Magnitudes Of Paleoearthquakes Research Articles

Magnitudes and surface rupture lengths of paleo-earthquakes at the NW-part of the Peel Boundary fault zone, Roer Valley Rift System

The Peel Boundary Fault zone (PBFZ) is the 125 km long, seismically active, northern bounding fault zone of the Roer Valley Rift System (RVRS). The last damaging earthquake along the PBFZ was the Roermond earthquake of 1992. It had a magnitude of Mw 5.3 and no surface rupture. Previous results from two trenching studies located in the central and southeastern parts of the PBFZ provided evidence for two surface rupturing paleo-earthquakes. The largest earthquake had an estimated magnitude of Mw ∼6.8 and a surface rupture length of at least 35 km. As it took place around the Late Pleniglacial – Late Glacial transition a link to glacio-isostatic motions is likely. Results from a new trench situated at the northwestern part of the PBFZ shows evidence for three to four paleo-earthquakes, of which three were surface rupturing. These comprise two normal faulting- and one, younger trans-tensional displacement. The normal faulting events have ∼1 m vertical displacements each, which translate into magnitudes of Mw ∼7. Like the previous results, they occurred during the Late Pleniglacial-Late Glacial transition, at ∼15 ka and ∼ 14 ka. The younger trans-tensional event occurred sometime during the Holocene, pre-dating an unaffected, 13th century man-made paleo-channel on the hangingwall. The potential fourth, non-surface rupturing earthquake is indirectly evidenced by loading deformations of a sand layer and a collapsed brick-wall in the infill of the paleo-channel. Comparison of our trenching results to those from the two previous studies, which were located farther to the southeast along the PBFZ, shows that for one event a correlation is possible. The correlation would indicate a surface rupture length of at least 55 km. Combined, all trenching results indicate that the characteristic maximum rupturing displacement is ∼1 m, and thus that Mw ∼7 is the maximum magnitude of paleo-earthquakes along the PBFZ.

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.

New Insights Into the Paleoseismic History of the Mae Hong Son Fault, Northern Thailand

The Mae Hong Son Fault (MHSF) is a north-trending active fault in northern Thailand. The largest earthquake ever recorded in Thailand occurred in February 1975 with a magnitude of 5.6 and was associated with the southern end of the MHSF. Paleoearthquake magnitudes, recurrence intervals, and slip rates for the MHSF are evaluated using the morphological characteristics of the MHSF aided with a 12.5-m-resolution digital elevation model (DEM) and using fault trenching. Morphotectonic analysis, including studies of offset streams, linear valleys, triangular facets, and fault scarps, helps illustrate dextral fault movements within the MHSF zone. Two separated N–S trending basins, the Mae Hong Son to the north and the Mae Sariang to the south, are present along the MHSF. Between these basins, fault displacements decrease toward the Khun Yuam area. Surface rupture length investigation from fault segments in both basins indicates maximum credible earthquake magnitudes between 5.8 and 6.3. Fault trenching and road-cut studies show that nine earthquakes occurred along the MHSF over the past ∼43 ka. Optically stimulated luminescence (OSL) dating help define the timing of the earthquakes to ∼43, ∼38, ∼33, ∼28, ∼23, ∼18, ∼13, ∼8, and ∼3 ka. The recurrence interval of earthquakes on the Mae Hong Son Fault is ∼5,000 years and the fault has a slip rate of ∼0.04–0.15 mm/a.

Surface trace of the active Katrol Hill Fault and estimation of paleo-earthquake magnitude for seismic hazard, Western India

Estimation of seismogenic potential through geological studies of faults is an important step in seismic hazard evaluation and mitigation. We investigated the Katrol Hill Fault (KHF), an E-W trending and south dipping high angle reverse fault in the seismically active Kachchh Basin at the western continental margin of India. While several faults in the eastern part of the basin are presently seismically active, the KHF is the only fault in the entire basin that is shown to have produced three Late Quaternary surface faulting events. We illustrate here an integrated geological approach using field mapping, microscopic analysis (petrography and quartz surface textures using SEM) and shallow geophysical surveys using GPR for determining the precise surface trace of the active KHF. We also determined the displacement and slip-rate for each surface faulting event. Based on the Late Quaternary surface faulting parameters deduced, we calculated the moment magnitude (Mw) of the events using well established empirical relationships. These calculations yielded Mw values consistently ≥ 6.5. Our study shows that the KHF is capable of producing high magnitude earthquakes. We infer that these surface faulting events may be of relatively shallow focus as higher magnitude earthquakes in recent times along other faults in the basin, except the 1819 Allahbund earthquake, did not produce surface rupture. We recommend a revision of seismic hazard risk and mitigation strategies of the region as a consequence of our findings.

