Prehistoric Earthquakes Research Articles

Reconstructing paleoseismic deformation, 2: 1000 years of great earthquakes at Chucalén, south central Chile

In this paper we adopt a quantitative biostratigraphic approach to establish a 1000-year-long coastal record of megathrust earthquake and tsunami occurrence in south central Chile. Our investigations focus on a site in the centre of the rupture segment of the largest instrumentally recorded earthquake, the AD 1960 magnitude 9.5 Chile earthquake. At Chucalén coseismic subsidence in 1960 is recorded in the lithostratigraphy and biostratigraphy of coastal marshes, with peat overlain by minerogenic sediment and changes in the assemblages of diatoms (unicellular algae) indicating an abrupt increase in relative sea level. In addition to the 1960 earthquake, the stratigraphy at Chucalén records three earlier earthquakes, the historically documented earthquake of 1575 and two prehistoric earthquakes, radiocarbon dated to AD 1270–1450 and 1070–1220. Laterally extensive sand sheets containing marine or brackish diatom assemblages suggest tsunami deposition associated with at least two of the three pre-1960 earthquakes. The record presented here suggests a longer earthquake recurrence interval, averaging 270 years, than the historical recurrence interval, which averages 128 years. The lack of geologic evidence at Chucalén of two historically documented earthquakes, in 1737 and 1837, supports the previously suggested hypothesis of variability in historical earthquake characteristics. Our estimates of coseismic land-level change for the four earthquakes range from meter-scale subsidence to no subsidence or slight uplift, suggesting earthquakes completing each ∼270 year cycle may not share a common, characteristic slip distribution. The presence of buried soils at elevations below their modern equivalents implies net relative sea-level rise over the course of the Chucalén paleoseismic record, in contrast to relative sea-level fall over preceding millennia inferred from sites on the mainland. Sea-level rise may contribute to the preservation of evidence for multiple earthquakes during the last millennium, while net relative sea-level fall over the last 2000–5000 years may explain the lack of evidence for older earthquakes.

Late Holocene Slip Rate and Ages of Prehistoric Earthquakes along the Maacama Fault Near Willits, Mendocino County, Northern California

Abstract The Maacama fault is the northward continuation of the Hayward–Rodgers Creek fault system and creeps at a rate of 5.7±0.1 mm/yr (averaged over the last 20 years) in Willits, California. Our paleoseismic studies at Haehl Creek suggest that the Maacama fault has produced infrequent large earthquakes in addition to creep. Fault terminations observed in several excavations provide evidence that a prehistoric surface‐rupturing earthquake occurred between 1060 and 1180 calibrated years (cal) B.P. at the Haehl Creek site. A folding event, which we attribute to a more recent large earthquake, occurred between 790 and 1060 cal B.P. In the last 560–690 years, a buried channel deposit has been offset 4.6±0.2 m, giving an average slip rate of 6.4–8.6 mm/yr, which is higher than the creep rate over the last 20 years. The difference between this slip rate and the creep rate suggests that coseismic slip up to 1.7 m could have occurred after the formation of the channel deposit and could be due to a paleoearthquake known from paleoseismic studies in the Ukiah Valley, about 25 km to the southeast. Therefore, we infer that at least two, and possibly three, large earthquakes have occurred at the Haehl Creek site since 1180 cal B.P. (770 C.E.), consistent with earlier studies suggesting infrequent, large earthquakes on the Maacama fault. The short‐term geodetic slip rate across the Maacama fault zone is approximately twice the slip rate that we have documented at the Haehl Creek site, which is averaged over the last approximately 600 years. If the geodetic rate represents the long‐term slip accumulation across the fault zone, then we infer that, in the last ∼1200 years, additional earthquakes may have occurred either on the Haehl Creek segment of the Maacama fault or on other active faults within the Maacama fault zone at this latitude. Online Material: Trench logs, discussion of channel B, photographs of compressional features, and table of radiocarbon analyses.

