Coseismic Surface Rupture Research Articles

Coseismic surface ruptures of 20 strike-slip earthquakes measured from geodetic imaging data

Observations of coseismic surface ruptures are widely used for examining faulting mechanics and kinematics, and in fault displacement hazard analysis. Here, first, we provide new remote sensing observations of 20 historic surface rupturing continental strike-slip earthquakes (6.1 ≤ Mw≤ 7.9). To measure the near-field surface deformation pattern, we have processed a range of raw radar and optical images from satellite and aerial platforms with pixel tracking techniques, and in two cases using standard interferometric synthetic aperture radar (InSAR). We provide a range of observations, including surface displacement maps that constrain at least the horizontal component of surface motion (2D), and for three events the full 3D components. Second, we provide strain invariants for each event, which includes the finite dilatational strain, strain magnitudes, the vorticity, and maximum shear strain. Third, we provide a total of 134 surface fault rupture traces that are mapped manually from the displacement maps. Finally, we provide 2648 measurements of coseismic horizontal fault-parallel surface fault slip that are measured objectively using swath profiles with a function fitting method that we have developed.

Surface ruptures of the 2022 Guanshan-Chihshang earthquakes in central Longitudinal Valley area, eastern Taiwan

AbstractThe 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.

Timing and characteristics of co-seismic surface ruptures in the Yadong rift, southern Tibet

The Yadong-Gulu rift (YGR) is the most prominent and seismically active of the seven main ∼ NS-trending rifts in southern Tibet. Although the morphology of the southern YGR clearly indicates it has witnessed large earthquakes in the past, and despite its significant late Quaternary throw rates of ∼1 mm/yr, no large historical or instrumental earthquakes have been reported, including in the southernmost Pagri half-graben, in contrast to the northern part of the rift which is highly seismically active. Here, geomorphic characteristics helped us constrain the timing of a paleoearthquake that produced surface ruptures along the Pagri half-graben, used to document its past activity and evaluate its seismic hazard. We demonstrate that the co-seismic surface ruptures extend for ∼65 km along the Yadong normal fault, with a maximum vertical displacement ranging from 2 to 4.0 ± 0.1 m. Based on empirical relationships between magnitude, surface rupture length, and fault displacement, we suggest that this event may correspond to a Mw6.9–7.2 earthquake. Combined with previous studies, our radiocarbon (14C) and Optically Stimulated Luminescence (OSL) ages from three pits within the earthquake wedge across the surface ruptures constrain the paleoearthquake timing at 3470-2056 years BP. We suggest that the southern YGR currently has a high regional seismic hazard for a Mw6.8–7.1 earthquake, considering the significant throw rates and long timespan since the last strong event. Furthermore, we suggest that such different seismic activity and throw/extension rates between the southern and northern YGR may be explained by different upper crustal rheology behavior and mid-crustal structure.

Kinematic and dynamic fault slip analyses: Implications from the surface rupture of the 2023 Elbistan (Kahramanmaraş) (Mw7.6) earthquake, Türkiye

On 6 February 2023, the Elbistan (Kahramanmaraş) (Mw7.6) earthquake produced a strike-slip type coseismic surface rupture zone, involving the sinistral slip of the Doğanşehir Fault (DF) and Çardak Fault (ÇF). Fault slickenlines and seismic slickenlines were included in the inversion as part of the dynamic analysis. The inversion of fault slickenlines collected from nine outcrops along the surface rupture following the earthquake, many of which developed during the event and are referred to as coseismic slickenlines, reveals a strike-slip stress regime (σ2 = σv) characterized by a NE-SW (mean azimuth: N045°E) σ1 (maximum) axis. Relict slip planes adjacent to main slip surfaces were found to host slickenlines that appear much older than the most recent earthquake, referred to as paleoslip slickenlines. Inversion of the paleoslip slickenline collected from four outcrops reveals an extensional stress regime (σ1 = σv) characterized by a NE-SW σ3 (min) axis, consistent with previously published studies. To define a significant stress tensor concerning present-day faulting within the investigated area, the inversion method was applied to the seismic slickenlines of shallow earthquakes in the surface rupture area. The inversion of sixty selected nodal planes reveals a strike-slip stress regime (σ2 = σv) characterized by an NNE–SSW (N10°E) σ1 (max) axis. Besides, the moment tensor summation analysis using displacement vectors inferred from visible field markers offset during the earthquake was applied to the seismic slickenlines as part of the kinematic analysis. The shortening and extension results for the moment tensor summation are 044/36 and 307/11 indicating NE-SW compression. Results of the moment tensor summation (weighted by fault displacement) agree broadly with the inversion of seismic slickenlines results, indicating an NE orientation for shortening and an SE orientation for extension.

