaries and/or pre-existing faults), indicating strong control of inherited crustal structure on contemporary faulting. Rupture kinematics are consistent with horizontal shortening driven by regional trajectories of horizontal compressive stress. The lack of precision in seismological data prohibits the assessment of whether surface ruptures project to hypocentral locations via contiguous, planar principal slip zones or whether rupture segmentation occurs between seismogenic depths and the surface. Rupture centroids of 1−4 km in depth indicate predominantly shallow seismic moment release. No studied earthquakes have unambiguous geological evidence for preceding surface-rupturing earthquakes on the same faults and five earthquakes contain evidence of absence of preceding ruptures since the late Pleistocene, collectively highlighting the challenge of using mapped active faults to predict future seismic hazards. Estimated maximum fault slip rates are 0.2−9.1 m Myr−1 with at least one order of uncertainty. New estimates for rupture length, fault dip, and coseismic net slip can be used to improve future iterations of earthquake magnitude—source size—displacement scaling equations. Observed environmental effects include primary surface rupture, secondary fracture/cracks, fissures, rock falls, ground-water anomalies, vegetation damage, sand-blows/liquefaction, displaced rock fragments, and holes from collapsible soil failure, at maximum estimated epicentral distances ranging from 0 to ~250 km. ESI-07 intensity-scale estimates range by ± 3 classes in each earthquake, depending on the effect considered. Comparing Mw-ESI relationships across geologically diverse environments is a fruitful avenue for future research.

Large pre-historical earthquakes leave traces in the geological and geomorphological record, such as primary and secondary surface ruptures and mass movements, which are the only means to estimate their magnitudes. These environmental earthquake effects (EEEs) can be calibrated using recent seismic events and the Environmental Seismic Intensity Scale (ESI2007). We apply the ESI2007 scale to the 1992 MS7.3 Suusamyr Earthquake in the Kyrgyz Tien Shan, because similar studies are sparse in that area and geological setting, and because this earthquake was very peculiar in its primary surface rupture pattern. We analyze literature data on primary and secondary earthquake effects and add our own observations from fieldwork. We show that the ESI2007 distribution differs somewhat from traditional intensity assessments (MSK (Medvedev-Sponheuer-Karnik) and MM (Modified Mercalli)), because of the sparse population in the epicentral area and the spatial distribution of primary and secondary EEEs. However, the ESI2007 scale captures a similar overall pattern of the intensity distribution. We then explore how uncertainties in the identification of primary surface ruptures influence the results of the ESI2007 assignment. Our results highlight the applicability of the ESI2007 scale, even in earthquakes with complex and unusual primary surface rupture patterns.