Estimating magnitudes of prehistoric earthquakes and seismic capability of fault from landslide data in Noor valley (central Alborz, Iran)

Detecting the paleoseismological specifications as well as seismic capability of faults has specific importance in estimating the earthquake hazard in any region. The geomorphic indices are used as indirect procedures in the mountainous area. They are appropriate and applicable methods in recognizing the specifications of active tectonics and evaluating fault seismicity in the mountainous areas. In this regard, giant landslides can be pointed out as proper indices. These landslides are usually related to tectonics and triggered by earthquakes in many cases. In this research, giant landslides existed in Noor valley (central Alborz) have been considered as geomorphological indices for recognizing the seismicity of the region and the seismic capability of its faults. There are four giant landslides in this region (Baladeh, Razan, Vakamar, and Iva) used for the mentioned purpose. No historical earthquake has been reported around Noor valley. However, the existence of giant and old landslides, related to earthquake, indicates the occurrence of numerous prehistoric earthquakes. In this research, three different age classes have been determined (Late Holocene, Early Holocene, and Late Pleistocene) for landslides. By the way, the possibility of identifying multiple earthquakes is provided in this area. The magnitudes of earthquakes are estimated as 7.7 ± 0.49 to 7.9 ± 0.49 based on their relations with maximum volume of displaced material. Regarding the distribution of landslides and other evidences, the eastern segment of Baladeh fault has probably been the main cause of the earthquakes.

Submarine paleoseismology of the northern Hikurangi subduction margin of New Zealand as deduced from Turbidite record since 16 ka

Paleoseismic studies seek to characterise the signature of pre-historical earthquakes by deriving quantitative information from the geological record such as the source, magnitude and recurrence of moderate to large earthquakes. In this study, we provide a ∼16,000 yr-long paleo-earthquake record of the 200 km-long northern Hikurangi Margin, New Zealand, using cm-thick deep-sea turbidites identified in sediment cores. Cores were collected in strategic locations across the margin within three distinct morphological re-entrants – the Poverty, Ruatoria and Matakaoa re-entrants. The turbidite facies vary from muddy to sandy with evidence for rare hyperpycnites interbedded with hemipelagites and tephra. We use the Oxal probabilistic software to model the age of each turbidite, using the sedimentation rate of hemipelagite deduced from well-dated tephra layers and radiocarbon ages measurements on planktonic foraminifera.Turbidites are correlated from one core to the other using similarity in sedimentary facies, petrophysical properties and ages. Results show that 46 turbidites are synchronous along the entire margin. Amongst them 41 are interpreted as originating from the upper continental slope in response to earthquake-triggered slope failures between 390 ± 170 to 16,450 ± 310 yr BP. Using well-established empirical relationships that combine peak ground acceleration, magnitude and location of earthquakes, we calculate that synchronous slope failures were triggered by the rupture of 3 of the 26 known active faults in the region, each capable of generating Mw 7.3 to 8.4 earthquakes – two are crustal reverse faults and one is the subduction interface. The 41 Mw ≥ 7.3 earthquakes occurred at an average recurrence interval of ∼400 yr over the last ∼16,000 yr. Among them, twenty are interpreted as subduction interface earthquakes that occurred at an average recurrence interval of ∼800 yr, with alternating periods of high activity and low return times (305–610 yr) and quiescence periods with high return times (1480–2650 yr). Based on turbidite paleoseismology, we propose that subduction interface earthquakes were of lower magnitude during active periods (Mw > 7.5) than during quiescence periods (Mw ≥ 8.2).