The paleoearthquakes of the Langshan Piedmont fault, North China since late Pleistocene

The Langshan Piedmont fault (LPF) is an active Holocene normal fault that borders Langshan Mountain and the Hetao Graben in the northwest of Ordos Block of China. In this study, paleoseismic trenching was undertaken at three sites and 11 fault outcrops are well exposed. The results show that eight paleoearthquake events occurred on the LPF since 43 ka BP, and six paleoearthquake events are complete since 14 ka BP, the latest event is 2300–2400 a BP; the LPF has the characteristic of quasi-periodic recurrence and the average recurrence interval is 2350 years. Therefore, there is a high probability that the LPF will have another earthquake. The vertical activity rate of the LPF is ~1.12 ​mm/yr since Holocene, and ~0.77 ​mm/yr since 14 ka BP. In this study, it is considered that the LPF is mainly characterized by simultaneous rupture of the whole segment. The vertical displacement of the paleoearthquake events is 0.8–2.5 ​m and the corresponding maximum paleoearthquake magnitude is M 7.4. The seismic hazard of Langshan area should not be ignored. The buildings in Langshan area, especially Wulatehouqi and Qingshan town, should be able to withstand a magnitude 8 earthquake.

Late Quaternary displacements along the Zunduk fault according to ground-penetrating radar and morphostructural analysis (northwestern coast of Lake Baikal)

The article considers the results of GPR studies of the Zunduksky fault section activated between the Cape Oto-Khushun and the Zunduk River, activated in the late Quaternary. The aim of this work is to clarify the kinematic type, determine the vertical displacement amplitudes, and dip angles of the Zunduksky active fault activated in the late Quaternary, as well as determine the maximum magnitude of the earthquake that could occur as a result of the activation of the fault. The work was carried out by OKO-2 GPR with a shielded antenna AB-90 and ABDL-Triton. In addition to the main method, morphostructural analysis of the ledge was used. As a result of the work performed, it was found that the Zunduksky fault in the Late Quaternary was activated under tectonic extension with predominant fault displacement kinematics. The one-act vertical displacements along the seismic fracture change from SW to NE from 6.9 to 1.6 m. When the Late Quaternary ledge of the Zunduksky fault formed, the plastic component of the displacement had a certain value, the contribution of which is from 18 to 78 % of the total displacement. Paleo-earthquake magnitudes calculated from the maximum vertical displacement are Mw = 7.3 and Ms = 7.5.

Improving Paleoseismic Earthquake Magnitude Estimates with Rupture Length Information: Application to the Puget Lowland, Washington State, U.S.A.

ABSTRACTBoth earthquake displacement and rupture length correlate with magnitude, and, therefore, observations of each from past earthquakes can be used to estimate the magnitude of those earthquakes in the absence of instrumental records. We extend the Bayesian inversion method of Biasi and Weldon (2006), which estimates paleoearthquake magnitude from displacement observations, to incorporate both rupture length and surface displacement measurements into the magnitude inversion. We then use this method on 27 late-Pleistocene to Holocene paleoearthquakes in the Puget Lowland region of Washington. Observations of (typically vertical) fault separation per event range from 0.6 to 7 m, implying net displacement per event of up to 10±4 m for the largest event. Rupture lengths are estimated to vary between the smallest contiguous mapped scarps to the full extent of the faults mapped from geology and geophysical observations. Although, a few of the ruptures may be longer than 150 km, the ruptures have a median of 53 km, indicating that earthquakes in the Puget Lowland have relatively high displacement-to-length ratios. By considering both datasets, we find that all events were between M 6.3 and 7.5, generally consistent with the expected seismicity from the U.S. Geological Survey National Seismic Hazard Map for the region. The simultaneous use of both length and displacement data in the magnitude inversion decreases both the estimated earthquake magnitudes and the uncertainty. The magnitude reduction, in particular, is due to the relatively short rupture lengths possible for Puget Lowland faults. This implies a decrease in the seismic hazard (relative to a displacement-only assessment) to a highly populated and rapidly urbanizing region.

