Liquefaction Features Research Articles

Earthquake-triggered ground-failure inventory associated with the M7.1 2018 Southcentral Alaska earthquake

The 30 November 2018, magnitude (Mw) 7.1 earthquake in Southcentral Alaska triggered substantial landslides, liquefaction, and ground cracking throughout the region, resulting in widespread geotechnical damage to buildings and infrastructure. Despite a challenging reconnaissance and remote-sensing environment, we constructed a detailed digital inventory of ground failure associated with the event from several sources. Sources included information derived from remotely sensed data, and data compiled from literature, social media postings, and earthquake damage information compiled by local, state, and federal agencies. Each instance of ground failure within the inventory contains information on the location and type of observed ground failure, and the methods and data used to document the occurrence. Where high-quality data, such as LIDAR or satellite imagery, were available and showed the ground-failure instance clearly, the extent is mapped as a polygon or polyline. All other locations are mapped as points. There are a total of 886 ground-failure instances documented within the inventory (400 landslides, 286 liquefaction features, and 200 features unattributed to specific processes). A semi-quantitative confidence scheme is used to describe mapping certainty associated with each ground-failure feature. This inventory represents a relatively moderate ground-failure-triggering event that occurred in a subarctic environment. This data paper describes the content within the inventory, the inventory data collection procedures, and limitations of the data. Events of this type are not often documented in detail; thus, adding the inventory data to the US Geological Survey Open Repository of Earthquake-Triggered Ground-Failure Inventories further diversifies the datasets available to the scientific community to be used to better understand and model earthquake-triggered ground failure.

Environmental effects following a seismic sequence: the 2019 Cotabato—Davao del Sur (Philippines) earthquakes

In the period of October–December 2019, the Cotabato–Davao del Sur region (Philippines) was hit by a seismic sequence comprising four earthquakes with magnitude MW > 6.0 (EQ1-4; max magnitude MW 6.8). The earthquakes triggered widespread environmental effects, including landslides and liquefaction features. We documented such effects by means of field surveys, which we supplemented with landslide mapping from satellite images. Field surveys allowed us to gather information on 43 points after EQ1, 202 points after EQs2–3 and 87 points after EQ4. Additionally, we built a multi-temporal inventory of landslides from remote sensing, comprising 190 slope movements triggered by EQ1, 4737 after EQs2–3, and 5666 at the end of the sequence. We assigned an intensity value to each environmental effect using the environmental seismic intensity (ESI-07) scale. Our preferred estimates of ESI-07 epicentral intensity are VIII for the first earthquake and IX at the end of the sequence, which is in broad agreement with other events of similar magnitude globally. This study, which is the first case of the application of the ESI-07 scale to a seismic sequence in the Philippines, shows that repeated documentation of environmental damage and the evaluation of the progression through time may be useful for providing input data for derivative products, such as susceptibility assessment, evaluation of residual risk or investigation of the role played by ground shaking and by other mechanisms able to trigger environmental effects.

Soft sediment deformation structures from the Brahmaputra Basin: A window to the eastern Himalayan paleoseismicity and tectonics

The Brahmaputra foreland basin, is one of the most dynamic in terms of tectonism and sediment load, revealed a variety of seismically generated soft sediment deformation structures (SSDS) in the form of clastic dikes, sand sills and related micro-faults. The qualitative and quantitative parameters of these SSDS in the study area such as dimension, angle of intrusion to capping layer, cross-cutting relations, wall shattering, sand sills, and micro-faults seem to be caused by multiple strong seismic events. The causative earthquake with intensity (VIII-X), paleo-peak ground acceleration (0.55 g) and magnitude (M ≥ 7.0) might have caused liquefaction features in the study area. Along with the geometry of various SSDS and Optically stimulated luminescence (OSL) dates derived for the clastic dikes indicate the oldest possible age for the seismic event as 0.94 ka. Further, the intensity and age obtained for the present study indicates a possible near seismic source like Kopili Fault Zone, Mishmi Thrust, and neotectonic lineament with trend NW-SE, which can be traced as micro faults and in clastic dikes. Liquefaction potential studies in the area indicate the likelihood of very high liquefaction potential (>45) with ground failures regardless of earthquake size or epicentral distance. The present study highlights the importance of SSDS for establishing paleoseismology in tectonically active regions where surface ruptures are sporadic due to dense alluvial cover and most of the active faults are blind.