Comparison of seismotectonic peculiarities of Altai Mountains and Mongolian Altai

The paleoseismogeological studies within the two representative segments of fold systems in the Altai mobile belt (Altai Mountains and Mongolian Altai) have been carried out. These studies revealed the primary seismodislocations (seismic ruptures) of both the ancient historic and prehistoric strongest earthquakes. Based on amplitudes of single displacements (reverse fault and normal fault motions were 0.5–1.6 m) and with the significant strike slip component (more than 1.5 m) taken into account, the magnitude of ancient events in the Altai Mountains was determined at approximately 7.5. The recurrence period is 1400 years on average for the M = 7.0 events and 2100 years for the M = 7.5 ones. In the western Mongolian Altai, reverse fault motions were up to 2 m, corresponding to an earthquake magnitude of about 8.0 (an analog with the 1931 Fuyun earthquake). The recurrence period for the strongest earthquakes in Mongolian Altai was longer than that for the Altai Mountains, about 3000 years. This can be explained by higher magnitude values for western Mongolian Altai. It also can be concluded that the seismic regimes of the Altai Mountains and Mongolian Altai remained almost unchanged during the entire Holocene.

Glacier dynamics, palaeohydrological changes and seismicity in southeastern Altai (Russia) and their influence on human occupation during the last 3000 years

The 3 ka chronology of climatically driven glacier fluctuations and upper tree limit variations, dates of strong prehistoric earthquakes, and fluvial system transformation are established for the SE Altai (mountains of South Siberia) on the basis of radiocarbon and dendrochronological dating. This time period of prosperity of the Altai nomadic cultures is characterized by more arid and cold climate in comparison with the first half of the Holocene. During the last 3 ka, glacier advances occurred at 2300–1700 cal. BP (Historical stage) and 13th–19th centuries (Aktru stage (LIA)). The recurrence interval of strong prehistoric earthquakes is estimated as ∼400 years. The final draining of the Holocene lake in the Chuya intermountain depression took place about 1500 cal. BP. All these natural events together with political and social factors controlled the nomadic population, their habitat, and the patterns of evolution and migration of nomadic cultures within the SE Altai. Aridity intensification and cooling enhanced by anthropogenic impact brought deforestation of the eastern part of the Chuya depression.

Heterogeneous rupture in the great Cascadia earthquake of 1700 inferred from coastal subsidence estimates

AbstractPast earthquake rupture models used to explain paleoseismic estimates of coastal subsidence during the great A.D. 1700 Cascadia earthquake have assumed a uniform slip distribution along the megathrust. Here we infer heterogeneous slip for the Cascadia margin in A.D. 1700 that is analogous to slip distributions during instrumentally recorded great subduction earthquakes worldwide. The assumption of uniform distribution in previous rupture models was due partly to the large uncertainties of then available paleoseismic data used to constrain the models. In this work, we use more precise estimates of subsidence in 1700 from detailed tidal microfossil studies. We develop a 3‐D elastic dislocation model that allows the slip to vary both along strike and in the dip direction. Despite uncertainties in the updip and downdip slip extensions, the more precise subsidence estimates are best explained by a model with along‐strike slip heterogeneity, with multiple patches of high‐moment release separated by areas of low‐moment release. For example, in A.D. 1700, there was very little slip near Alsea Bay, Oregon (~44.4°N), an area that coincides with a segment boundary previously suggested on the basis of gravity anomalies. A probable subducting seamount in this area may be responsible for impeding rupture during great earthquakes. Our results highlight the need for more precise, high‐quality estimates of subsidence or uplift during prehistoric earthquakes from the coasts of southern British Columbia, northern Washington (north of 47°N), southernmost Oregon, and northern California (south of 43°N), where slip distributions of prehistoric earthquakes are poorly constrained.

