Palaeoseismic Events Research Articles

Dating early Holocene palaeoseismic event(s) in the Gulf of Bothnia, Baltic Sea

Dating early Holocene palaeoseismic event(s) in the Gulf of Bothnia, Baltic Sea

The Fenris Wolf in the Nordic Asa creed in the light of palaeoseismics

Abstract The Nordic Asa Creed talks about a giant wolf, ‘the Fenris Wolf’, that was trapped and chained deep in the mountains. When he howled, the ground trembled violently and fractured. With the discovery of frequent high-magnitude palaeoseismic events in Sweden not only in de-glacial time but also in Late Holocene time, it seems both natural and logical that the Fenris tale refers to frightening earthquake events in the past. Once again tales and sagas have been shown to be rooted in facts.

Submarine Holocene sedimentary disturbances in the Olkiluoto area of the Gulf of Bothnia, Baltic Sea: a case of postglacial palaeoseismicity

High-resolution echo soundings were used to study the fault activity in the Olkiluoto area of the Gulf of Bothnia, southwestern Finland. Echo-sounding profiles in Holocene submarine sediments show normal faults, structures related to gas or groundwater seepage, submarine slides and slumps, and debris-flow type structures. The faults and other ‘disturbance structures’ occur along two bedrock lineaments. All faults occur at the same stratigraphical level, whose age is estimated at ∼10,700 calendar years BP (∼9500 radiocarbon years BP). It is suggested that their movement has been triggered by palaeoseismic event(s) when the Late Weichselian ice sheet was retreating from the site and bedrock stresses were released through lineaments and fracture zones. These are the first observations of postglacial fault movements in Quaternary sediments from southern Finland, but, the timing of these movements is contemporaneous with the incidence of postglacial bedrock faulting (∼9000–10,000 radiocarbon years BP) in northern Fennoscandia. The origin of the gas/groundwater seepages remains unclear. Their reflections in the echo-sounding profiles imply that part of the gas is derived from the organic-bearing Litorina and recent gyttja clays. However, at least some part of the gas is derived from the bedrock (deep gas).

Quaternary sediments in the Dien Bien Phu fault zone, NW Vietnam: a record of young tectonic processes in the light of OSL-SAR dating results

The Dien Bien Phu fault zone (DBP), orientated NNE to N, is one of the most seismically active zones in Indochina. In NW Vietnam, this zone is 160 km long and 6–10 km wide, cutting sedimentary and metamorphic rocks of the Late Proterozoic, Palaeozoic and Mesozoic age, as well as Palaeozoic and Late Triassic granitoids. Along the DBP relatively small, narrow pull-apart basins occur, the three largest of which (Chan Nua, Lai Chau and Dien Bien Phu) have been studied in detail. All of them are bounded by sinistral and sinistral-normal faults, responsible for offset and deflected drainage, presence of numerous shutter ridges and displaced terraces and alluvial fans. The normal component of motion is testified to by well-preserved triangular facets on fault scarps, highly elevated straths in river watergaps, overhanging tributary valleys, as well as high and uneven river-bed gradients. Our observations indicate a minimum recent sinistral offset ranging from 6–8 to 150 m for Holocene valleys to 1.2–9.75 km for middle–late Pleistocene valleys in different fault segments. The thickness of Quaternary sediments varies from 5–25 m in the Lai Chau area to some 130 m in the Dien Bien Phu Basin. In the Lai Chau Basin, the middle terrace (23 m) alluvia of Nam Na River at Muong Te bridge have been optically stimulated luminescence/single aliquot regenerative dose technique (OSL-SAR) dated at 23–40 to 13 ka. These sediments were normal-faulted by some 11 m after 13 ka, and mantled by vari-coloured slope loams, 8–12 m thick, containing colluvial wedges composed of angular debris. These wedges were probably formed due to at least three palaeoseismic events postdating 6 ka. In the Dien Bien Phu Basin, in turn, alluvium of the upper Holocene terraces has been OSL-SAR dated to 6.5–7 and 1.7–1.0 ka, whereas the younger (sub-recent) terrace sediments give ages of 0.5–0.2 ka. Displaced terraces and alluvial fans allow us to suppose that the sinistral and sinistral-normal faults bounding narrow pull-apart basins in the southern portion of the DBP fault reveal minimum rates of left-lateral strike-slip ranging from 0.6 to 2 mm/year in Holocene and 0.5–3.8 mm/year in Pleistocene times, whereas rates of Holocene uplift tend to attain 1 mm/year north of Lai Chau and 0.4–0.6 mm/year west of Dien Bien Phu. More precise estimations, however, are difficult to obtain due to poor age control of the displaced drainage. Rates of Quaternary strike-slip are comparable with those of the Red River fault; the sense of movement being, however, opposite. Taking into account the presence of two phases of Late Cenozoic strike-slip of contrasting sense of motion, as well as the geometry of the two fault zones, we hypothesize that the Red River and Dien Bien Phu faults are conjugate faults capable of generating relatively strong earthquakes in the future.

