Paleoseismic Analysis Research Articles

Late Holocene earthquakes in southern Apennine: paleoseismology of the Caggiano fault

Although southern Apennines are characterized by the strongest crustal earthquakes of central-western Mediterranean region, local active tectonics is still poorly known, at least for seismogenic fault-recognition is concerned. Research carried out in the Maddalena Mts. (southeast of Irpinia, the region struck by the Mw=6.9, 1980 earthquake) indicates historical ruptures along a 17-km-long, N120° normal fault system (Caggiano fault). The system is characterized by a bedrock fault scarp carved in carbonate rocks, which continues laterally into a retreating and eroded smoothed scarp, affecting the clayey-siliciclastic units, and by smart scarps and discontinuous free-faces in Holocene cemented slope-debris and in modern alluvial fan deposits. The geometry of the structure in depth has been depicted by means of electrical resistivity tomography, while paleoseismic analysis carried out in three trenches revealed surface-faulting events during the past 7 ky BP (14C age), the latest occurred in the past 2 ky BP (14C age) and, probably, during/after slope-debris deposition related to the little ice age (∼1400–1800 a.d.). Preliminary evaluation accounts for minimum slip rates of 0.3–0.4 mm/year, which is the same order of rates estimated for many active faults along the Apennine chain. Associated earthquakes might be in the order of Mw=6.6, to be compared to the historical events occurred in the area (e.g., 1561 and 1857 p.p. earthquakes).

Disruptive earthquakes revealed by faulted archaeological relics in Samnium (Molise, southern Italy)

Archaeoseismic and paleoseismic analyses carried out along the northern slope of the Matese massif (Samnium, southern Apennines) revealed cumulative offsets affecting the walls of the Hercules's sanctuary of Campochiaro (4th cent. BC‐5th cent. AD) and its foundation deposits. On the basis of the archaeological data, a first faulting event (unknown in historical sources and seismic catalogues) occurred during the 3rd cent. BC, followed by other displacements which are consistent with the catastrophic 1456 and 1805 earthquakes. The sanctuary is located close to one of the E‐W strands of the northern‐Matese fault system (NW‐SE trending), to which we relate the observed deformation. Our data suggest that the activity of this fault system is characterized by high slip‐rates (0.9 mm/yr) if compared to other known active faults in the Apennines, and irregular return time for earthquakes with M > 6.5.

Magnitudes of Prehistoric Earthquakes in the South Carolina Coastal Plain from Geotechnical Data

In-situ geotechnical data were collected near paleoliquefaction features in the South Carolina Coastal Plain (SCCP) to assess the magnitudes and peak ground accelerations of prehistoric earthquakes. Currently used paleoseismic analysis methods were used to back-calculate the magnitudes of prehistoric earthquakes and peak ground accelerations that can cause paleoliquefaction features in the SCCP. The results from multiple methods yielded similar results and indicated that the prehistoric earthquakes in the SCCP that occurred during the past 6,000 years and caused paleoliquefaction features have magnitudes ranging from 5.3 to 7.8. The peak ground accelerations needed to cause liquefaction are also consistent among the different methods and ranged between about 0.1 and 0.3 g for M 7.5 and between about 0.1 and 0.5 g for M 6.0 earthquakes. These results were used together with those of earlier paleoseismological investigations to estimate the magnitudes and peak ground accelerations associated with prehistoric earthquake episodes. For earthquake episodes centered at Charleston, the estimated magnitudes and peak ground accelerations range from 6.8 to 7.8 and 0.16 to 0.24 g, respectively. For episodes centered near Georgetown, the estimated magnitudes and peak ground accelerations range from 5.5 to 7.0 and 0.21 to 0.42 g, respectively.

New empirical relationships between magnitude and distance for liquefaction

Historical research performed in the 1990s has updated previous compilations of liquefaction-induced phenomena that occurred during the last millenium in Italy. Liquefaction indications are reported in Italy for earthquakes with I o>5–6 (MCS) and M s≥4.2, 90% of the cases falling within 50 km of the epicenter. The recently re-evaluated seismic parameters of the Italian historical earthquakes, together with the location of 317 indications of liquefaction features, provide a relatively complete database, permitting the author to highlight the distribution of intensity/magnitude values versus epicentral distance. In paleoseismic analyses these relationships may be considered a tool in evaluating the minimum energy of an earthquake that induced liquefaction features.