Historical tsunami deposits in Peru: Sedimentology, inverse modeling and optically stimulated luminescence dating

The entire coast of Perú was surveyed to document deposits of historical tsunami. Evidence of four tsunami was found. At Puerto Casma, in northern Perú, a graded, heavy mineral-rich layer with shell- and rock fragments was detected. OSL dating revealed an age of 0.37 ± 0.03 ka (1615–1667 AD). Inverse modelling of tsunami onshore flow parameters indicates a flow depth of ∼6 m and a flow speed of ∼8 m/s at a distance of ∼60 m from the shoreline. For the Chimbote earthquake of 1619 AD, a tsunami was not listed in the historical tsunami catalogues, although it is seen as a predecessor of the 1996 Chimbote earthquake and tsunami. Hence, this study may provide the first evidence of a local tsunami triggered by this event. A graded, shell-rich event layer that contains cobbles with attached marine organisms was found at Vila Vila in southern Perú. This layer was dated to 0.17 ± 0.04 ka (1797–1871 AD) and is most probably the result of the 1868 Arica tsunami. Two additional event layers found in Boca del Río (southern Perú) were dated 2.26 ± 0.37 ka (615 BC–119 AD) and 1.98 ± 0.23 ka (207 BC–255 AD). Thus, the layers record for the first time tsunami much older than the events listed in tsunami catalogues. These two events exhibit similar parameters with flow speeds of 7–8 m/s and depths of 6 m in a distance of 460 m from the present shoreline. The time that passed between the events is similar to the recurrence interval of the two Arica tsunami of 1604 and 1868 AD, hence giving evidence of another prehistoric earthquake and tsunami couplet.

Arshan palaeoseismic feature of the Tunka fault (Baikal rift zone, Russia)

The traditional concept of the rift development of flank depressions in the Baikal rift zone is now doubted in view of some indicators for compression deformations identified by the seismogeological and geodetic methods. Besides, the paleoseismological investigations revealed seismogenic strike-slips and reverse faults in the Tunka fault zone that is a major structure-controlling element of the Tunka rift depression. However, a detailed study of the upslope-facing scarp in the Arshan paleoseismogenic structure zone has shown that its formation might be due to rift mechanism of basin formation. Age estimation has been made for the previously unknown pre-historic earthquake whose epicentral area coincides with the western flank of the Arshan paleoseismogenic structure. Judging from previously determined ages of paleoearthquakes, the mean recurrence period for faulting events on the central Tunka fault is 2780–3440years.

Paleoseismic studies and the long-term seismic regime in the North of Sakhalin Island

Collected and systematized materials for the ancient seismic shocks in the northern part of Sakhalin Island, in the areas of Upper Piltun, Garomai, Piltun, and Kheiton active faults, have allowed us to reconstruct the history of occurrence of strong earthquakes for almost the entire Holocene. Traces of previously unknown prehistoric earthquakes with magnitudes 6.0, 7.0, 7.5 and 8.0 are detected, time of recurrence based on data trenching are estimated. All these new paleoseismic data covering almost the entire Holocene are the basis for long-term of the seismic regime reconstruction of northern Sakhalin. For plotting the schedule of the earthquake recurrence in northern Sakhalin, instrumental, historical and paleoseismic data are used. The results indicate that seismic regime during the Holocene stage of regional evolution was stable. There is a high degree of correlation between instrumental, historical and paleoseismological data used to plot the frequency of occurrence.

Neotectonics and paleoseismicity of the lower Katun’ valley (Gorny Altai)

The lower Katun’ area has a complex neotectonic framework, with the largest fault zone of Katun’ consisting of several en-echelon graben segments. Late Pleistocene sediments that fill the Katun’ Fault bear signature of earthquake-induced soft-sediment deformation (seismites). Deformation due to seismic triggers can be discriminated from nonseismic one on the basis of special features and be related to prehistoric earthquakes according to a number of criteria. The observed deformation inside and outside burial mounds of the Chultukov Log-1 group may result from an earthquake that occurred in the end of the first millennium BC. Fault scarps in Late Pleistocene sediments, as well as deformed Iron Age tomb patterns, indicate that the Katun’ lower reaches can have experienced past earthquakes of intensity at least 5 or 6 and magnitudes from 4.5 to 6.0.