Deformation structures in Plio- and Pleistocene sediments (NW Bohemia, Central Europe)

Abstract The small intracratonic Cheb (Eger) Basin in NW Bohemia (Central Europe) is characterized by swarm earthquakes, many mineral springs and mofettes with upper mantle CO 2 degassing and by neotectonic graben and basin structures. Especially in non-lithified Upper Pliocene clay formations of the basin, a variety of deformation patterns is exposed. They include non-tectonic and tectonic activity and comprise faulting and folding from µm- to km-scale. Previously unrecognized N-S- and ENE-striking faults are sites of mantle degassing and seismic activities. Confined-layer deformation and liquefaction structures hint to palaeoseismic events and gas escape activity. Cleavage-like arranged clay mineral plates represent the microfabric of clay within fault zones. For the first time the degassing channels of Upper Mantle fluids/gases through the Pliocene clay sediments can be documented: µm-scale micro-tubes were produced by the opening of Riedel shear planes induced by fault movements.

Palaeoseismic Events in Karst Terrains along the Northern Bulgarian Black Sea Coast

AbstractThe study of the palaoseismic events in the karst terrains of the Bulgarian Black Sea coast is a very important up‐to‐date problem. The investigated region is one of the highest‐energy regions in Bulgaria with established and recorded catastrophic historic and contemporary earthquakes. The terrain is subjected to the influence not only of its own earthquake foci but also of those in Romania and Russia. The palaeoearthquakes that caused considerable disturbances in the karst terrains along the Northern Bulgarian Black Sea coast have left significant traces. They caused disturbances in the environment and the relief (rearrangement of the surface and ground water karst basins, partially or entirely collapsed caves, deformed caves, oil, gas and salt intrusions and gravitationally formed caves). The ecological consequences in historic and contemporary aspects were catastrophic. The palaeoseismic dislocations were formed as a result of global, regional and local geodynamic events related with the destruction of the Moezian platform and the regional extension of the Black Sea basin. The time of their display and their spatial interrelations were established as a result of complex investigations accompanied by original documents.

Postglacial fault movement and palaeoseismicity in western Scotland: A reappraisal of the Kinloch Hourn fault, Kintail

The Kinloch Hourn fault is the most prominent of a number of suspectedpostglacial faults in the western Scottish Highlands. These faults areinterpreted to have been reactivated by repeated large (M > 6)palaeoseismic events following deglaciation 10,000–13,000 years ago.Based on inferred deflections of drainage courses, previous studies of thefault have estimated 160 ± 40 m cumulative left-lateral displacementalong a 14 km long active segment during postglacial times. Reportedsoft-sediment deformation phenomena imply that activity on the KinlochHourn fault has persisted into the late Holocene, with the most recentmovement having been associated with a magnitude 5.5–6.0 surface-faultingevent between 3500 and 2400 years ago. The marked contrast betweensuch palaeoseismic activity and the present-day seismic quiescence ofwestern Scotland has stimulated this critical reappraisal of the KinlochHourn fault.This paper reassesses the key lines of evidence for postglacial fault activityand palaeoseismicty on the Kinloch Hourn fault, combining the analysis of1:15,000-scale air photos, field-based geomorphic mapping andpalaeoenvironmental investigations. Our reappraisal of inferred drainagedeflections across the fault contends that previous reports of significant(102 m) left-lateral slip on the fault during the Holocene arespurious. Instead, incidences of Holocene channel abandonment along thefault line are non-synchronous and probably reflect non-tectonic drainagechanges. The timing of soft-sediment deformation in the vicinity of the faultis revised to an early Holocene date (8990–8580 calendar years BP), whichis in accord with both the palaeoenvironmental history of the site andconsistent with published ages of earthquake-induced liquefactionphenomena documented elsewhere in western Scotland. An alleged recent(post-2400 radiocarbon years BP) ground rupture on the fault isquestioned in the light of uncertainty about both the nature of the faultedsoil deposit and the late Holocene age attributed to it.The study concludes that there is no convincing evidence for postglacialsurface rupture on the Kinloch Hourn fault and speculates that the casefor significant (101–102 m) postglacial movement on otherfaults in western Scotland may be similarly `unproven'.