Semi-Supervised Learning Method for the Augmentation of an Incomplete Image-Based Inventory of Earthquake-Induced Soil Liquefaction Surface Effects

Soil liquefaction often occurs as a secondary hazard during earthquakes and can lead to significant structural and infrastructure damage. Liquefaction is most often documented through field reconnaissance and recorded as point locations. Complete liquefaction inventories across the impacted area are rare but valuable for developing empirical liquefaction prediction models. Remote sensing analysis can be used to rapidly produce the full spatial extent of liquefaction ejecta after an event to inform and supplement field investigations. Visually labeling liquefaction ejecta from remotely sensed imagery is time-consuming and prone to human error and inconsistency. This study uses a partially labeled liquefaction inventory created from visual annotations by experts and proposes a pixel-based approach to detecting unlabeled liquefaction using advanced machine learning and image processing techniques, and to generating an augmented inventory of liquefaction ejecta with high spatial completeness. The proposed methodology is applied to aerial imagery taken from the 2011 Christchurch earthquake and considers the available partial liquefaction labels as high-certainty liquefaction features. This study consists of two specific comparative analyses. (1) To tackle the limited availability of labeled data and their spatial incompleteness, a semi-supervised self-training classification via Linear Discriminant Analysis is presented, and the performance of the semi-supervised learning approach is compared with supervised learning classification. (2) A post-event aerial image with RGB (red-green-blue) channels is used to extract color transformation bands, statistical indices, texture components, and dimensionality reduction outputs, and performances of the classification model with different combinations of selected features from these four groups are compared. Building footprints are also used as the only non-imagery geospatial information to improve classification accuracy by masking out building roofs from the classification process. To prepare the multi-class labeled data, regions of interest (ROIs) were drawn to collect samples of seven land cover and land use classes. The labeled samples of liquefaction were also clustered into two groups (dark and light) using the Fuzzy C-Means clustering algorithm to split the liquefaction pixels into two classes. A comparison of the generated maps with fully and manually labeled liquefaction data showed that the proposed semi-supervised method performs best when selected high-ranked features of the two groups of statistical indices (gradient weight and sum of the band squares) and dimensionality reduction outputs (first and second principal components) are used. It also outperforms supervised learning and can better augment the liquefaction labels across the image in terms of spatial completeness.

Tracking surface and subsurface deformation associated with groundwater dynamics following the 2019 Mirpur earthquake

The Mirpur Mw 5.8 earthquake on September 24, 2019, produced extensive liquefaction-induced surface deformation (LISD) in the surrounding villages. Due to the complexity of seismic hazards and the occurrence of their effects on a large spatial scale, the resulting surface, and subsurface deformation are often poorly resolved. To cover spatially extended LISD, the PSInSAR technique provided subsidence and uplift rate values ranging from −110 to +145 mm/yr consistent with the spatial distribution of the mapped liquefaction features. The most prominent surface change occurred in Abdupur and Sang villages. GPR measurements were conducted to map the near-surface cracks produced by transported liquified sand into the shallow subsurface layers and other liquefaction features (elevated groundwater table, conductive clay pockets, fractures, sand dikes, and water-enriched zones). Thus, the GPR survey assisted in the reconstruction of these structural and hydrogeological features on the near surface. In addition, the highly vulnerable zones were identified and mapped using space- and ground-based remote sensing measurements supported by the field observations. The results highlight the effectiveness of the proposed novel approach for detailed assessment of the coseismic liquefaction-induced deformation on- and near-ground surfaces by identifying areas prone to failure during earthquakes and thereby can help with hazard mitigation.

The March 2020, Mw 5.7 Magna, Utah, earthquake—documentation of geologic effects and summary of new research