Mineral, Virginia, earthquake illustrates seismicity of a passive‐aggressive margin

The August 2011 M 5.8 Mineral, Virginia, earthquake that shook much of the northeastern U.S. dramatically demonstrated that passive continental margins sometimes have large earthquakes. We illustrate some general aspects of such earthquakes and outline some of the many unresolved questions about them. They occur both offshore and onshore, reaching magnitude 7, and are thought to reflect reactivation of favorably‐oriented, generally margin‐parallel, faults created during one or more Wilson cycles by the modern stress field. They pose both tsunami and shaking hazards. However, their specific geologic setting and causes are unclear because large magnitude events occur infrequently, microseismicity is not well recorded, and there is little, if any, surface expression of repeated ruptures. Thus presently active seismic zones may be areas associated with higher seismicity over the long term, the present loci of activity that migrates, or aftershock zones of large prehistoric earthquakes. The stresses causing the earthquakes may result from platewide driving forces, glacial isostatic adjustment, localized margin stresses, and/or dynamic topography. The resulting uncertainties make developing cost‐effective mitigation strategies a major challenge. Progress on these issues requires integrating seismic, geodetic, and geological techniques.

Evidencias ambientales de cambios de nivel de la costa del Pacífico de México: terremotos y tsunamis

The study of prehistoric earthquakes and tsunamis using environmental evidence of coastal level changes, where sudden changes from terrestrial to marine environments, and vice versa, and where tsunami deposits are preserved, has provided valuable information in the earthquake and tsunami hazard assessment. The Pacific coast of Mexico is tectonically active and has experienced numerous large magnitude earthquakes (M > 7.5) in historical times, frequently accompanied by coastal-level changes and tsunamis (> 50 tsunamis recorded since 1732). Using the case study of tropical lagoons and marshes on the Guerrero coast, it is shown the feasibility of recording tectonically induced coastal level changes through the proxy method that integrates geomorphic, stratigraphic, geochemical, microfossil, and radiometric data. The applied method confirms evidence for environmental changes indicative of coastal subsidence and a potential great earthquake and tsunami by ca. 3400-3500 yr BP. In general, most of the Holocene relative sea-level changes observed obscure any climatic signal in this period on the Mexican Pacific coast

Probabilistic Seismic-Hazard Assessment Including Site Effects for Evansville, Indiana, and the Surrounding Region

Abstract Evansville, Indiana, is one of the closest large urban areas to both the New Madrid Seismic Zone, where large earthquakes occurred in 1811–1812, and the Wabash Valley Seismic Zone, where there is evidence of several large prehistoric earthquakes in the last 14,000 yr. For this reason, Evansville has been targeted as a priority region for urban seismic-hazard assessment. The probabilistic seismic-hazard methodology used for the Evansville region incorporates new information from recent surficial geologic mapping efforts, as well as information on the depth and properties of near-surface soils and their associated uncertainties. The probabilistic seismic-hazard calculation applied here follows the method used for the 2008 United States Geological Survey (USGS) national seismic-hazard maps, with modifications to incorporate estimates of local site conditions and their uncertainties, in a completely probabilistic manner. The resulting analysis shows strong local variations of acceleration with 2% probability of exceedance in 50 yr, which are clearly correlated with variations in the thickness of unconsolidated soils above bedrock. Spectral accelerations at 0.2-s period range from 0.6 to 1.5 g , values that are much greater than those of the USGS national seismic-hazard map, which assume B/C site conditions with an average shear-wave velocity of 760 m/s in the top 30 m. The presence of an ancient bedrock valley underlying the current Ohio River flood plain strongly affects the spatial pattern of accelerations. For 1.0-s spectral acceleration, ground motions are significantly amplified due to deeper soils within this structure, to a level comparable to that predicted by the national seismic-hazard maps with D site conditions assumed. For PGA and 0.2-s spectral acceleration, ground motions are significantly amplified outside this structure, above the levels predicted by the national seismic-hazard maps with uniform D site conditions assumed.