Earthquake surface ruptures on the altiplano and geomorphological evidence of normal faulting in the December 2016 (Mw 6.1) Parina earthquake, Peru

The 2016 Mw 6.1 Parina earthquake ruptured a shallow-crustal normal fault within the high Andes of south Peru. We use high-resolution DEMs and field mapping of the surface ruptures generated by the earthquake, in combination with co-seismic and post-seismic InSAR measurements, to investigate how different features of the geomorphology at Parina are generated by the earthquake cycle on the Parina Fault. We systematically mapped 12 km of NW-SE trending surface ruptures with up to ~27 cm vertical displacement and ~25 cm tensional opening along strike, separated by a gap with no observable surface ruptures. Co- and post-seismic InSAR measurements require slip below this gap in surface ruptures, implying that surface offsets observed in paleoseismic trenches may not necessarily be representative of slip at seismogenic depths, and will typically yield an underestimate of paleo-earthquake magnitudes. The surface ruptures developed along 10–20 m high cumulative scarps cutting through late Quaternary fluvio-glacial deposits and bedrock. The 2016 Parina earthquake did not rupture the full length of the late Quaternary scarps, implying that the Parina Fault does not slip in characteristic, repeat earthquakes. At Parina, and across most of the Peruvian Altiplano, normal faults are most-easily identified from recent scarps cutting late Quaternary moraine crests. In regions where there are no recently-deposited moraines, faults are difficult to identify and lack time constraints to quantify rates of fault slip. For this reason, current fault maps may underestimate the seismic hazard in the Altiplano.

Late Quarternary displacements along the Sarma segment of the Primorsky fault based on gpr survey data (Baikal rift)

Ground-penetrating radar (GPR) surveys were performed in the Sarma segment of the Primorsky fault between the settlements of Shida and Kurma. This segment belongs to one of the largest structures of the Baikal rift and was active in Late Quaternary (Early Holocene). The study aimed to reconstruct vertical displacement amplitudes and dip angles of fractures along the fault segment, clarify its kinematic type, and estimate a maximum magnitude of earthquakes that may occur in the study area. The GPR equipment set included an OKO-2 georadar and AB-250M and ABDL-Triton shielded antennas. The GPR surveys were supported by morphostructural and tectonophysical methods. Based on the interpretation of the geophysical survey data and satellite images, faults associated with the Sarma paleoseismic dislocation were mapped. Their total length amounts to 14 km. According to the GPR survey data, one-stage vertical displacements show normal faulting and vary from SW to NE from 4.4 to 7.7 m. Paleo-earthquake magnitudes calculated from the maximum displacement values (Mw=7.2, and Мs=7.4) suggest that potential earthquakes in the Primorsky fault zone may be stronger than previously assumed.

Paleoliquefaction Studies and the Evaluation of Seismic Hazard

Recent and historical studies of earthquake-induced liquefaction, as well as paleoliquefaction studies, demonstrate the potential usefulness of liquefaction data in the assessment of the earthquake potential of seismic sources. Paleoliquefaction studies, along with other paleoseismology studies, supplement historical and instrumental seismicity and provide information about the long-term behavior of earthquake sources. Paleoliquefaction studies focus on soft-sediment deformation features, including sand blows and sand dikes, which result from strong ground shaking. Most paleoliquefaction studies have been conducted in intraplate geologic settings, but a few such studies have been carried out in interplate settings. Paleoliquefaction studies provide information about timing, location, magnitude, and recurrence of large paleoearthquakes, particularly those with moment magnitude, M, greater than 6 during the past 50,000 years. This review paper presents background information on earthquake-induced liquefaction and resulting soft-sediment deformation features that may be preserved in the geologic record, best practices used in paleoliquefaction studies, and application of paleoliquefaction data in earthquake source characterization. The paper concludes with two examples of regional paleoliquefaction studies—in the Charleston seismic zone and the New Madrid seismic zone in the southeastern and central United States, respectively—which contributed to seismic source models used in earthquake hazard assessment.