The March 18, 2020, Mw 5.7 Magna earthquake was the largest earthquake in Utah since the 1992 ML 5.8 St. George earthquake. The Magna earthquake occurred in the northwest corner of the Salt Lake Valley, home to 1.2 million people. Immediately following the earthquake, the Utah Geological Survey organized teams to collect perishable field data on the geologic effects of ground shaking near the epicenter, as well as establish a web-based digital clearinghouse to collect, distribute, and archive data related to the earthquake. This earthquake also coincided with the beginning of the COVID-19 global pandemic, which added extra challenges to our earthquake response. Teams used a small, unmanned aircraft system to obtain aerial photos and videos of geologic effects to supplement ground-based reconnaissance. The observed geologic effects of ground motions from the Magna earthquake include liquefaction in the form of sand boils, tension cracks, lateral spreading, and localized subsidence. No primary surface fault rupture was observed. The areas with the highest observed concentration of liquefaction features were close to the shore of Great Salt Lake and near the epicenter, northeast of the town of Magna. Photos and other documentation of the geologic effects associated with this earthquake are critical in helping to understand the hazards associated with moderate magnitude earthquakes in the Wasatch Front region. The earthquake sequence and associated geologic effects were well documented, due to the proximity to a major metropolitan area and the mainshock and aftershocks occurring within the densest part of the Utah Regional Seismic Network. In the two years since the earthquake, numerous studies have been published documenting and interpreting data to characterize the Magna event and discuss how new data add to what is known about seismic hazards along the Wasatch Front.

Classification and Semiquantitative Evaluation of Paleoearthquake Identification From Trenches on Normal Faults: A Case Study of Holocene Paleoearthquake Events From the Northern Margin of the Hetao Basin, China

AbstractLong paleoearthquake series are crucial for understanding the recurrence patterns of active faults and evaluating the seismic hazards of faults. In this study, the first semiquantitative evaluation of paleoearthquake events from trenches was applied to normal faults, and classification criteria for identifying paleoearthquakes in trenches on normal faults are proposed to demonstrate the feasibility of semiquantitative evaluations of paleoearthquake events on normal faults. In this study, 72 paleoearthquake trench sites on normal faults around the world were analyzed, and the main indicators for identifying paleoearthquakes on normal faults include the presence of vertical offset (VO), collapse wedge (CW), fissure (FIS), buried paleosol (BP), angular unconformity (AU), upward termination (UT), and sand liquefaction (LF) features. To describe and apply this semiquantitative evaluation method for paleoearthquake events on normal faults, 33 trenches for paleoearthquakes on a fault system in the northern margin of the Hetao Basin were comprehensively analyzed to determine Holocene paleoearthquake events on the Sertengshan, Wulashan, and Daqingshan piedmont faults, and the reliability of paleoearthquake events is discussed. The integrity of the paleoearthquake events obtained was tested by the displacement limit method. The Holocene paleoearthquake recurrence on the three faults was quasiperiodic; the coefficients of variation (COVs) were 0.44, 0.58, and 0.4.

The influence of sedimentary architecture on the formation of earthquake-induced liquefaction features: A case study in the New Madrid seismic zone

This study is aimed at understanding how the arrangement of fluvial sedimentary deposits and their physical properties influences the formation and location of liquefaction features resulting from earthquake strong ground motions. The study site is located in the Mississippi River floodplain in the New Madrid seismic zone of the central United States, an area that hosts abundant liquefaction deposits resulting from both historic and prehistoric earthquake sequences. We combine satellite imagery, electrical resistivity tomography, soil textural analyses and ditch exposures of liquefaction features to develop a model of how the spatial distribution of sedimentary deposits, such as point bars, overbank, levee, backswamp and channel-fill, contribute to pore pressure build-up and subsequent development of liquefaction features, such as sand dikes and sand blows, as water and entrained sediment forcefully flow toward the surface. The model helps to explain (1) the abundance of earthquake-induced liquefaction features present in the Mississippi River valley, where fine- to medium-grained saturated sands are interbedded with or overlain by fine-grained portions of channel-fill, levee, overbank or backswamp deposits, and (2) the concentration of liquefaction features along the margins of abandoned-channel fill, point bar and overbank deposits, as seen in other locations worldwide. This understanding can contribute to identifying areas where liquefaction may be a threat to engineered structures and limiting the extent of areas in which detailed engineering geology measurements (e.g., in situ testing) may be necessary.

