Paleoliquefaction Features Research Articles

Estimation of historical earthquake-induced liquefaction in Fraser River delta using NBCC 2020 GMPEs in deterministic and probabilistic frameworks

Paleo-liquefaction features of sand dykes and sand blows were identified in the 1990s at multiple host sediments in the Fraser River delta in southern British Columbia all younger than 3500 BP. These paleo-liquefaction sites could be linked to Cascadia subduction earthquakes. Empirical magnitude-bound relationships are often used to estimate paleo-earthquake magnitudes. To determine the lower bound magnitude of Cascadia interface earthquakes that could have generated the paleo-liquefaction features, we use ground motion prediction equations for interface earthquakes from the sixth Canadian seismic hazard model of the 2020 National Building Code of Canada. We estimate the minimum M and its peak ground acceleration ( amax) of an interface earthquake required to initiate paleo-liquefaction in the study region. Starting with three full-rupture deterministic scenarios of varying source-to-site distance, we determine the minimum M required from Cascadia subduction zone interface mega-thrust earthquakes to induce liquefaction in the Fraser River delta spans 8.0–8.9 with a corresponding amax range of 0.09–0.13 g. We also perform a back-calculation paleo-liquefaction analysis in a probabilistic framework to incorporate aleatory uncertainties (cone penetration resistance, groundwater table, and amax) and epistemic uncertainties (liquefaction simplified model) via the Monte Carlo simulation. The developed probabilistic methodology is also applicable to a forward liquefaction assessment and other liquefaction sites globally. The median M from this probabilistic paleo-liquefaction for the four investigated sites lies between 8.8 and 9.0. Our probabilistic results also reveal that Cascadia interface earthquakes with M > 8.9 lead to a 31%–57% probability of liquefaction triggering in the Fraser River delta. In addition, we developed deterministic and probabilistic magnitude-bound curves specific to Cascadia interface earthquakes and representative site class E conditions. These curves provide more accurate magnitude estimations for predicting seismic-induced liquefaction from Cascadia interface earthquakes for sites in the Pacific Northwest than empirical bound curves.

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.

Rapid Postearthquake Field Reconnaissance, Paleoseismic Trenching, and GIS-Based Fault Slip Variability Measurements along the Mw 6.4 and Mw 7.1 Ridgecrest Earthquake Sequence, Southern California

ABSTRACTUnderstanding fault rupture deformation patterns, especially in complex fault zones, has fundamental implications on seismotectonic studies and hazard mitigation for the built environment. The 2019 Mw 6.4 and Mw 7.1 Ridgecrest earthquake ruptures offer an opportunity to quantify deformation patterns and surface displacements from a complex fault rupture. Our field reconnaissance, within 18 hr of the Mw 6.4 event, documented a complex and relatively broad fault deformation zone up to a few kilometers wide in the vicinity of a gas transmission pipeline intersected by the surface rupture south of Highway 178. The subsequent Mw 7.1 event resulted in similarly distributed surface fault deformation within a broad zone that crossed a second gas transmission pipeline located south of Highway 178. On 10 July, fault-normal pipeline assessment trenches were excavated at both locations and provided evidence for late Pleistocene fault rupture on both faults expressed as upward fault truncations and paleoliquefaction features. Subsequent imagery-based rupture-mapping facilitated identification and measurement of offset features that were not identified during field mapping. Fault displacement measurements document a gradual decrease in fault slip on rupture southwestward from the Mw 6.4 epicenter within the study area. However, displacement along the primary Mw 7.1 rupture decreased more drastically southeastward toward a structural complexity at a fault stepover expressed as a horsetail splay. Fault-normal slip distributions showed that majority of the surface deformation was accommodated along discrete fault strands within the primary fault zone across both ruptures. This work expands the catalog of high-fidelity coseismic rupture information used to better understand seismotectonic processes, while contributing to refinement of fault displacement models used in support of critical infrastructure design.