Late Quaternary right-lateral slip rate along the Tangyuan segment of the Yilan–Yitong Fault Zone on the NE China Plain

The slip rate of strike-slip active faults is crucial for fault rupture behavior analysis and seismic hazard assessment. Although many segments of the Yilan–Yitong Fault Zone (YYFZ) in NE China have been strongly deformed since the late Quaternary, little progress has been made on its slip rate. With the help of high-resolution satellite images, detailed field investigations, seismic reflections, and Quaternary chronological dating, we mainly studied the late Quaternary right-slip rate of the YYFZ. Field investigations revealed an ∼15 km long by ∼1–2 m high-surface scarp belt extending along the Tangyuan graben interior, with a series of sag ponds and small parallel bulges. Research has revealed that the most recent paleoearthquake (∼M 7.0) occurred between 2,800± 600 a BP and 1,700 ± 200 a BP, with evidence of coseismic surface rupture. The T2 terrace abandonment age of the Heijin River is approximately 55.13 ± 1.78 ka (OSL), and the maximum cumulative right-lateral offset may reach 110 ± 5 m. Thus, the maximum right-slip rate of the Tangyuan segment of the YYFZ since the late Quaternary is constrained to 1–2 mm/a according to the upper terrace model. This study suggests that the presence of a new fault in the basin interior merits more attention when assessing the influential surface range and earthquake potential along the YYFZ, and the features of “low tectonic loading rate, activity migration in space, and clustering in time separated by ten thousand years of seismic quiescence” observed along the YYFZ are highly important for earthquake model construction and tectonic deformation studies in stable continental regions (SCRs).

Multiple Fold Earthquakes Recorded by the Paleoseismic Surface Ruptures of Bending-Moment Faults in the Qiulitage Anticline, South Tianshan, China

Abstract Bending-moment faults (BMFs), as a fundamental type of secondary faulting, are intrinsically linked to the primary causative faults within active thrust-fold belts. When these faults thrust through the ground surface, the resulting geomorphic scarps offer the characteristics of local earthquake recurrence. This information helps to fill a gap left by main faults, which often lack coseismic surface ruptures. The Qiulitage anticline where the 1949 M 7¼ Kuqa earthquake occurred is an active thrust-and-fold belt predominantly governed by blind faults. In addition, several typical BMFs extensively crop out as surface scarps in the front of the mountain. Our research concentrates on the well-developed BMF scarps in this region and seeks to explore the recurrence characteristics of paleoearthquakes, which remain inadequately comprehended. Our study reveals that (1) secondary BMF with high enough magnitude can directly generate coseismic ground ruptures, and (2) the seismic behavior of BMFs exhibits a degree of repeatability, potentially linked to the concurrent movement of various BMFs or the solitary action of a single fault. However, the case study presented in this article also highlights the limitation of fold earthquake research because of the swift attenuation of coseismic fault slip as it approaches the ground surface.