SREDNEKEDROVAYA PALEOSEISMODISLOCATION IN THE BAIKAL RIDGE: ITS STRUCTURE AND THROWS ESTIMATED FROM GROUND‐PENETRATING RADAR DATA

Our study aimed to clarify the seismic potential of the Severobaikalsk fault and to discover the structural features of active faults on the NW shores of Lake Baikal. Seismogenic faults and large seismogravitational structures were mapped in the area of the Srednekedrovaya paleoseismodislocation, one of the most remarkable seismotectonic structures in the Baikal region. During the field trip, we tested the capacities of an OKO‐2 georadar and an ABDL‐ Triton antenna used to study cross‐sections of the Baikal ridge. Its slopes are steep, covered with Pinus pumila and abundant screes, many of which developed into boulder streams (‘kurumnik’). The first studies of the Sredneked‐ rovaya paleoseismodislocation were conducted by V.P. Solonenko and his team in 1964–1965. To some extent, this zone can be viewed as a reference object that can provide much information and thus deserves an in‐depth investiga‐ tion using new technologies. Our study combined the field observation and the interpretation of high‐resolution satel‐ lite images provided by DigitalGlobe (US) and downloaded by SAS.Planet. The consolidated database was sufficient for constructing a new schematic map showing the seismogenic faults associated with the Srednekedrovaya paleoseis‐ modislocation. The cumulative length of the ruptures observed on the surface amounted to almost 29.5 km. Some ruptures are separate from each other, and the rupture spacing ranges from the first tens of meters to the first kilome‐ ters. The width of the widest rupture zone is 1.9 km. The length of individual ruptures varies from 5.0 m to 2.7 km. Morphologically, the Srednekedrovaya paleoseismodislocation is represented by ledges and ditches that often comprise complex grabens disturbing the bedrock and slope deposits. The fault structure of this zone is a typical set‐ ting of orthogonal and slightly oblique crustal stretching, but its manifestation differs in the zone segments. In general, it is a combination of steeply dipping and listric faults traced to the depth of 13 m. In plan, the faults are observed to form the systems of subparallel ruptures that mainly strike at 30°. A linear relationship is established between the heights of the seismogenic ledges and the throws estimated from the ground‐penetrating radar data. The former are larger by 0.5–2.0 m than the throw measured from the radargrams. Apparently, this reflects the magnitude of expan‐ sion of the ledge upward along the sloping slope. In the zone of the main fault plane coinciding with the main ledge, the maximum and mean arithmetic throws are 8.3 and 4.93 m, respectively. On other fault planes, the throws range from 0.4 to 4.6 m. The paleoearthquake magnitude ranges from 6.8 to 7.6, according to the estimations from the seis‐ mic rock collapse volume, fault length, and the displacements. Our study of the Srednekedrovaya paleoseismodisloca‐ tion confirms that listric normal faulting is widespread along the western side of the North Baikal basin and gives in‐ direct evidence that conditions for accumulation and release of seismic energy are different on the western and east‐ ern shores of Lake Baikal. It should be noted, however, that in the studied near‐surface layer of the crust, the blocks of loose material may move along the flat planes due to gravitational sliding that increases under the impact of cryogenic processes on the steep slopes of the Baikal ridge.

Surface and shallow subsurface structure of the Middle Kedrovaya paleoseismic rupture zone in the Baikal Mountains from geomorphological and ground-penetrating radar investigations