Late Holocene Deformation near the Southern Limits of the Wabash Valley Seismic Zone of Kentucky and Indiana, Central United States, with Seismic Implications

ABSTRACTThe Wabash Valley seismic zone (WVSZ) is a region of diffuse, modern intraplate seismicity in the central United States with a history of strong, late Quaternary and Holocene seismicity as determined through paleoliquefaction studies. Yet, there are no specific faults linked to these strong WVSZ paleoearthquakes, some of which were as large as Mw 7.2–7.5. A multidisciplinary investigation of a linear, 5-kilometer-long and ∼3-meter-high scarp on the Ohio River floodplain in the southernmost WVSZ in western Kentucky evaluated whether the scarp is a fluvial landform or a tectonic feature. Geomorphic mapping and optically stimulated luminescence geochronology show that the age and orientation of the scarp are inconsistent with surrounding fluvial landforms. Trenching, core drilling, seismic reflection, electrical resistivity profiling, and cross sections of petroleum well logs all indicate a blind fault directly underlies the scarp. The scarp is interpreted to be the fold axis of a down-to-the-west monocline formed in alluvium by slip on the underlying blind fault, herein named the Uniontown fault. The Uniontown fault connects the Hovey Lake fault, striking N20°E and having ∼0.5 km of documented strike-slip offset, with an unnamed fault complex to the south that strikes N40°E, suggesting the Uniontown fault is part of a larger, Paleozoic structure that has been reactivated with strike-slip deformation. Geomorphic mapping utilizing luminescence and radiocarbon geochronology indicates that folding and faulting occurred ∼3.5 ka. Paleoliquefaction was suppressed by a thick clay cap in the main Ohio Valley, but paleoliquefaction features are widespread on Ohio River tributaries. Gravel dikes at one site had a maximum age of 3.4±0.4 ka, confirming the region has experienced strong, late Holocene shaking. Estimates using vertical displacement and rupture length indicate that slip on the Uniontown scarp could produce an Mw 6.2–7.7 earthquake, which is comparable to other large paleoearthquakes in the WVSZ paleoseismic record.

Evidence of prehistoric liquefaction in Kuwait and implications for the seismic vulnerability of the Arabian Gulf Countries

This paper presents and analyzes paleo-liquefaction features found in the State of Kuwait. The features are cemented sand and gravel-filled dikes of Pleisto–Holocene age with appearance and composition similar to typical “sandstone pipes.” The significant age difference between the cemented dikes and the surrounding loose sand, the size and spatial distribution of the dikes, and the local geologic and hydrologic setting all suggest that the feature probably results from a single large event of seismic origin. Likely hypotheses include shaking during large earthquakes or seiching of tsunami-like waves. Additional research is needed to identify the exact cause of these dike formations, which is important for the purpose of improving seismic risk and vulnerability assessment of the Arabian Gulf countries. The search may also help explain the disappearance of an ancient civilization that lived in the same region approximately seven thousand years ago.

Controls on patterns of liquefaction in a coastal dune environment, Christchurch, New Zealand