Identification of active deformation zone associated with the 28th April 2021 Assam earthquake (Mw 6.4) using the PSInSAR time series

The co-seismic deformation of the 28th April 2021 Assam earthquake with a magnitude of 6.4 has been investigated using the Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR). The results obtained from the PSInSAR are validated with the results of the Global Positioning System (GPS). It is observed that the co-seismic deformation of the earthquake is not visible because of the atmospheric noise. Therefore, we used the Sentinel-1 time-series data of the area to minimize the atmospheric noise effect the data using the Atmospheric Phase Screening (APS) processing of Sentinel-1 time series data. The time-series analysis shows minor changes that occurred during the earthquake. Firstly, the detection of coherence-based changes was carried out to identify the most affected areas, caused by the earthquake. The results of time series analysis suggest that the region located to the north of the Brahmaputra River is subsiding at a much faster rate (−25 to -75 mm/y) than its southern counterpart, where the southern part is subsiding with an average velocity of −0.1 to −15 mm/y. The subsided locations identified using the PSInSAR are further confirmed by the presence of liquefaction features, ground cracks, and tilted buildings related to post-liquefaction ground settlement. To see the deformation along the Bomdila Fault (BF), re-analysis of the available GPS results has been carried out and the derived results reveal a significant amount of deformation (∼4 mm/y) associated with BF and Jorhat Fault (JF); whereas the deformation associated with Kopili Fault (KF) is 3.14 mm/y. Further, our results suggest the presence of compressional strain in the BF zone, while extensional strain in the KF zone. The earthquake focal mechanism analysis suggests that the event of the April 2021 was primarily associated with the BF rather than the KF.

The influence of alluvial stratigraphic architecture on liquefaction phenomena: A case study from the Terre del Reno subsoil (southern Po plain, Italy)

Earthquake-induced liquefaction phenomena are commonly observed at shallow depths or at the ground surface above Holocene alluvial deposits. Nonetheless, a high-resolution examination of the relationship between surface manifestations and alluvial stratigraphy has been rarely attempted. In this study, we provide a detailed subsurface model from a selected sector of the southern Po Plain affected by widespread liquefaction processes triggered by the 2012 Emilia-Romagna seismic crisis. We report a comprehensive sedimentological and CPT-based characterization of the Terre del Reno subsoil and investigate how the stratigraphy controls earthquake-induced liquefaction phenomena. The main facies associations making up the alluvial subsoil constitute the basic elements of the liquefaction system, herein named host, source and sedimentary cap. Their subsurface distribution documents the presence of fluvial bodies prone to liquefaction beneath the earthen levees and across an area dominated by flat muddy floodplain deposits with no physical evidence of paleochannels at the surface. In addition, our observations suggest that vertical and lateral changes in stratigraphy control the mode and location of liquefaction evidence at the surface in both settings. In particular, the relative thickness of fluvial channel bodies vs. channel levee deposits (source–seal couplet) appears to control the severity of sand ejection at the surface. Our findings also suggest that vertical and lateral discontinuities within source layers prevent the occurrence of widespread liquefaction features. Conversely, lateral spreading effects and differential underground hydrostatic pressure at the interface between saturated and less permeable units are accountable for repeated sand ejection along surface fractures. This case study constitutes a unique natural laboratory thanks to the quality and density of available data. However, we emphasize that a similar approach can be useful to promote source-layer identification in areas characterized by poor or sparse data and to mitigate liquefaction hazards in urban areas built on alluvial plains.

Liquefaction hazard assessment in a seismically active region of Himalayas using geotechnical and geophysical investigations: a case study of the Jammu Region

The Jammu Region (JR) in the northwestern Himalayas trigged by medium to high magnitude near-field as well as far-field earthquake events, including the most recent 2019 Mirpur earthquake. In this paper, an attempt has been made to develop the zonation map for liquefaction hazard in the JR based on liquefaction potential index (mathrm{LPI}) and probability of liquefaction ({P}_{L}). To achieve this, factor of safety against liquefaction was estimated using standard penetration test (SPT) data collected from geotechnical consultancies and shear wave velocity measured during field testing at 243 locations, and an integrated liquefaction hazard map generated. The liquefaction features such as sand blows and ground rupture were found in Jatah (Samba district) and Simbal (Jammu district). According to the integrated hazard map, places near the bank of Tawi River and Ravi River in Jammu have young alluvium, making them particularly prone to liquefaction. Liquefaction does not occur in the eastern and western sections because of high shear wave velocities and rock at shallow depth, and it also does not occur in the central area due to thick sand deposits. mathrm{LPI} values ranged from 0 to 27.45 having very low to very high liquefaction risk. {P}_{L} is greater than 0.75 for sites located on the southwestern side due to uniformly graded soil having extremely low SPT (N) and {V}_{s} values. This study will aid site planners in the construction of structures that consider liquefaction mitigation and well-defined liquefaction risk measures.