Soft-sediment deformation structures interpreted as seismites in middle-late Pleistocene aeolian deposits (Apulian foreland, southern Italy)

Soft-sediment deformation structures in middle-late Pleistocene deposits of Torre San Gennaro (Brindisi—southern Italy) have been analysed. From a morphologic point of view, the deformational structures are represented by deformed cross-bedding and large injection structures. They are restricted to aeolian sediments, and the mechanism of deformation is related to liquefaction and/or fluidization processes. The liquefaction and/or fluidization processes have been interpreted as seismic-induced after consideration of all other possible trigger agents. The discussion about the possible source areas of the palaeoseismic event was carried out through the analysis both of the general magnitude/distance relations and the main structural features of the study zone. In conclusion we consider the key criteria for trigger mechanism interpretation of soft-sediment deformation structures in aeolian deposits and the actual feasibility of using aeolian sediments for the palaeoseismic studies.

Timing and return period of major palaeoseismic events in the Shillong Plateau, India

The close temporal occurrence of four great earthquakes in the past century, including the great Assam earthquake of 1897 in the Shillong Plateau, necessitated examination of the palaeoseismicity of the region. The results from such investigation would definitely aid in addressing the problem of the earthquake hazard evaluation more realistically. Our recent palaeoseismological study in the Shillong Plateau has led us to identify and provide geological evidence for large/major earthquakes and estimate the probable recurrence period of such violent earthquakes in parts of the Shillong Plateau and the adjoining Brahmaputra valley. Trenching along the Krishnai River, a tributary of the River Brahmaputra, has unravelled very conspicuous and significant earthquake-induced signatures in the alluvial deposits of the valley. The geological evidence includes: (1) palaeoliquefaction features, like sand dykes and sand blows; (2) deformational features, like tilted beds; (3) fractures and syndepositional deformational features, like flame structures caused by coeval seismic events. Chronological constraints of the past large/major earthquakes are provided from upper and lower radiocarbon age bounds in the case of the palaeoliquefaction features, and the coeval timing of the palaeoseismic events is obtained from the radiocarbon dating of the organic material associated with the deformed horizon as well as buried tree trunks observed wide distances apart. Our palaeoseismic measurements, which are the first from the area, indicate that the Shillong Plateau has been struck by large/major earthquakes around 500±150, 1100±150 and >1500±150 yr BP, in addition to the well-known great seismic event of 1897, thereby the 14C dates indicate a recurrence period of the order of 500 yr for large earthquakes in the Shillong Plateau.

Analysis and study of the large earthquake risk in Yanqing-Huailai basin

On the basis of study results of deep sounding in the Yanqing-Huailai basin, the shallow active tectonics, palaeoseismic events, seismic activity, distribution of crustal stress field and other related data are combined to study the earthquake risk of the basin comprehensively. Meanwhile, the comparison of deep structures between the basin and some other earthquake regions such as the Xingtai area is made. It is thought that there is the background of deep structures for occurrence of moderate and strong earthquakes in the Yanqing-Huailai basin and its periphery, and the possibility for an M=7 earthquake to occur there cannot be excluded.

First palaeoseismological results from Greece

This is a brief account of our approach to trends in palaeoseismological research that are currently emerging in Greece, with the application of modern investigative methods practised world-wide in active tectonic zones. These techniques include fault stratigraphy in trenches, and dating recent fault reactivations in order to understand and distinguish palaeoseismic events along specific segments of active faults, named Gerakarou (Mygdonia Basin, Thessaloniki area), Palaeochori Fault (Kozani-Grevena, Western Macedonia), Souli (Petousi, Epirus), and Volos-Larissa (Thessaly plain). Four palaeoearthquakes were investigated on the Gerakarou fault segment, with a uniform slip rate and return period around 7000 years. In Western Macedonia "aseismic areas" the Servia-Palaeochori recently activated fault shows a -3500 year quiescence. Three coseismic events on the Souli Fault pre- and post-date to 26000 year deposits.