Active faulting and paleoseismology along the Bree fault, lower Rhine graben, Belgium

Paleoseismic analysis of the 10‐km‐long Bree fault scarp in the lower Rhine graben yields numerous lines of evidence of earthquake activity in the Holocene and late Pleistocene. This active normal fault, a part of the Feldbiss fault system, dips 70°NE and is expressed at the surface by a prominent NW‐SE trending 7 to 20 m high scarp, formed since the deposition of the Maas River main terrace <700 kyr. B.P. Trenches and geophysical prospecting show that the fault, which is known to have ∼100 m of vertical offset since the late Pliocene, breaks late Pleistocene and Holocene deposits. Ground‐penetrating radar, seismic refraction, and electric tomography suggest that at shallow depth the amount of displacement is larger than the youngest vertical offset visible in the trenches and corresponds to cumulative fault displacements. The analysis of 36 leveling profiles across the scarp indicates that its height can be classified into three groups, likely corresponding to different events. A morphologic dating gives approximate ages of 2±1.5 kyr B.P., 14±5 kyr B.P., and 41±6 kyr B.P. for the past three surface‐faulting earthquakes. Analysis of faulted stratigraphy and earthquake‐induced deformation structures exposed in trenches suggests the occurrence of three large earthquakes during the past 45×l03 years and yields 0.07 mm/yr of relative vertical deformation rate. The most recent seismic event occurred between A.D. 610 and 890. The first identification of an active fault with surface ruptures in the lower Rhine graben area emphasizes that large earthquake sources exist within intraplate Europe and that at least some of these events are preserved in the geologic record.

Changes in Holocene Paleoseismic activity in the Hula pull-apart basin, Dead Sea Rift, northern Israel

Paleoseismic analysis of the Azaz fault segment of the Dead Sea Fault (northern Israel), indicates that this region was subjected to intermittent periods of strong seismicity and quiescence during the latest Pleistocene and the Holocene. The Azaz fault forms the eastern margin of the Hula Valley, a pull-apart basin between two left-stepping segments of the Dead Sea Fault. The fault is currently inactive, but it displaces a 25–30 ka travertine in the northeastern corner of the Hula Valley and near-surface marsh sediments inside the valley. Two trenches excavated across a 15–20 m high fault scarp near Kefar Szold expose fluvial and colluvial sequences showing clear evidence of recent tectonics. One trench exposes well sorted, bedded alluvial sediments comprising two upward-fining units, each capped by a weakly developed paleosol. The sediments were deposited on the down-faulted block and are bounded in the east by the fault scarp. The second trench uncovers fine colluvial sediments cross-cut by a wide fault-parallel fissure filled by collapsed sediments. In both trenches, the lower sedimentary unit is capped by a coarse colluvium containing boulders up to 1.5 m in size. The colluvium shows no clear bedding and has a weakly developed paleosol on top. Optically stimulated luminescence dating of the lower fluvial sequence shows that its age ranges between 12 ka at the base to 6 ka at the top, while the middle part of the overlying colluvium is ca. 4.8 ka. The relation between the lower fluvial units and the fault indicates that at least two large-scale earthquakes occurred in the Early Holocene, each one resulting in a 1–1.5 m high fault scarp. During this seismically active period, no coarse colluvial sediments were deposited along the fault trace and thus the region must have had low tectonic relief. The clear contact with the overlying coarse colluvium reflects a Middle Holocene rapid change to the present high, steep relief. This change was achieved by frequent, strong seismic events, which triggered colluvial processes and prevented stratification and soil formation on the slope. The soil on the present slope reflects a quiescent period that has lasted at least several hundred years, during which stress has accumulated and seismic risk increased.

Relief Inversion in the Avrona Playa as Evidence of Large-Magnitude Historical Earthquakes, Southern Arava Valley, Dead Sea Rift

The Arava Valley section of the Dead Sea Transform (DST) in southern Israel is characterized by the absence of seismic activity in recent times. However, paleoseismic analysis of sediments in the Avrona Playa, a pull-apart basin along the DST, reveals that at least six M > 6 tectonic events have affected the Avrona playa in the last 14,000 yr. The recurrence interval of the events is approximately 2000 yr. Trenched normal faults and push-up ridges in the playa show that the upper 2 m of the deformed sedimentary sequence consists of playa deposits with uniform soil development. The deformed sediments and the soil are typical of basins with an endoreic fluvial system. Based on the limiting age of the sequence and the extent of soil development, faulting in the playa, followed by compression and uplift, occurred in the last 1000 yr. This most recent tectonic event displaced the surface by at least 1 m, consistent with a M > 6.5 earthquake. This earthquake changed the morphology of the Avrona Playa from a closed system with internal drainage to an open basin, resulting in relief inversion. The seismic quiescence in the Arava may indicate a seismic gap in this segment of the DST.

Slope Movements Caused by The Three Large Earthquakes of Hokkaido, 1993-1994

Three large earthquakes of Kushiro-oki 1993, Hokkaido-nansei-oki 1993 and Hokkaido-toho-oki 1994, induced many landslides in Hokkaido. We review the topographic and geologic environments, types, and morphologic features of the landslides. Large varieties of type, scale, length of runout and degree of rupture of sliding body characterize the earthquake-induced slope movements. There were some remarkable features as vertical cracks of main scarp and shattered earth formed by the earthquake vibration in each damaged slope. Most rockslides were bench-like shape and their length was shorter than width. These features of damaged slope may be useful index for slope assessments, disaster investigation and paleoseismic analysis.