Synthetic modeling and field GPR survey to understand the near-surface deformation induced by coseismic groundwater dynamics following the 2019 Mirpur earthquake in Pakistan

The Mirpur earthquake of Mw 5.8 on 24 September 2019 severely damaged villages in the epicentral area. The earthquake-triggered ground dynamics produced widespread liquefaction features on the surface (e.g., fractured road structure and sand boils) and in the shallow subsurface (e.g., elevated groundwater table, fractures, and sand dikes). Due to complexity of liquefaction-induced deformation and timing of field surveys, the structural and hydrogeologic features that develop in the near surface during seismic events are often poorly resolved on ground-penetrating-radar (GPR) profiles. To track and delineate the internal architecture and coseismic changes in groundwater levels and/or pressures due to liquefaction, a GPR survey was carried out soon after the Mirpur earthquake. The sudden pore water pressure changes in the shallow aquifer system caused a rise in the water table via upward groundwater movement and fracturing followed by rapid infiltration. This cascade phenomenon has adverse effects on soil, water resources, civil infrastructure, and public health and safety. To better understand induced changes in the physical properties of road infrastructure and the shallow subsurface, we performed synthetic modeling of electromagnetic wave propagation by employing the finite-difference time-domain method. Based on the available information at multiple scales (borehole and geophysical), subsurface physical models representing the most common and important coseismic features were considered for synthetic modeling. Likewise, synthetic tests of paved road were conducted to simulate the radar response of structural discontinuities (fractures) developed at different angles. To validate synthetic results by identifying a similar dynamic response of the induced hydrogeologic changes in the form of coseismic liquefaction features, a field GPR survey was conducted. Our results clearly demonstrate that the GPR technique is a potential candidate for hydrogeophysical detection and characterization of features of interest in the case of paved roads as well as agricultural and residential areas. Additionally, the successful application of GPR proves it to be a cost-effective, high-resolution, and speedy tool for better assessment of hydrogeologic hazard, socioeconomic consequences, and mitigation in the Mirpur area. The proposed approach may find applications in other seismically active regions around the world.

Centrifuge modelling of wave-induced seabed response in clay

This paper describes a programme of centrifuge tests investigating the behaviour of clayey seabed under wave loading using an in-flight wave loading system. Three model seabeds of kaolin clay capturing typical unconsolidated, normally consolidated and overconsolidated soil responses were considered, with each seabed experiencing several episodes of wave loading and resting. Data acquisition measures included pore pressure transducers, accelerometer, bender elements and T-bar penetrometers. The depth-wise distribution of excess pore pressure, soil strength and modulus, as well as the motion of the liquefied layer of the seabed, was monitored throughout to enable a thorough investigation into the liquefaction and reconsolidation features of the soil. For the unconsolidated and normally consolidated soils, remarkable development of residual pore pressure was observed, and there was evidence that the strength/modulus recovery cannot be achieved by the surficial soil within a prototype time of 15 days. Within a certain depth below this surficial layer, there was a drastic increase in undrained strength, and this phenomenon was carefully examined by a modified moving-boundary model. For the overconsolidated soil, the build-up of residual pore pressure was rather limited, but discernible amplification of oscillatory pore pressure amplitude was observed. Implications for practice in offshore engineering are discussed based on the experimental findings.

Environmental effects and seismogenic source characterization of the December 2020 earthquake sequence near Petrinja, Croatia

SUMMARYOn 29 December 2020, a shallow earthquake of magnitude Mw 6.4 struck northern Croatia, near the town of Petrinja, more than 24 hr after a strong foreshock (ML 5). We formed a reconnaissance team of European geologists and engineers, from Croatia, Slovenia, France, Italy and Greece, rapidly deployed in the field to map the evidence of coseismic environmental effects. In the epicentral area, we recognized surface deformation, such as tectonic breaks along the earthquake source at the surface, liquefaction features (scattered in the fluvial plains of Kupa, Glina and Sava rivers), and slope failures, both caused by strong motion. Thanks to this concerted, collective and meticulous work, we were able to document and map a clear and unambiguous coseismic surface rupture associated with the main shock. The surface rupture appears discontinuous, consisting of multi-kilometre en échelon right stepping sections, along a NW–SE striking fault that we call the Petrinja-Pokupsko Fault. The observed deformation features, in terms of kinematics and trace alignments, are consistent with slip on a right lateral fault, in agreement with the focal solution of the main shock. We found mole tracks, displacement on faults affecting natural features (e.g. drainage channels), scarplets and more frequently breaks of anthropogenic markers (roads, fences). The surface rupture is observed over a length of ∼13 km from end-to-end, with a maximum displacement of 38 cm, and an average displacement of ∼10 cm. Moreover, the liquefaction extends over an area of nearly 600 km2 around the epicentre. Typology of liquefaction features include sand blows, lateral spreading phenomenon along the road and river embankments, as well as sand ejecta of different grain size and matrix. Development of large and long fissures along the fluvial landforms, current or ancient, with massive ejections of sediments is pervasive. These features are sometimes accompanied by small horizontal displacements. Finally, the environmental effects of the earthquake appear to be reasonably consistent with the usual scaling relationships, in particular the surface faulting. This rupture of the ground occurred on or near traces of a fault that shows clear evidence of Quaternary activity. Further and detailed studies will be carried out to characterize this source and related faults in terms of future large earthquakes potential, for their integration into seismic hazard models.