Late Holocene relative sea level changes in SW Crete: evidence of an unusual earthquake cycle

Coastal challenges ill West Crete ill the last 4000 years can be described as a series of 11 relatively small (25 cm on the average) land subsidences alternating with short (150-250 year long) relatively still stands of the sea level. At 1500 B.P. an up to 9 m episodic relative land uplift and tilting of this part of the island occurred, but since then no significant coastal changes have been identified. There is strong evidence that these Late Holocene coastal changes are not a product of fluctuations of sea level, but reflect palaeoseismic events. The sequence of the latter is at variance with models of seismic deformation deduced from a wide range of observations in different tectonic environments, including coastal uplifts near major trenches: according to these models, strain buildup and release through earthquakes is described as a cyclic and rather uniform process, the earthquake cycle. In this process, the permanent seismic deformation accumulates after each earthquake to produce geological features, while the long-term deformation rate is approximately equal to the short term one. Obviously this is not the case with West Crete. The unusual pattern of seismic deformation in this island has been observed in other cases as well, but its explanation is not easy. The juxtaposition of different earthquake cycles, variations in the source and rate of stress or internal deformation of the uplifted hanging wall of a thrust in the pre-seismic period are some possible explanations for this unusual pattern of earthquake cycle in Greece.

Late-Holocene shoreline changes related to palaeoseismic events in the Ionian Islands, Greece

A systematic multidisciplinary survey on the coasts of the Ionian Islands, founded on 26 new radiocarbon accelerator mass spectrography (AMS) dates, has revealed the occurrence of sectors which were uplifted (seismo)tectonically during the late Holocene. In Corfu, two uplift movements of about 0.8m each took place in the central part of the island: one of them around 790-400 cal. BC, and also at a more recent, undetermined date. In Levkas, up-and-down tectonic movements of metric order governed late-Holocene relative sea-level changes, at least in the northern part of the island; submergence of at least 2.5 m occurred since 2400 years ago, with a possible spasmodic subsidence around cal. AD 500-700. In Cephalonia, two vertical displacements affected most of the island, around cal. AD 350-710 and in AD 1953; both movements resulted in uplift in the southeastern part of the island. Submergence seems to predominate round Ithaca. Lastly, in Zante, clear evidence of a Holocene crustal block movement is limited to the southeastern peninsula, where an uplift of 0.95 ± 0.15 m took place, probably coseism ically, around the period cal. AD 200-500. The time ranges of uplift in Cephalonia and Zante, and of possible subsidence in Levkas, correspond with a period of regional tectonic paroxysm, between the middle of the fourth century AD and the middle of the sixth century AD; this has already been documented in several areas of the eastern Mediterranean, notably in the Gulf of Corinth, the southern Hellenic arc, Turkey, Cyprus, the Lebanon and Syria.

The 1953 earthquake in Cephalonia (Western Hellenic Arc): coastal uplift and halotectonic faulting

SUMMARY Geomorphological, marine biological and radiometric data in combination with earlier reports reveal that the M, =7.2, 1953 Cephalonia earthquake, the most destructive but least studied earthquake in Greece this century, was associated with a 0.3-0.7m quasi-rigid-body uplift and westward tilting of the central part of the island. Another palaeoseismic event, around 1500 yr BP, associated with coastal uplifts was also identified. Structural data indicate that the 1953 uplift is bounded by two subparallel, east-dipping major reverse faults and corresponds to a piston-like motion. This structurally unusual pattern of seismic deformation is detached from the deformation of the basement (conspicuously a thrust) and different from the long-term deformation pattern of the area; it is probably due to the particularities of salt tectonics: a -1500m thick salt layer acts as a regional dCcollement, while thinner layers are sandwiched between the carbonate thrust sheets that compose the overburden and reduce their friction during fault movement. This crustal anisotropy is responsible for the observed anomalous attenuation of seismic waves during the 1953 and historical earthquakes. The 1953 seismic surface deformation mimics long-term halotectonic patterns, but is not directly indicative of the regional stress-field, for it reflects uplift-induced stresses only.