High-resolution co-seismic fault offsets of the 2023 Türkiye earthquake ruptures using satellite imagery

On February 6, 2023, southern Türkiye was struck by two large earthquakes at 01:17 UTC (Mw=7.8, Pazarcık, Kahramanmaraş) and 10:30 UTC (Mw = 7.6, Elbistan, Kahramanmaraş), causing severe damage at the complex junction of the Dead Sea Fault (DSF), the Cyprus Arc and the East Anatolian Fault Zone (EAFZ). The ruptures propagated along several known strands of the southwestern termination of the EAFZ, the main Pazarcık and Karasu valley faults, and the Çardak-Sürgü fault. Here we present the high-resolution mapping of the entire coseismic surface rupture and an estimate of the rupture width, total and on-fault offset, and diffuse deformation obtained a few days to three months after the two mainshocks. The mapping is derived from image correlation of Sentinel-2 optical satellite imagery and validated with offset measurements collected on the ground. We find that the ruptures extend over lengths of 310 km and 140 km for the Mw 7.8 and Mw 7.6 mainshocks, respectively. The maximum offsets reach 7.5 ± 0.8 m and 8.7 ± 0.8 m near the epicenters of the Mw 7.8 and Mw 7.6 events, respectively. We propose a segmentation of the two ruptures based on these observations, and further discuss the location of the potential supershear rupture. The use of optical image correlation, complemented by field investigations along earthquake faults, provides new insights into seismic hazard assessment.

Investigating the structure under the Pingting Terrace from the co-seismic surface rupture of the 2022 Guanshan earthquake

AbstractOn September 17th and 18th, 2022, shallow earthquakes with magnitudes of 6.6 (ML) and 6.8 (ML) occurred in the eastern Taiwan Longitudinal Valley, which marks the collision zone between the Philippine Sea plate and the Eurasian plate, and led to noticeable surface deformation and ruptures within 70 km. This study primarily focuses on the southernmost section of the rupture zone—the Pingting Terrace. Surface rupture locations and behaviors correspond to changes in topography, providing mutual confirmation that the deformation behavior of Pingting Terrace is complex. Based on the distribution of surface ruptures and topography changes, this study roughly divides the Pingting Terrace into northern and southern segments, using the central concave feature as a boundary. The Riedel shear model analysis results show that the principal shear directions in the northern and southern segments are N–S trending and azimuth 20°, respectively. The maximum principal stress orientations are around 135° for the northern and 155° for the southern segments. These findings align with the fault mechanical investigation of the Lichi Mélange in the northern Muken River area of the Pingting Terrace. This suggests spatial changes in shear zone orientations within the Lichi Mélange, which contribute to developing pressure ridges due to transpressional forces. As a result, the Pingting Terrace experiences rapid uplift, causing the Luliao River to migrate southward into the Beinan River, while the eastern Beinan River turns to the eastward edge of the Pingting Terrace.

InSAR coseismic deformation field and seismogenic structure of the 2020 Mw6.0 Jiashi earthquake and the implication for the moderate-magnitude seismicity in the southwestern Tian Shan, western China

The Kepingtage fold-and-thrust belt in the southwestern Tian Shan in western China hosted the 2020 Mw 6.0 Jiashi earthquake with no apparent surface ruptures. The thrust nappe structure in this region is characterized by moderate-magnitude (Mw5.5-6.5) seismicity, but the seismogenic mechanisms and controlling factors remain under investigation. In this study, we utilized Sentinel-1A synthetic aperture radar satellite data to reconstruct the InSAR coseismic deformation field of the 2020 Jiashi earthquake. To address the limitation imposed by residual orbital phases during the interferometric measurement, we proposed a novel automatic method that combines ascending and descending track data with terrain features for orbit refinement. Eight comparative tests were conducted to prove the effectiveness of the proposed method. Subsequently, we inverted the jointly constrained deformation field after orbit correction to obtain the fault geometric parameters and slip distribution. Our results show that the 2020 Jiashi earthquake is characterized by right-lateral transpressive motion. The smooth interference fringes demonstrate spatially continuous surface uplift and subsidence without detectable coseismic surface ruptures, with a maximum uplift of ∼0.08 m and a maximum subsidence of ∼0.03 m, caused by the subsurface folding due to deep seismic rupture. This event is best fitted by a north-dipping fault plane with a depth of 4.2 km, a dip angle of 11.6°, and a strike of 276° beneath the Keping thrust fault. In terms of various geometric parameters of the fault, the inversion results of this study are generally similar to the focal mechanism solution provided by USGS (MWb), but are different from the focal mechanism solutions of other institutions and previous research results. Combined with the published geological investigations and seismic reflection surveys, we suggest that the seismogenic structure of the 2020 Jiashi earthquake is the lower ramp of the Keping thrust fault and the abrupt fault bend between the lower and upper ramp may limit the propagation of the coseismic rupture to the surface. The limited rupture of this event is dominated by the irregularities in fault geometry along strike and dip, as well as the lower rock strength of the cover above the detachment, which contribute to a deeper understanding of the seismic behavior in fold-and-thrust belts and the moderate-magnitude seismicity in the southwestern Tian Shan region.