An Appraisal of Ground Failure and Hydrogeological Changes Associated with the 28 April 2021 Mw 6 Sonitpur Earthquake, Assam, India, Using Field Evidences and InSAR Measurements

Abstract Widespread damage and coseismic ground disturbances are generally associated with large magnitude and/or shallow focus earthquakes. Surprisingly, a deep focus (34 km), moderate magnitude earthquake (Mw 6) occurred near the Kopili fault zone in Sonitpur district, Assam, India, on 28 April 2021 and created intense ground shaking and extensive damage along the Brahmaputra Valley. We undertook a field survey within a day after the earthquake and carried out Interferometric Synthetic Aperture Radar (InSAR) analysis to map any coseismic ground deformation features. Our field survey revealed extensive liquefaction features and several coseismic secondary ground cracks along the alluvial tracts of the Brahmaputra River system. InSAR analysis revealed a sinistral slip up to ∼60 mm along a north-northwest–south-southeast-oriented previously unmapped lineament or fault. Field investigations revealed coseismic hydrological changes including a sudden rise and fall in the water level by 0.3–0.5 m followed by the injection of sand materials up to a thickness of 1.25 m in dug wells and the appearance of water in seasonally dried river channels and ponds. Interferometric coherence analysis during pre-, co-, and postseismic periods further confirmed the coseismic surge in water at five major tributary rivers of the Brahmaputra River. We speculate that the pressure difference at the shallow unconfined aquifer system of the mountain-front alluvial fan induced by coseismic stresses must have caused channeling of groundwater to the rivers and the contemporaneous water level fluctuations in wells. Amplification of seismic waves at the thick, unconsolidated sedimentary strata of the Brahmaputra Valley could have enhanced the extensive damage due to the 2021 Sonitpur earthquake. The present study has implications in estimating damage potential along the Brahmaputra Valley for future earthquakes.

Floodplain evolution and its influence on liquefaction clustering: The case study of March 2021 Thessaly, Greece, seismic sequence

The March 2021 Thessaly, Central Greece, seismic sequence characterized by an Mw = 6.3 mainshock and five Mw > 5.0 aftershocks triggered extensive liquefaction in the floodplain of the Piniada Valley and localized phenomena along the riverbanks of the Titarissios River. In order to document these secondary effects, we carried out immediate post event surveys based on remote sensing techniques and field-based reconnaissance. The initial desktop-based approach succeeded in delineating in advance the extensive liquefaction surface manifestations and in saving time for the subsequent field survey. The field work was performed with ground-based surveys, and UAV aerial campaigns. The longest reported linear liquefaction feature was 26.7 m, while the total sand blow covered an area of 0.0325 km2. Over one of the liquefaction manifestations, we performed parallel 2D electrical resistivity tomography profiles in order to reconstruct the subsoil stratigraphy. The produced 3D resistivity model successfully detects and illustrates the subsurface disruption following the generation of liquefaction. From the comparison between the spatial distribution of liquefaction phenomena and the geomorphological conditions in the area, the direct influence of the historical evolution of Pinios River in clustering liquefaction phenomena was highlighted. Thus, it is confirmed that a detailed investigation of the historical and late Holocene evolution of a floodplain i.e., location of ox-bow lakes, meanders and former river channels, can identify sites prone to liquefaction. This could result in a reduction of the area where detailed engineering geology investigations (e.g., boreholes with in-situ tests) are required for the evaluation of the liquefaction hazard.