Liquefaction features in the geological record are important off-fault markers of moderate to large (>5 Mw) paleoearthquakes. The study of contemporary liquefaction features provides a better understanding of where to find past (paleo) liquefaction features which, if correctly identified and dated, can provide information on the occurrence, magnitude and timing of past earthquakes. This is particularly important in areas with blind active faults. This paper describes liquefaction features in the coastal setting of Christchurch (South Island of New Zealand), and explores the role of liquefaction and fluidization in the surface soil profile and their role in controlling surface ejection. The paper also compares the styles of liquefaction surface manifestation in the alluvial and coastal settings, and the role played by the sedimentary architecture in both environments. This analysis contributes to our understanding of which of the two environments provides a better target for paleoliquefaction studies, and which geomorphic setting within those environments is most likely to host paleoliquefaction features. The coastal setting (in particular, young coastal areas, <300 years old) is especially prone to liquefaction because near surface soils are dominated by well-sorted sandy aeolian deposits and a shallow water table exists. Fluidization within the near surface sandy layer that liquefied and in horizons above, due to upward moving pore water, resulted in a very disrupted soil stratigraphy, making it difficult to identify paleoliquefaction features. Therefore, young coastal areas are not the best target for identifying individual paleoliquefaction events. In comparison, the alluvial setting is characterized by sandy point-bar and channel deposits capped by cohesive overbank and abandoned-channel deposits. As a consequence, sand dikes that form in the alluvial settings are well defined, with preservation of the original soil stratigraphy and distinct cross cutting relationships. These conditions make the alluvial setting, along with older coastal deposits (>1000 years old), a better target for paleoliquefaction studies.

Liquefaction Induced during the 2010–2011 Canterbury, New Zealand, Earthquake Sequence and Lessons Learned for the Study of Paleoliquefaction Features

ABSTRACT Very large to moderate earthquakes in the 2010–2011 Canterbury sequence induced liquefaction in parts of Christchurch city and the surrounding region on the South Island of New Zealand. Detailed information gathered about this case of recurrent liquefaction offers important lessons for the study of paleoliquefaction features and the paleoearthquakes that caused them. The Canterbury case demonstrates that liquefaction features are important indicators of strong ground shaking in regions where fault ruptures do not necessarily propagate to the surface, may be masked by later sedimentation, or are otherwise difficult to recognize. Comparison of the liquefaction fields produced by the 2010 M 7.1 Darfield and 2011 M 6.2 Christchurch earthquakes in the Canterbury sequence highlights the influence of site conditions on the geographical distribution of liquefaction features and underscores the need to consider liquefaction susceptibility of sediment and depth of the water table when using paleoliquefaction features to interpret the source area and magnitude of paleoearthquakes. The epicentral distance and size of liquefaction features that formed during the Darfield and Christchurch earthquakes corroborate and further constrain empirical relations used to estimate source areas and magnitudes of paleoearthquakes. Formation of compound sand blows, composed of multiple sand–silt couplets resulting from repeated liquefaction during the Canterbury earthquakes, supports previous interpretations of compound sand blows in the central and western United States. In addition, paleoliquefaction features found in excavations of sand blows that formed during the 2010–2011 Canterbury earthquakes indicate that sites of modern liquefaction are prime targets for paleoliquefaction studies. The depositional environments where liquefaction features form and are preserved help to guide searches for paleoliquefaction features. Information from many sites across a region is needed to develop a chronology of past liquefaction events, to define their liquefaction fields, and to estimate the source areas and magnitudes of paleoearthquakes.

Liquefaction Features Produced by the 2010–2011 Canterbury Earthquake Sequence in Southwest Christchurch, New Zealand, and Preliminary Assessment of Paleoliquefaction Features

Liquefaction features and the geologic environment in which they formed were carefully studied at two sites near Lincoln in southwest Christchurch. We undertook geomorphic mapping, excavated trenches, and obtained hand cores in areas with surficial evidence for liquefaction and areas where no surficial evidence for liquefaction was present at two sites (Hardwick and Marchand). The liquefaction features identified include (1) sand blows (singular and aligned along linear fissures), (2) blisters or injections of subhorizontal dikes into the topsoil, (3) dikes related to the blows and blisters, and (4) a collapse structure. The spatial distribution of these surface liquefaction features correlates strongly with the ridges of scroll bars in meander settings. In addition, we discovered paleoliquefaction features, including several dikes and a sand blow, in excavations at the sites of modern liquefaction. The paleoliquefaction event at the Hardwick site is dated at A.D. 908–1336 , and the one at the Marchand site is dated at A.D. 1017–1840 (95% confidence intervals of probability density functions obtained by Bayesian analysis). If both events are the same, given proximity of the sites, the time of the event is A.D. 1019–1337. If they are not, the one at the Marchand site could have been much younger. Taking into account a preliminary liquefaction‐triggering threshold of equivalent peak ground acceleration for an M w 7.5 event (PGA7.5) of 0.07 g , existing magnitude‐bounded relations for paleoliquefaction, and the timing of the paleoearthquakes and the potential PGA7.5 estimated for regional faults, we propose that the Porters Pass fault, Alpine fault, or the subduction zone faults are the most likely sources that could have triggered liquefaction at the study sites. There are other nearby regional faults that may have been the source, but there is no paleoseismic data with which to make the temporal link. Online Material: Figures showing areas of liquefaction, trench logs, information on dike and sand‐blow parameters, dike azimuths, core logs, radiocarbon samples, and OxCal analysis, and tables detailing units exposed in the trenches and stereonets.