Earthquake Environmental Effects and Building Properties Controlling Damage Caused by the 6 February 2023 Earthquakes in East Anatolia

On 6 February 2023, East Anatolia was devastated by two major earthquakes resulting in hundreds of thousands of collapses and tens of thousands of human casualties. This paper investigates the factors related to building properties and earthquake environmental effects (EEEs) that contributed to the building damage grade and distribution in southeastern Turkey. In regards to the building construction properties, the loose enforcement of the building code, the random urban planning solutions and the poor construction standards are the main construction deficiencies that led to one of the largest disasters in Turkey’s recent history. Regarding geological factors, the triggering of primary and secondary EEEs largely shaped the grade and distribution of damage. Where coseismic surface ruptures intersected with the built environment, heavy to very heavy structural damage was observed. This was evident in many cases along the ruptured segments of the East Anatolian Fault Zone (EAFZ). Liquefaction observed close to waterbodies caused damage typical of building foundation load-bearing capacity loss. The earthquake-triggered landslides affected mainly mountainous and semi-mountainous settlements characterized with pre-earthquake high related susceptibility. The high susceptibility to generation of EEEs was extensively confirmed in many cases resulting in extensive damage. The provided information highlights the importance of such studies for hazard mitigation and disaster risk reduction.

Strain Threshold for the Formation of Coseismic Surface Rupture

AbstractThe 2021 Mw 7.4 Maduo earthquake (eastern Tibetan Plateau), with a surface deformation zone that is characterized by multiple distinct surface rupture segments separated by segments with no surface ruptures, provides an excellent opportunity to constrain the strain threshold (minimum strain) for the formation of surface ruptures. Through sub‐pixel correlation of pre‐ and post‐event SPOT‐6/7 satellite images (pixel = 1.5 m), we derive surface displacement and shear‐strain fields of the Maduo earthquake. By quantifying the minimum shear strain along the surface rupture segments and the maximum shear strain along the segments with no surface ruptures, we estimate a rupture strain threshold, which ranges from 0.8% to 1.8% and appears to decrease with structural maturity of the causative fault. This threshold is generally consistent with a rupture strain limit (0.5%–1.5%) of intact rocks from laboratory measurements, and is higher than a commonly‐assumed strain threshold (0.5%) for inelastic deformation.

Fault geometry and low frictional control of the near-field postseismic deformation of the 2021 Mw 7.3 Maduo earthquake

The 2021 Maduo earthquake caused ∼160 km-long complex coseismic surface rupture and postseismic deformation. However, the afterslip pattern and primary reason for the overlapped coseismic slip and afterslip in shallow portion in Maduo earthquake are still unclear. Here, we used ∼0.85 yr Sentinel-1 data to obtain the time-dependent postseismic deformation of the 2021 Mw 7.3 Maduo earthquake and inverted afterslip distribution. We calculated the frictional parameter of the seismogenic fault based on the time series afterslip and depicted the rupture surface based on three-dimensional coseismic displacement. Our findings indicated that the more considerable postseismic deformation in the near-field was concentrated on the bending region near the epicenter. The maximum afterslip was ∼0.35 m in the shallow upper crust. The shallow afterslip overlapped with the coseismic rupture, mainly caused by the low frictional parameter (a – b = 0.002) and shear heating in the shallow region. The fault geometry was gentle in the supershear rupture area, while changed substantially in the west of the epicenter. This highlights that the fault bending could have controlled both coseismic and postseismic deformation pattern in near-field. It also indicates that fault bending controls the stress propagation for large strike-slip fault, which provides a new perspective for seismic risk assessment of other strike-slip faults in the Bayan Har block.