Near-Field High-Resolution Maps of the Ridgecrest Earthquakes from Aerial Imagery

Abstract High-resolution maps of surface rupturing earthquakes are essential tools for quantifying rupture hazard, understanding the mechanics of rupture propagation, and interpreting evidence of past earthquakes in the landscape. We present highly detailed maps of five portions of the surface rupture of the 2019 Ridgecrest earthquakes, derived from 5 cm per pixel aerial imagery and 2–20 cm per pixel unmanned aerial vehicle imagery. Our high-resolution maps cover areas of complexity and distributed deformation, sections in which strain is very localized, and areas where the rupture breaks through sediment and bedrock, ensuring sampling of the diverse rupture styles of this earthquake sequence. These maps reveal the near-field deformation of the surface rupture with a high level of detail, resolving the extent of secondary fracturing, lateral spreading, and liquefaction features that are below the resolution of airborne lidar data, field mapping, and geodesy. These data may serve as a machine learning training dataset, and offer opportunities for detailed kinematic analysis and high-resolution probabilistic displacement hazard analysis.

Using paleo-liquefaction features to determine the likely source, magnitude and ground accelerations of pre-historic earthquakes in the Kashmir Basin (Northwestern Himalaya), India

Few surface fault scarps or other obvious surficial geomorphic features record pre-historic earthquakes in the Kashmir Basin (KB) in the northwestern Himalaya Mountains of India. We therefore identified liquefaction features exposed in various cuts and trenches in the area, documented these on geological logs, and geotechnically characterized them in order to determine the likely causative earthquake(s), the source area, the inferred paleo-magnitude and the relative ground accelerations. We calculate that the magnitude of liquefaction-producing earthquakes in the KB ranged between 6.4 and 7.3 Mw, and that the peak ground accelerations were on the order of 0.29–0.64 g. We propose that the techniques employed, the data obtained and the technical interpretations, are potentially useful, not only for local general landuse planning and site-specific hazard reduction, but may also be extrapolated to similar tectonically active regions.

The Liquefaction Record of Past Earthquakes in the Central Virginia Seismic Zone, Eastern United States

AbstractFollowing the 2011 moment magnitude, M 5.7 Mineral, Virginia, earthquake, we conducted a search for paleoliquefaction features and found 41 sand dikes, sand sills, and soft-sediment deformation features at 24 sites exposed in cutbanks along several rivers: (1) the South Anna River, where paleoliquefaction features were found in the epicentral area of the Mineral earthquake and farther downstream to the southeast; (2) the Mattaponi and Pamunkey Rivers east of the Fall Line, where liquefiable sediments are more common than in the epicentral area; and (3) the James River and Rivanna River–Stigger Creek, where a few sand dikes were found in the 1990s. Liquefaction features are grouped into two age categories based on dating of host sediment in which they occur and weathering characteristics of the features. A younger generation of features that formed during the past 350 yr are small, few in number, and appear to be limited to the James and Pamunkey Rivers. Though there are large uncertainties in their locations and magnitudes, one or more preinstrumental earthquakes, including the 1758, 1774, and 1875 events, likely caused these features. An older generation of liquefaction features that formed between 350 and 2800 yr ago are larger, more numerous, and more broadly distributed than the younger generation of features. Several earthquakes could account for the regional distribution of paleoliquefaction features, including one event of M 6.25–6.5 near Holly Grove, or two events of M 6.0 near Mineral and M 6.25 near Ashland. Amplification of ground motions in Coastal Plain sediment might have contributed to liquefaction along the Mattaponi and Pamunkey Rivers.

Seismically-Induced Soft Sediment Deformation Structures In and Around Chamoli, Garhwal Himalaya, India

Soft-sediment deformation structures were identified along Nandakini River valley near Chamoli village of Garhwal Lesser Himalaya. The deformation, in each outcrop, is restricted to a single stratigraphic layer bounded by undeformed flat-lying layers, eliminating the influence of slope failure. The structures are multiple liquefaction features like sand dikes, flame structures, pear-drop disturbance and downward warping of beds. The preferred interpretation is that the deformations resulted from earthquake-induced liquefaction and their existence adjacent to the Nandaprayag Fault can be related to episodic seismicity that occurred along this fault. However, more data and dating technique is needed to constrain the timing and distance to the causative seismic source. It is possible that more than one earthquake has effected the deformations.