Use of liquefaction-induced features for paleoseismic analysis — An overview of how seismic liquefaction features can be distinguished from other features and how their regional distribution and properties of source sediment can be used to infer the location and strength of Holocene paleo-earthquakes

Liquefaction features can be used in many field settings to estimate the recurrence interval and magnitude of strong earthquakes through much of the Holocene. These features include dikes, craters, vented sand, sills, and laterally spreading landslides. The relatively high seismic shaking level required for their formation makes them particularly valuable as records of strong paleo-earthquakes. This state-of-the-art summary for using liquefaction-induced features for paleoseismic interpretation and analysis takes into account both geological and geotechnical engineering perspectives. The driving mechanism for formation of the features is primarily the increased pore-water pressure associated with liquefaction of sand-rich sediment. The role of this mechanism is often supplemented greatly by the direct action of seismic shaking at the ground surface, which strains and breaks the clay-rich cap that lies immediately above the sediment that liquefied. Discussed in the text are the processes involved in formation of the features, as well as their morphology and characteristics in field settings. Whether liquefaction occurs is controlled mainly by sediment grain size, sediment packing, depth to the water table, and strength and duration of seismic shaking. Formation of recognizable features in the field generally requires a low-permeability cap above the sediment that liquefied. Field manifestations are controlled largely by the severity of liquefaction and the thickness and properties of the low-permeability cap. Criteria are presented for determining whether observed sediment deformation in the field originated by seismically induced liquefaction. These criteria have been developed mainly by observing historic effects of liquefaction in varied field settings. The most important criterion is that a seismic liquefaction origin requires widespread, regional development of features around a core area where the effects are most severe. In addition, the features must have a morphology that is consistent with a very sudden application of a large hydraulic force. This article discusses case studies in widely separated and different geological settings: coastal South Carolina, the New Madrid seismic zone, the Wabash Valley seismic zone, and coastal Washington State. These studies encompass most of the range of settings and the types of liquefaction-induced features likely to be encountered anywhere. The case studies describe the observed features and the logic for assigning a seismic liquefaction origin to them. Also discussed are some types of sediment deformations that can be misinterpreted as having a seismic origin. Two independent methods for estimating prehistoric magnitude are discussed briefly. One method is based on determination of the maximum distance from the epicenter over which liquefaction-induced effects have formed. The other method is based on use of geotechnical engineering techniques at sites of marginal liquefaction, in order to bracket the peak accelerations as a function of epicentral distance; these accelerations can then be compared with predictions from seismological models.

Use of landslides for paleoseismic analysis

In many environments, landslides preserved in the geologic record can be analyzed to determine the likelihood of seismic triggering. If evidence indicates that a seismic origin is likely for a landslide or group of landslides, and if the landslides can be dated, then a paleo-earthquake can be inferred, and some of its characteristics can be estimated. Such paleoseismic landslide studies thus can help reconstruct the seismic history of a site or region. In regions that contain multiple seismic sources and in regions where surface faulting is absent, paleoseismic ground-failure studies are valuable tools in hazard and risk studies that are more concerned with shaking hazards than with interpretation of the movement histories of individual faults. Paleoseismic landslide analysis involves three steps: (1) identifying a feature as a landslide, (2) dating the landslide, and (3) showing that the landslide was triggered by earthquake shaking. This paper addresses each of these steps and discusses methods for interpreting the results of such studies by reviewing the current state of knowledge of paleoseismic landslide analysis.

Characterization of barium getters for television tubes

Paleoseismic analysis of the Azaz fault segment of the Dead Sea Fault (northern Israel), indicates that this region was subjected to intermittent periods of strong seismicity and quiescence during the latest Pleistocene and the Holocene. The Azaz fault forms the eastern margin of the Hula Valley, a pull-apart basin between two left-stepping segments of the Dead Sea Fault. The fault is currently inactive, but it displaces a 25–30 ka travertine in the northeastern corner of the Hula Valley and near-surface marsh sediments inside the valley. Two trenches excavated across a 15–20 m high fault scarp near Kefar Szold expose fluvial and colluvial sequences showing clear evidence of recent tectonics. One trench exposes well sorted, bedded alluvial sediments comprising two upward-fining units, each capped by a weakly developed paleosol. The sediments were deposited on the down-faulted block and are bounded in the east by the fault scarp. The second trench uncovers fine colluvial sediments cross-cut by a wide fault-parallel fissure filled by collapsed sediments. In both trenches, the lower sedimentary unit is capped by a coarse colluvium containing boulders up to 1.5 m in size. The colluvium shows no clear bedding and has a weakly developed paleosol on top. Optically stimulated luminescence dating of the lower fluvial sequence shows that its age ranges between 12 ka at the base to 6 ka at the top, while the middle part of the overlying colluvium is ca. 4.8 ka. The relation between the lower fluvial units and the fault indicates that at least two large-scale earthquakes occurred in the Early Holocene, each one resulting in a 1–1.5 m high fault scarp. During this seismically active period, no coarse colluvial sediments were deposited along the fault trace and thus the region must have had low tectonic relief. The clear contact with the overlying coarse colluvium reflects a Middle Holocene rapid change to the present high, steep relief. This change was achieved by frequent, strong seismic events, which triggered colluvial processes and prevented stratification and soil formation on the slope. The soil on the present slope reflects a quiescent period that has lasted at least several hundred years, during which stress has accumulated and seismic risk increased.