Geologic and Geophysical Evidence of Repeated Normal Faulting on the Itozawa Fault—the Source of the Mw 6.6 Iwaki Earthquake Triggered by the Mw 9.0 Tohoku-Oki Megathrust Earthquake, Northeast Japan

ABSTRACT The 2011 Mw 9.0 Tohoku-Oki earthquake ruptured the 500 km long and 200 km wide convergent plate margin between the North American and Pacific plates, and changed the crustal stress field and triggered widespread seismic activity in northeast Japan. In particular, many crustal earthquakes struck the southern Fukushima area. The largest inland normal-faulting earthquake with Mw 6.6 occurred on the northwest-trending Yunodake fault and the north-northwest-trending Itozawa fault on 11 April 2011. The coseismic surface ruptures appeared along the previously identified active and presumed active faults. To investigate the near-surface structure of the Itozawa fault, we conducted ground-penetrating radar (GPR) profiling across the fault, and two drilling surveys on its hanging-wall and footwall blocks. The GPR survey line about 50 m long was located near the previous trenching site. The GPR two-way travel-time sections were collected by common-offset modes by 50 and 100 MHz GPR systems. We acquired common midpoint ensembles on both sides of the surface rupture for depth conversion of the time sections. The resulting GPR sections show detailed subsurface structures to a depth of about 7 m. We identified event horizons for the 2011, penultimate, antepenultimate, and preantepenultimate earthquakes, indicating that the Itozawa fault has ruptured repeatedly as a normal fault. The vertical displacements during these earthquake events, obtained from the GPR sections, were about 0.8, 0.3, 0.4, and 0.7 m, respectively. These observations suggest that the coseismic surface offset amount on the Itozawa fault varies greatly. The recurrence intervals of surface-rupturing earthquakes on the Itozawa fault, calculated from the previous research and this study, are much longer than those of giant interplate earthquakes along the Japan trench, such as the 2011 Tohoku-Oki earthquake. We conclude that not every giant earthquake along the Japan trench triggers a rupture of the Itozawa fault.

Buried Alive: Imaging the 9 November 2022, Mw 5.5 Earthquake Source on the Offshore Adriatic Blind Thrust Front of the Northern Apennines (Italy)

AbstractThe prompt identification of faults responsible for moderate‐to‐large earthquakes is fundamental for understanding the likelihood of further, potentially damaging events. This is increasingly challenging when the activated fault is an offshore buried thrust, where neither coseismic surface ruptures nor GPS/InSAR deformation data are available after an earthquake. We show that on 9 November 2022, an Mw 5.5 earthquake offshore Pesaro ruptured a portion of the buried Northern Apennines thrust front (the Cornelia thrust system [CTS]). By post‐processing and interpreting the seismic reflection profiles crossing this thrust system, we determined that the activated fault (CTS) is an arcuate 30‐km‐long, NW‐SE striking, SW dipping thrust and that older structures at its footwall possibly influenced its position and geometry. The activation of adjacent segments of the thrust system is a plausible scenario that deserves to be further investigated to understand the full earthquake potential of this offshore seismogenic source.