The 30-km-long Middle Kedrovaya (MK) paleoseismic rupture zone, on the northwestern flank of Lake Baikal, is one of most impressive late Quaternary fault scarps in the Baikal rift. The aim of this study is to reconstruct the near-surface fault geometry of the MK fault zone to clarify its past movement history and seismic potential. We applied ground penetrating radar (GPR), along with high-resolution satellite imagery and field surface observations, to analyze the structure of the upper 12–13 m of the rupture zone and to characterize the complex structural environment in three dimensions. The GPR reveals that the shallow structure of the MK zone is defined by a combination of steep and listric normal faults, which form a surface pattern of subparallel ruptures trending predominantly N30°E. Individual surface scarps range from 5 m to 2.7 km in length and are separated by gaps of a few tens of meters to several kilometers apart. The greatest width of the scarp zone is 1.9 km. The vertical displacements measured independently from surface topographic profiles and from GPR radargrams are linearly related. The height of the main footwall (head) scarp is always 0.5–2 m greater than the throw measured on the radargrams, a result of the scarp face having broadened far up the talus slope after the latest displacement event. Maximum and average vertical normal fault displacements along the main fault trace, inferred from GPR data, are 8.3 and 4.98 m respectively. Paleoearthquake magnitude M estimated from empirical regressions ranges from 6.8 to 7.6, based on equations of M vs. surface rupture length, M vs. displacement, and M vs. landslide volume. Our study of the Middle Kedrovaya paleoseismic rupture zone confirms that listric normal faulting is widespread in the shallow (<13 m) subsurface of the western margin of the North Baikal basin. However, GPR data suggest that listric faulting is confined to the unconsolidated talus deposits and probably represents the effects of downhill gravitational sliding of the talus, and perhaps of underlying shallow bedrock. This downhill (lakeward) sliding of the hanging wall is partly responsible for the large heave component of movement on the MK rupture zone and its resulting unique geomorphic expression.This paper illustrates the practicality of investigating fault surface ruptures in complex environments by integrating data gathered by geophysics (GPR in this case) and by direct geomorphological observations. Because of the loose and mobile nature of the faulted talus deposit, the current surface morphology disguises the true number of subsurface faults, the lateral extent of faulting, and the unique structure types (all visible on radargrams) that developed to accommodate coseismic surface rupture with a large heave component.

Estimasi Magnitudo Paleoearthquake Dengan Metode Magnitude Bound

Yogyakarta was recorded unique seismic on the temple buildings such as Kedulan, Plaosan, Gampingan, Morangan and Kadisoka deformed on the body of the building due to liquefaction. Liquefaction structure found on the site of sand pillar, sand fissure and sand sill consisting of sand material that intrution other sediment layer. Magnitude Bound method is used to estimate the paleoearthquake magnitudes from paleoliquefaction data by utilizing the farthest distance liquefaction formed with epicenter earthquake. The application of the method shows that Yogyakarta had a large earthquake with magnitude of 6.25-6.5 M. The earthquake can cause severe physical damage, and can lead to secondary disasters such as liquefaction.

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.

Holocene activity evidence on the southeast boundary fault of Heqing basin, middle segment of Heqing-Eryuan fault zone, West Yunnan Province, China

The Heqing-Eryuan fault is an important part of the active fault system in the Northwestern Yunnan Province, China. Thus, the study on the nature, characteristics and activity history of this fault can provide not only the basis for seismic safety and engineering evaluation, but also the important information for the characteristics, history and patterns of the structural deformation of the southeastern margin of the Tibetan Plateau. Trench and faulted landforms investigations could provide effective paleoseismic methods to obtain the recent parameters of active faults. Using these methods, this study makes some breakthroughs on the recent activity of southeast boundary fault of the Heqing basin, middle segment of Heqing-Eryuan fault zone. Results indicate that the average vertical slip rate and left-lateral slip rate of the segment are about 0.28 mm/a and 1.80 mm/a respectively since the Late Pleistocene. The trench near the Beixi Village at the southeast boundary fault of the Heqing basin reveals that there have been at least three paleoearthquake events during the Holocene (~8 ka BP). The vertical displacement and sinistral strike-slip distance of a single paleoearthquake are ~20 cm and ~1.2 m, respectively. The estimated paleoearthquake magnitudes with Ms7.0, and the recurrence interval at 2-5 ka, as well as the latest activity time during 800- 290 cal yr BP, are of great significance for preventing and mitigating regional earthquake disasters.

Earthquake induced liquefaction features in the Karewas of Kashmir Valley North-West Himalayas, India: Implication to paleoseismicity

Earthquake induced liquefaction features found in the Karewas of Kashmir Valley are potential tools for estimating energy center, magnitude and peak ground acceleration of the paleoearthquakes. Size, pattern and spatial distribution of liquefaction features and in-situ geotechnical data were collected at the paleoliquefaction sites to assess the magnitude and peak ground acceleration of the paleoearthquake. The magnitude of paleoearthquakes was estimated to be of the order of (Mw = 6.2) using “Magnitude bound method” and “In-situ testing of geotechnical properties and assessment of liquefaction potential of liquefied beds (source stratum) using cyclic stress method”. The peak ground acceleration computed were in the range of 0.27g to 0.83g using cyclic stress method and 0.30g using attenuation equation NDMA [21].