Development of magnitude-bound relations for paleoliquefaction analyses: New Zealand case study

Magnitude-bound relations are often used to estimate paleoearthquake magnitudes from paleoliquefaction data. This study proposes New Zealand-based magnitude-bound curves that are developed using (a) liquefaction field observations and (b) a newly proposed back-calculation approach that combines the simplified liquefaction evaluation procedure with a regionally appropriate ground motion prediction equation. For (b) both deterministic and probabilistic frameworks are proposed. The magnitude bound curves back-calculated using either the deterministic or probabilistic frameworks are advantageous in that they can be used to predict the spatial distribution of liquefaction in regions where historical liquefaction field observations are limited or poorly documented, and because soil- and site-specific conditions can be incorporated into magnitude-bound analyses. Moreover, curves developed using the probabilistic framework allow for the range of possible causative earthquake magnitudes to be better understood and quantified. To demonstrate the use of the proposed relations, paleoliquefaction features discovered in eastern Christchurch (NZ) are analyzed. The 1869 ~Mw4.8 Christchurch earthquake and/or 1717 ~Mw8.1 Alpine Fault earthquake are found to be the most likely candidates amongst known historical and paleoearthquakes for triggering liquefaction over the permissible time range (ca. 1660 to 1905 A.D.). This study demonstrates the potential of the proposed magnitude-bound curves to provide insight in to past, present, and future hazards, proving their utility even in cases of limited evidence. The approach of developing and applying magnitude bound curves proposed herein is not limited to parts of New Zealand, but rather, can be applied worldwide.

Earthquake Focal Mechanisms in the New Madrid Seismic Zone

Online Material: Table of focal mechanisms; color versions of figures. The occurrence of intraplate earthquakes is largely an unexplained phenomenon. The New Madrid Seismic Zone (NMSZ) lies within the interior of the North American plate and is approximately 2000 km from the nearest active plate boundary. Yet, it has produced sequences of large earthquakes with widespread and coincident areas of paleoliquefaction features: A.D. 900±100, A.D. 1450±150, and 1811, 1812 (Tuttle et al. , 2002). Several theoretical driving mechanisms of NMSZ intraplate earthquakes have been proposed (e.g., Grana and Richardson, 1996; Liu and Zoback, 1997; Kenner and Segall, 2000; Grollimund and Zoback, 2001; Pollitz et al. , 2001; Forte et al. , 2007; Tavakoli et al. , 2010; Calais et al. , 2010). A short summary of these driving mechanisms is available in Powell and Horton (2009). Our aim is to contribute earthquake focal mechanism solutions for the study of seismotectonics in this region. The dominant trends in strike of the nodal planes are compared with the orientations of major structures in the region. We also estimate the variation in crustal stress via stress inversion in the northern Mississippi embayment. The focal mechanism results from this study (Johnson, 2008) show a possible rotation of the regional horizontal compressive stress. For future studies, these results may serve as a constraint to physical models of deformation. Focal mechanisms in this study are grouped into four areas, herein referred to as segments, which relate dominant trends of focal mechanism nodal plane strike to localized areas of seismicity (Fig. 1). Two of these segments strike northeast–southwest and lie at the northern and southern ends of the NMSZ, having nearly vertical dip. These will be referred to as the northeastern segment (northern end) and southwestern segment. They are characterized by mainly strike‐slip events and …