Preliminary report of coseismic surface rupture (part) of Türkiye's MW7.8 earthquake by remote sensing interpretation

Both MW 7.8 and MW 7.5 earthquakes occurred in southeastern Türkiye on February 6, 2023, resulting in numerous buildings collapsing and serious casualties. Understanding the distribution of coseismic surface ruptures and secondary disasters surrounding the epicentral area is important for post-earthquake emergency and disaster assessments. High-resolution Maxar and GF-2 satellite data were used after the events to extract the location of the rupture surrounding the first epicentral area. The results show that the length of the interpreted surface rupture zone (part of) is approximately 75 ​km, with a coseismic sinistral dislocation of 2–3 ​m near the epicenter; however, this reduced to zero at the tip of the southwest section of the East Anatolia Fault Zone. Moreover, dense soil liquefaction pits were triggered along the rupture trace. These events are in the western region of the Eurasian Seismic Belt and result from the subduction and collision of the Arabian and African Plates toward the Eurasian Plate. The western region of Chinese mainland and its adjacent areas are in the eastern section of the Eurasian Seismic Belt, where seismic activity is controlled by the collision of the Indian and Eurasian Plates. Both China and Türkiye have independent tectonic histories.

EASRAPP: An Open-Source Semiautomatic Python GUI-Based Application for Extraction and Analysis of Surface Ruptures in a Large Earthquake

Abstract Earthquake surface ruptures record the kinematics of the rupture behavior and rheology of the fault zone. General methods of acquiring coseismic surface ruptures, including the field geological survey and the visual interpretation of remote sensing images, are generally time consuming and challenging to obtain detailed features of surface ruptures. Here, we developed an open-source semiautomatic Python graphical user interface-based application named EASRAPP (An Application for Extraction and Analysis of Surface Ruptures). EASRAPP is a graphical Python application that provides an interactive, user-friendly framework for semiautomatically extracting and analyzing earthquake surface ruptures and associated quantitative parameters. It consists of four main modules for obtaining the region of interest for surface ruptures in a remote sensing image, extracting surface ruptures, editing the vector extraction results, and analyzing the width of the surface rupture zone and strikes of all surface ruptures. Moreover, some additional functions are available, including data structure conversion for vector and raster data, vector merging, raster mosaicing, and batch cropping from multiple large images to many small images. EASRAPP is written in Python 3, based on several open-source Python packages such as Tkinter, SciPy, and so forth. Because of its modular design, it is convenient to modify the code and add new functionalities to a collaborative development environment. Furthermore, the output of the editing module may serve as a machine learning or deep learning training dataset, and offer conditions for detailed kinematic analysis and acquiring accurate width of the active fault deformation zone. EASRAPP was tested on a single unmanned aerial vehicle image to demonstrate all modules and tools. In addition, EASRAPP was also applied to other drone and satellite images to extract surface ruptures from recent and historical earthquakes. Our results indicate that: (1) the tool can quickly extract the fine structures of surface fractures, (2) EASRAPP can be used to extract surface ruptures generated by historical events, and (3) it can be applied to high-resolution aerial and satellite images.

Mapping of Soil Liquefaction Associated with the 2021 Mw 7.4 Maduo (Madoi) Earthquake Based on the UAV Photogrammetry Technology

The 2021 Mw 7.4 Maduo (Madoi) earthquake that struck the northern Tibetan Plateau resulted in widespread coseismic deformation features, such as surface ruptures and soil liquefaction. By utilizing the unmanned aerial vehicle (UAV) photogrammetry technology, we accurately recognize and map 39,286 liquefaction sites within a 1.5 km wide zone along the coseismic surface rupture. We then systematically analyze the coseismic liquefaction distribution characteristics and the possible influencing factors. The coseismic liquefaction density remains on a higher level within 250 m from the surface rupture and decreases in a power law with the increasing distance. The amplification of the seismic waves in the vicinity of the rupture zone enhances the liquefaction effects near it. More than 90% of coseismic liquefaction occurs in the peak ground acceleration (PGA) > 0.50 g, and the liquefaction density is significantly higher in the region with seismic intensity > VIII. Combined with the sedimentary distribution along-strike of the surface rupture, the mapped liquefaction sites indicate that the differences in the sedimentary environments could cause more intense liquefaction on the western side of the epicenter, where loose Quaternary deposits are widely spread. The stronger coseismic liquefaction sites correspond to the Eling Lake section, the Yellow River floodplain, and the Heihe River floodplain, where the soil is mostly saturated with loose fine-grained sand and the groundwater level is high. Our results show that the massive liquefaction caused by the strong ground shaking during the Maduo (Madoi) earthquake was distributed as the specific local sedimentary environment and the groundwater level changed.