Variability in magnitude of paleoearthquakes revealed by trenching and historical records, along the Haiyuan Fault, China

AbstractPaleoseismology provides fundamental data for generalizing earthquake recurrence behavior, by revealing past surface‐rupturing events. Determining the size of paleoseismic events is notoriously more challenging than their timing. Paleoearthquakes exposed in trenches are vaguely defined as large enough to break to the surface and often assumed to be similar in size. Here we show an example where the paleoseismic record includes events of both moderate and large magnitudes. At the Salt Lake site on the active left‐lateral Haiyuan Fault, northern Tibetan Plateau, a high‐resolution stratigraphic sequence recorded three and possibly four events since A.D. 1500, constrained by accelerator mass spectrometry14C dating. Historical accounts of earthquake damage in the study region suggest that several earthquakes exposed in the trenches markedly differ in magnitude. With the exception of the most recentM~8 earthquake that occurred in A.D. 1920, two earlier events, which occurred in A.D. 1760 (or 1709) and 1638, respectively, are considerably smaller, with magnitudeM &lt; 7 and more likelyM~6 or less. Thus, this section of the Haiyuan Fault that broke during moderate‐magnitude events failed again after a short interval during a largeMw7.8–8.3 earthquake, as part of a larger multisegment rupture. Our study shows that moderate‐magnitude events can be preserved in the stratigraphy and exposed by paleoseismic trenching under ideal conditions, for instance, if sedimentation is fast enough and there is no hiatus in deposition. Eventually, the data presented add to the growing body of paleoseismic records containing events of different magnitudes with a large variability in rupture length and coseismic slip.

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.

SEISMOGRAVITATIONAL PALEODISLOCATIONS IN THE CHAGAN RIVER VALLEY (SOUTH-EASTERN ALTAI)

The investigation of large landslides and rock-falls in Chagan-river valley along with the seismic microdeforma-tions of glacial sediments in Chagan section prove seismic activity of SE Altai in the Pleistocene-Holocene. Magnitude of paleoearthquake which caused the largest landslide in the left wall of Chagan-river valley is estimated together with the total volume of material displaced in this part of the valley by the whole Holocene seismic activity.

Soft-sediment deformation structures in the Cretaceous Zhucheng depression, Shandong Province, East China; their character, deformation timing and tectonic implications

Various plastic and brittle soft-sediment deformation structures (SSDS) are recognized in Cretaceous sedimentary rocks of the Zhucheng depression, East China record important information on the different sediment characteristics, depositional settings and tectonic movements involved in their formation. The recognized SSDS include undulate folds, mound-and-sag structures, diapirs, convolute features and a seismically induced unconformity. The Lower Cretaceous sedimentary rocks are fine grained, lacustrine deposits, whereas those of the Upper Cretaceous are coarse-grained sandstones and conglomerates formed in an alluvial fan or flood-plain setting. These SSDS with coarse-grained rocks are characterized by fault grading, load cast structures, ball and pillow structures and plunged sediment mixture structures. We propose that the SSDS was triggered by paleo-earthquakes. Alternating deformed and undeformed layers suggest frequent and repeated seismic activity. Stratigraphic correlations, the evaluation of magmatic events and the youngest detrital zircon ages indicate that the deformational events occurred mainly in the Early Cretaceous between 118Ma to 105Ma, and in the Late Cretaceous at approximately 100Ma. Numerous giant hadrosaurid fossil skeletons have been found in the Upper Cretaceous Wangshi Group, and unusual and abundant dinosaur tracks are preserved in the Lower Cretaceous Yangzhuang Formation of the Laiyang Group. The zones of widespread SSDS closely underlie and overlie the dinosaur fossil-bearing strata. The depositional setting changed in response to multiple paleoseismic events and regional tectonic movements. After many paleoearthquakes and environmental changes in the Early Cretaceous, many dinosaurs appear to have migrated, based on the presence of many tracks with a similar orientation in lacustrine sedimentary rocks. In the Late Cretaceous strata, large-scale dinosaur fossil layers are associated with paleo-earthquake records, suggesting that the dinosaur fossil burial may be associated with large-scale debris flows triggered by frequent earthquakes. Based on regional tectonic setting, the distribution of SSDS and the predicted paleo-earthquake magnitudes, the seismogenic fault may have been the Wulian Fault.