Complex rupture during the 12 January 2010 Haiti earthquake

Initially, the devastating Mw 7.0, 12 January 2010 Haiti earthquake seemed to involve straightforward accommodation of oblique relative motion between the Caribbean and North American plates along the Enriquillo‐Plantain Garden fault zone. Here, we combine seismological observations, geologic field data and space geodetic measurements to show that, instead, the rupture process involved slip on multiple faults. Primary surface deformation was driven by rupture on blind thrust faults with only minor, deep, lateral slip along or near the main Enriquillo‐Plantain Garden fault zone; thus the event only partially relieved centuries of accumulated left-lateral strain on a small part of the plate-boundary system. Together with the predominance of shallow off-fault thrusting, the lack of surface deformation implies that remaining shallow shear strain will be released in future surface-rupturing earthquakes on the Enriquillo‐Plantain Garden fault zone, as occurred in inferred Holocene and probable historic events. We suggest that the geological signature of this earthquake—broad warping and coastal deformation rather than surface rupture along the main fault zone—will not be easily recognized by standard palaeoseismic studies. We conclude that similarly complex earthquakes in tectonic environments that accommodate both translation and convergence—such as the San Andreas fault through the Transverse Ranges of California—may be missing from the prehistoric earthquake record.

Paleoseismogeological Investigations in a “Seismic Gap” in the Northwest Caucasus Compared to the West Himalayan Region

In this article we have compared the results of seismotectonic and paleoseismogeologic investigations for representative segments of the two fold systems of the Alpine-Himalayan mobile belt (in the North- west Caucasus and West Himalayas). It has been found that during the previously identified “seismic gaps,” in both cases, we are dealing with primary dislocations (seismic ruptures) of ancient historical and prehistoric strong earthquakes. According to estimations, the magnitude of one-act seismogenic displacements in the first region was about 6.5-7.0 m, and the recurrence period ranges from 500 to 1500 years on average. In the West Himalayas, the overthrust displacements along the ruptures were 6-7 m, which corresponds to an 8.0-magnitude earthquake. At the same time, the recurrence period of strong earthquakes during a seismic gap in the Himalayas was 500-1000 years, which is similar to that in the Caucasus. The data collected also demonstrate the correct preliminary estimation of the seismic potential of zones of seismic quiescence in both the studied fold systems.

Evidence of large prehistoric offshore earthquakes deduced from uplifted Holocene marine terraces in Pangasinan Province, Luzon Island, Philippines

Uplifted Holocene marine terraces in Pangasinan Province, westernmost Luzon Island, Philippines are reported here for the first time as geomorphic evidence of large prehistoric offshore earthquakes. We recognized up to three Holocene terrace steps. Elevations of shoreline angles are TI: 1 to 5 m, TII: 2 to 7 m, and TIII: 4 to 11 m above mean sea level (amsl). The lateral variation in the elevation of terrace steps indicates differential uplift along the coast. The staircase topography, characterized by horizontal abrasion platforms, meter-scale terrace risers, and wave-cut notches, suggests that these geomorphic features were formed by large coseismic uplift events. Terrace morphology and radiocarbon ages further suggest that at least three coseismic coastal uplift events have occurred since the culmination of the post-glacial sea level rise ~ 6000 years ago. We interpret TIII to be the Holocene transgressive surface (~ 6000 yBP) and estimated a maximum uplift rate of 1.7 mm/yr which is almost the same as the Late Pleistocene uplift rate of 1.3 mm/yr. We infer that proximity to offshore seismic sources has contributed to the deformation pattern of Holocene terraces and variation in the number of terrace steps. Uplift patterns of marine terraces also suggest that the magnitude and location of prehistoric earthquakes may have varied between individual coseismic uplift events. We conducted simple elastic dislocation modeling to evaluate the source parameters of the causative faults. Our preliminary models show that a landward-dipping offshore reverse fault located at the base of a steep slope separating the fore arc basin and continental shelf could be responsible for coastal uplift along the western Pangasinan peninsula.