A Case Study of Multidisciplinary Surface Faulting Assessment in the Urbanized Fucino Basin, Italy

The occurrence of coseismic surface ruptures along fault traces in urbanised areas creates a serious hazard to the vulnerability of man-made manufactures. In order to mitigate such hazard, it is necessary to investigate the geometry, the activity and the capability of faults located close to urbanised areas. This paper presents a case study of the investigation of capable faults within a sensitive area in Italy that is characterized by a high density of population and industrial activities, high levels of seismicity and the presence of faults proven to be capable of rupturing the surface during medium-to-large earthquakes. We focused on the Luco fault (Fucino basin, Central Italy), which previous studies have suggested to cross the industrial district of the town of Avezzano. We present a multidisciplinary approach, consisting of Electrical Resistivity Tomography surveys, continuous-coring boreholes and paleoseismological trenches, aimed at accurately constraining the trace of the Luco fault and documenting the associated fault displacement. This allowed us to constrain the geometry of the Luco fault and to assess the associated fault displacement hazard. We suggest that the proposed methodology represents a pilot study for further investigations of capable faults in the Italian and other similar seismotectonic contexts.

Active fault detection and characterization by ultrashallow seismic imaging: A case study from the 2016 Mw 6.5 central Italy earthquake

We present the first high-resolution ultrashallow seismic image of a normal fault segment that ruptured the surface during the Mw 6.5 2016 Norcia earthquake (central Italy). This is the only fault, in the entire activated 25 km-long system, cutting a thick succession of Quaternary deposits, with an associated 3-m-high cumulative scarp. A 190-m-long profile crossing the fault was acquired and analyzed combining reflection seismic, non-linear multiscale refraction P-wave tomography and multi-channel analysis of surface waves. The joint interpretation of the seismic reflection, P- and S-wave velocity images unravels a 100-m-thick sequence of sandy-gravel alluvial fans, disrupted by a main normal fault zone, named as Valle delle Fonti fault (Vf1), which branches upward into three splays. The eastern splay of Vf1 matches with the 2016 coseismic surface rupture. Near-surface truncated reflections and growth strata in the hanging wall of the western and intermediate splays attest to their activity in Late Pleistocene-Holocene times. We also detect an additional normal fault in the footwall of Vf1, probably inactive since the Late Pleistocene.Comparing the seismic images with the Poisson's coefficient model and with the results of a previous electrical resistivity tomography, we constrain the lithology and the hydraulic behavior of the uppermost 50 m of the fault. A steep, W-dipping zone with high-Vp, very high Poisson's coefficient and low resistivity correlates with the eastern splay of Valle delle Fonti fault and unravels a water-saturated region. These results suggest that the fault zone may act as a partial barrier for horizontal fluid flow. Our findings indicate that the active fault zone detected by seismic imaging is much wider than what previously estimated from surface geological analyses. In terms of surface faulting hazard, this study confirms the effectiveness of high-resolution seismic surveys in defining the geometry and physical properties of active fault zones.

Aerial Mapping of Coseismic Surface Rupture of 2021 Mw 7.3 Maduo Earthquake, China

The 2021 Mw 7.3 Maduo earthquake is one of the largest seismic events that has occurred in and around the Bayan Har block of Tibet. D-InSAR results and field surveys indicate that this earthquake resulted in more than 160 km of coseismic surface rupture along pre-existing fault traces. Based on the branching of the surface rupture, the fault of the Maduo earthquake can be roughly divided into four sections. Through detailed drone mapping, the fracture pattern and offset of the fault were counted and measured. The development of the peaty meadow layer on the ground determines the different combination modes of the fractures. The horizontal offset observed on the surface of this earthquake is generally less than 2 m and the vertical offset is less than 1 m, and the fault shows a primarily left-lateral strike-slip movement. In the desert-covered areas, there are long gaps between continuous rupture.