Seismic uplift of the harbour of ancient Aigeira, Central Greece

The Mavra Litharia cove, between Akrata and Derveni, in the North Peloponnesian coast (Central Greece), has been identified as the site of the harbour of the Hellenistic Aigeira, one of the very few natural harbours along the uplifting, fault-controlled North Peloponnesian coast.Geomorphological, marine biological and archaeological data as well as radiocarbon dating of marine fossils testify to a 2 m relative land uplift since Hellenistic times (around 2000 years BP), part of which (1 m at least) was probably seismic, dated to the Byzantine period (AD 900-1200). This palaeoseismic event, as well as others deduced from archaeological data, are not included in the historical seismology records, but had probably dramatic impacts on the economic and cultural history of ancient Aigeira.The amplitude of uplift at Mavra Litharia is of the same order of magnitude as submersion dominating the Aegean and, with the exception of the arc, the higher Holocene uplift rate recorded in this area and the surrounding regions. This result is consistent with the Quaternary uplift history of North Peloponnesus.

Seismic uplift of the harbour of ancient Aigeira, Central Greece

Abstract The Mavra Litharia cove, between Akrata and Derveni, in the North Peloponnesian coast (Central Greece), has been identified as the site of the harbour of the Hellenistic Aigeira, one of the very few natural harbours along the uplifting, fault-controlled North Peloponnesian coast. Geomorphological, marine biological and archaeological data as well as radiocarbon dating of marine fossils testify to a 2 m relative land uplift since Hellenistic times (around 2000 years BP), part of which (1 m at least) was probably seismic, dated to the Byzantine period (AD 900-1200). This palaeoseismic event, as well as others deduced from archaeological data, are not included in the historical seismology records, but had probably dramatic impacts on the economic and cultural history of ancient Aigeira. The amplitude of uplift at Mavra Litharia is of the same order of magnitude as submersion dominating the Aegean and, with the exception of the arc, the higher Holocene uplift rate recorded in this area and the surrounding regions. This result is consistent with the Quaternary uplift history of North Peloponnesus.

Palaeoseismic events recorded in Archaean gold-quartz vein networks, Val d'Or, Abitibi, Quebec, Canada

Archaean gold-quartz vein deposits are commonly hosted in high-angle reverse shear zones and are interpreted to have formed in a regime of horizontal compression and high fluid pressure environment. This paper presents the results of a combined structural and fluid inclusion study on three gold-quartz vein deposits of the Val d'Or area (Abitibi, Quebec) consisting of subhorizontal extensional veins and E-W steeply dipping shear veins. Crack-seal structures, tourmaline fibres, stretched quartz crystals and open-space filling textures indicate that the subhorizontal veins formed by hydraulic fracturing under supralithostatic fluid pressure. CO 2-rich and H 2 O + NaCl fluid inclusions, interpreted as two coexisting immiscible fluids, occur typically in microcracks of different orientations interpreted to have formed in the σ 1- σ 2 plane. Horizontal CO 2-rich fluid inclusion planes are contemporaneous with the opening of these veins (σ 3 vertical). Vertical H 2O + NaCl fluid inclusion planes, as well as some microstructures, such as deformed minerals, indicate that the same extensional veins have experienced episodic vertical shortening (σ 3 horizontal) alternating with the opening events. Deformation and slip/opening also occurred in shear veins in which preferred orientation of fluid inclusion planes is not clear, except that the H 2O + NaCl fluid inclusion planes tend to be oriented at high angles to the slip direction. The successive opening and collapse events in subhorizontal extensional veins are correlated with deformation and slip/opening events in shear veins, respectively, and are attributed to cyclic fluid pressure fluctuations in the system. They are thus consistent with the fault-valve model: sudden drop in fluid pressure from supralithostatic to lower values induces fluid unmixing and occurs immediately post-failure following seismic rupturing along the shear zone. Sealing of the shear veins allows the fluid pressure to build up again and the subhorizontal extensional veins to form. The intermittent change in orientation of σ 3 in horizontal extensional veins is ascribed to a total shear stress release along the neighbouring shear veins after rupture. The complex internal structures of the gold-quartz veins provide an excellent record of Archaean seismic activity along high-angle reverse faults.