Century-long average time intervals between earthquake ruptures of the San Andreas fault in the Carrizo Plain, California

Paleoseismological data constrain the age, location, and associated magnitude of past surface-rupturing earthquakes; these are critical parameters for developing and testing fault behavior models and characterizing seismic hazard. We present new earthquake evidence and radiocarbon analyses that refi ne the chronology of the six most recent earthquakes that ruptured the south-central San Andreas fault in the Carrizo Plain (California, United States) at the Bidart Fan site. Modeled 95 percentile ranges of the earthquakes prior to the A.D. 1857 earthquake are A.D. 1631‐1823, 1580‐1640, 1510‐1612, 1450‐1475, and 1360‐1452. The average time interval between the last six earthquakes that ruptured the San Andreas fault in the Carrizo Plain is 88 ± 41 yr. This is less than the time since the most recent A.D. 1857 earthquake, less than all reported average intervals of prehistoric earthquakes along the entire San Andreas fault, and signifi cantly shorter than the 235 yr average used in recent seismic hazard evaluations. The new chronological data combined with recent slip studies imply that the magnitudes of the earthquakes that ruptured the southern San Andreas fault in the Carrizo Plain since ca. A.D. 1360 were variable, and suggest that the widely held view of rare but great surface rupturing earthquakes along this portion of the southern San Andreas fault should be reevaluated. 118°

Prehistoric earthquakes on the Caribbean–South American plate boundary, Central Range fault, Trinidad

Research Article| August 01, 2010 Prehistoric earthquakes on the Caribbean–South American plate boundary, Central Range fault, Trinidad Carol S. Prentice; Carol S. Prentice 1U.S. Geological Survey, 345 Middlefield Road, MS 977, Menlo Park, California 94025, USA Search for other works by this author on: GSW Google Scholar John C. Weber; John C. Weber 2Department of Geology, Grand Valley State University, Allendale, Michigan 49401, USA Search for other works by this author on: GSW Google Scholar Christopher J. Crosby; Christopher J. Crosby 1U.S. Geological Survey, 345 Middlefield Road, MS 977, Menlo Park, California 94025, USA *Current address: San Diego Supercomputer Center, University of California–San Diego, MC 0505, 9500 Gilman Drive, La Jolla, California 92093-0505, USA Search for other works by this author on: GSW Google Scholar Daniel Ragona Daniel Ragona 3Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California–San Diego, La Jolla, California 92121, USA †Current address: BP America, 501 Westlake Park Blvd., Houston, Texas 77079, USA Search for other works by this author on: GSW Google Scholar Geology (2010) 38 (8): 675–678. https://doi.org/10.1130/G30927.1 Article history received: 02 Dec 2009 rev-recd: 19 Feb 2010 accepted: 21 Feb 2010 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Carol S. Prentice, John C. Weber, Christopher J. Crosby, Daniel Ragona; Prehistoric earthquakes on the Caribbean–South American plate boundary, Central Range fault, Trinidad. Geology 2010;; 38 (8): 675–678. doi: https://doi.org/10.1130/G30927.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Recent geodetic studies suggest that the Central Range fault is the principal plate-boundary structure accommodating strike-slip motion between the Caribbean and South American plates. Our study shows that the fault forms a topographically prominent lineament in central Trinidad. Results from a paleoseismic investigation at a site where Holocene sediments have been deposited across the Central Range fault indicate that it ruptured the ground surface most recently between 2710 and 550 yr B.P. If the geodetic slip rate of 9–15 mm/yr is representative of Holocene slip rates, our paleoseismic data suggest that at least 4.9 m of potential slip may have accumulated on the fault and could be released during a future large earthquake (M > 7). You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

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.