Geophysical Imaging of Subsurface Earthquake-induced Liquefaction Features at Christchurch Boys High School, Christchurch, New Zealand

On February 22, 2011, a magnitude Mw 6.2 earthquake affected the Canterbury region, New Zealand, resulting in many fatalities. Liquefaction occurred across many areas, visible on the surface as “sand volcanoes”, blisters and subsidence, causing significant damage to buildings, land and infrastructure. Liquefaction occurred at a number of sites across the Christchurch Boys High School sports grounds; one area in particular contained a piston ground failure and an adjacent silt volcano. Here, as part of a class project, we apply near-surface geophysics to image these two liquefaction features and determine whether they share a subsurface connection. Hand auger results enable correlation of the geophysical responses with the subsurface stratigraphy. The survey results suggest that there is a subsurface link, likely via a paleo-stream channel. The anomalous responses of the horizontal loop electromagnetic survey and electrical resistivity imaging highlight the disruption of the subsurface electrical properties beneath and between the two liquefaction features. The vertical magnetic gradient may also show a subtle anomalous response in this area, however the results are inconclusive. The ground penetrating radar survey shows disruption of the subsurface stratigraphy beneath the liquefaction features, in particular sediment mounding beneath the silt ejection (“silt volcano”) and stratigraphic disruption beneath the piston failure. The results indicate how near-surface geophysics allow the characteristics of liquefaction in the subsurface to be better understood, which could aid remediation work following liquefaction-induced land damage and guide interpretation of geophysical surveys of paleoliquefaction features.

Field evidence of seismites in Quaternary deposits of the Jijel (Eastern Algeria) coastal region

Jijel has been hit by a strong earthquake in 1856 that triggered a destructive tsunami. Field geological investigations show that the marine terrace deposits (Tyrrhenian or likely Eutyrrhenian) exhibit several types of soft sediment deformation features including sismoslumps, thixotropic bowls, thixotropic wedges, and diapir-like structures. In addition, paleo-liquefaction features represented by neptunian and injection dikes have been observed in the sand dune deposits (Aterian or Wurm). Furthermore, typical paleo-earthquake-induced ground failures including lateral spreading, paleo-landslides, and sand volcanoes have been observed in recent, likely, Holocene deposits. Such features, remarkably comparable to present-day earthquake-induced ground failures showing clearly repetitive occurrence of past events may constitute a precious material for future paleo-seismic investigation. The various features have been interpreted herein as seismites associated to strong earthquakes produced likely by the potentially active faults previously identified in the area.

Eastern Section SSA 2011 Meeting Report

The 83rd Eastern Section SSA meeting was hosted by the University of Arkansas at Little Rock at the Peabody Hotel downtown Little Rock, Arkansas, 16–18 October 2011, during the lovely fall season of the mid-south. The meeting began with a field trip to east central Arkansas on a day with perfect weather on Sunday 16 October 2011. The field trip, led by Drs. Martitia Tuttle and Haydar Al-Shukri, was arranged to have the participants experience the paleoseismic features that have been preserved in the shallow subsurface for thousands of years. Thirty-three of the meeting attendees participated in the field trip, which was conducted from 9:00 am to 5:00 pm. To prepare for the field trip, a very wide trench was excavated using a 4-foot sand bucket backhoe at a site where multiple stacked sand blows along a lineament had been previously discovered. The large trench provided easy and safe access to paleoliquefaction features and allowed fieldtrip participants to examine them first-hand. In addition, the excavation of the sand blows provided an opportunity to improve age estimates of paleoearthquakes. Therefore, two dating samples were collected in association with the older, more poorly understood sand blow. During the field trip, we demonstrated field techniques, such as mapping of sand blows and related sand dikes with ground-penetrating radar (GPR), and we discussed observations and interpretations of paleoliquefaction features. Prior to trenching, we conducted GPR and resistivity surveys to help with the siting of the trench to optimize exposure of the paleoliquefaction features. Also, geophysical information was presented during the fieldtrip to educate participants about the usefulness of combining geophysics with trenching. As expressed by many participants, a major highlight of the meeting was the field trip. Photographs and other information are available at the meeting Web site (http://quake.ualr.edu/ES-SSA-Meeting-2011.htm). We appreciate the University …

The sinkhole enigma in the Alpine Foreland, Southeast Germany: Evidence of impact-induced rock liquefaction processes

AbstractSudden collapse of the Quaternary soil to form sinkholes on the order of meters and tens of meters has been a geologic phenomenon within living memory in a localized area north of Lake Chiemsee in Southeast Germany. Failing a satisfying explanation, a relation with an undefined glaciation process has always been proposed. Excavations and geophysical measurements at three newly affected sites show underground features such as prominent sandy-gravelly intrusions and extrusions typical of rock liquefaction processes well known to occur during strong earthquakes. Since strong earthquakes can reasonably be excluded to have affected the area under discussion, it has been suggested that the observed widespread liquefaction is related with the recently proposed Holocene Chiemgau meteorite impact event. Except for one earlier proposed but unassertive relation between impact and liquefaction, the obviously direct association of both processes in the Chiemgau area emphasizes that observed paleoliquefaction features need not necessarily have originated solely from paleoseismicity but can provide a recognizable regional impact signature.

Liquefaction caused by the 2009 Olancha, California (USA), M5.2 earthquake

The October 3, 2009 (01:16:00 UTC), Olancha M5.2 earthquake caused extensive liquefaction as well as permanent horizontal ground deformation within a 1.2 km 2 area earthquake in Owens Valley in eastern California (USA). Such liquefaction is rarely observed during earthquakes of M ≤ 5.2. We conclude that subsurface conditions, not unusual ground motion, were the primary factors contributing to the liquefaction. The liquefaction occurred in very liquefiable sands at shallow depth (< 2 m) in an area where the water table was near the land surface. Our investigation is relevant to both geotechnical engineering and geology. The standard engineering method for assessing liquefaction potential, the Seed–Idriss simplified procedure, successfully predicted the liquefaction despite the small earthquake magnitude. The field observations of liquefaction effects highlight a need for caution by earthquake geologists when inferring prehistoric earthquake magnitudes from paleoliquefaction features because small magnitude events may cause such features.

Conspicuous sediment structures in fossil beach deposits (southern Tenerife, Canary Islands, Spain): paleoliquefaction features versus biogenic origin

Tubular-shaped concretions and concretionary dykes occur in Holocene fossil beach deposits between the township of El Medano and Punta Roja in southern Tenerife, Canary Islands. These sediment structures have been interpreted either as the result of (a) the interaction between hot ignimbrites that overflowed wet beaches; (b) fast accumulation of beach sands on hot and degassing ignimbrites; (c) paleoliquefaction caused by an earthquake (seismites). Based on the interpretation as seismites, an intense paleoearthquake with a moment magnitude of M = 6.8 was proposed to be responsible for the generation of the paleoliquefaction structures. However, we here reinterpret the sedimentary structures in question using the general criteria diagnostic for rhizocretions and root tubules with respect to their orientation, size, branching system, and style of cementation and, thus, consider them, to be of biogenic origin.

Assessing the previous activity at the source zone of the 2001 Bhuj earthquake based on the near‐source and distant paleoseismological indicators

The Mw 7.7 2001 Bhuj (Kachchh) earthquake was not associated with any primary surface rupture, but it produced secondary faulting, folding and liquefaction. This study highlights the potential of a secondary rupture and proxies like lateral spreads and sandblows in unraveling the past activity related to the 2001 source. Chronological constraints of an older lateral spread and far‐field paleoliquefaction features, combined with archeological data, provide evidence for occurrences of two previous earthquakes at the 2001 source zone about 4000 and 9000 years, ago. Distinct stratigraphic evidence for at least one previous offset dated at 4424 ± 656 years could be detected at a stepover zone associated with a dextral secondary fault, reactivated during the 2001 earthquake. The studies imply longer interseismic intervals for the 2001 source zone, in comparison with the source zone of the 1819 earthquake located toward the northwestern part of the Rann of Kachchh. The spatial and temporal correlation of previous events derived on the basis of the available paleoseismic data from the region suggest not only repeated activity at the 2001 source, but possibility for additional potential sources in parts of Kachchh and Cambay basins. Although we infer a longer recurrence interval for the 2001 Bhuj earthquake source, our study points to the fact that these additional sources may have the potential to rupture in the future, considering the long elapsed time.

Restless Kansas: Evidence of Structural Development in the Flatlands

The Phanerozoic structural development of Kansas is recorded by the stratigraphic and sedimentological evidence. The early Paleozoic was relatively quiet, but a major change in the structural regimen took place in the late Paleozoic as a result of events in adjacent areas. Structural development was mainly by vertical differential movement along faults defining rigid Precambrian basement blocks as they adjusted to the stress. These movements are recorded in the changes of sediment thickness over the fault blocks. Concurrently, as the basement blocks adjusted, seismites were triggered by paleoearthquakes. By mapping the occurrence of seismites vertically and laterally, conclusions can be made on the frequency and intensity of the paleoquakes. The occurrence of seismites formed by paleoquakes seemingly diminish with time, but this may be a function of suitable conditions for their formation and preservation.Subsequent structural movement in the Mesozoic and Tertiary was mainly regional tilting, however, some convolute sedimentary structures and small intraformational faults in the Cretaceous indicate vertical movement was continuing. Paleoliquefaction features also have been reported in Holocene sediments in Edwards, Wabaunsee, and Woodson counties, Kansas. Historical recorded earthquakes and microseisms are evidence that the strain and structural movement is continuing today. Other than shallow man-made quakes, earthquake foci, in general seem to concentrate at two depths: 7.5 to 13.5km (Conrad discontinuity) and 35 to 50 km (Mohorovičić or Moho boundary). The major disturbances, for the most part, occur along the seismic active Nemaha Anticline from Nebraska to Oklahoma and the east-bounding Humboldt fault zone. From the available evidence, it is inferred that the structural development of Kansas is not and was not spectacular, but is and has been gradually continuous and intermittent.

Probabilistic methodology for the analysis of paleoliquefaction features

Paleoliquefaction features can be used to estimate lower bounds on the magnitude and ground motion associated with the earthquake that caused the liquefaction feature. The engineering back-analysis of paleoliquefaction features is usually conducted using state of the practice liquefaction-triggering analysis methodologies. Recent studies have shown that these methodologies are associated with variable probabilities of liquefaction depending on the soil parameters. This would imply that estimates of magnitude and ground motion intensity obtained from these methodologies would not be consistent for all soil sites. Moreover, these estimates could be unconservative. In this paper, the use of a probabilistic methodology for the back-analysis of paleoliquefaction features is proposed. The proposed methodology permits the incorporation of model and parameter uncertainty into the analysis and results in more robust estimates of past magnitude and a measure of the uncertainty associated with these predictions. Previously published paleoliquefaction data are used to demonstrate the applicability of the proposed method. Magnitude estimates obtained with the proposed method do not differ significantly from those obtained using deterministic methodologies, but the proposed methodology permits a quantification of the uncertainty associated with magnitude estimates.