Tectonic Taphrogenesis and Paleoseismic Records from the Yishu Fault Zone in the Initial Stage of the Caledonian Movement

The Yishu fault zone （mid-segment of the Tanlu fault zone） was formed in the Presinian. Periodic tectonic activities and strong seismic events have occurred along the fault zone. During the initial stage of the Caledonian Movement, with the proceeding of the marine transgression from the Yishu paleo-channel to the western Shandong, uneven thick sediments, composed mainly of sand, mud and carbonates of littoral, lagoon, and neritic facies, were deposited in the Yishu fault zone and western Shandong, and constructed the bottom part of the Lower Cambrian consisting of the Liguan and Zhushadong formations. Through field observations and the lab-examinations, various paleoseismic records have been discovered in the Liguan Formation and the Zhushadong Formations of the Yishu fault zone and its vicinity, including some layers with syn-sedimentary deformation structures that were triggered by strong earthquakes （i.e. seismite, seismo-olistostrome, and seismo-turbidite）. Paleoseismic records developed in the Zhushadong Formation are mainly seismites with soft-sediment deformation structures, such as liquefied diapir, small liquefied-carbonate lime-mud volcano, liquefied vein, liquefied breccia, convolute deformation （seismic fold）, graded fault, soft siliceous vein, and deformation stromatolite, as well as seismites with brittle deformation structures of semiconsolidated sediments. Paleoseismic records preserved in the Liguan Formation are not only seismo-olistostrome with a slump fold, load structure, and ball-and-pillows, but also seismo-turbidite with convolution bedding, graded bedding and wavy-bedding. However, in the western Shandong area, the closer to the Yishu fault zone, the greater the thickness of the Liguan Formation and the Zhushadong Formation, the greater the number and type of layers with paleoseismic records, and the higher the earthquake intensity reflected by associations of seismic records. This evidence indicates that tectonic taphrogenesis accompanied by strong earthquake events occurred in the Yishu fault zone during the initial stage of the Caledonian Movement, which embodied the break-up of the Sino-Korean Plate along the Paleo-Tanlu fault zone at that time.

History of Paleoseismic ActivityAlong the Hohhot Segment of Daqingshan Piedmont Fault in the Late Quaternary

A detailed study on geomorphic surfaces and a set of trenches on the Hohhot segment of Daqingshan piedmont fault at three sites, Kuisu, Ulan Blang, and Qingshan Grassland, revealed 7 paleoseismic events occurred along the fault segment since 19 ka BP. Those events occurred at 18.75±.75 ka, 16.97 ±.96 ka, 14.65±.67 ka, 11.82±.69 ka, 9.45±.26 ka, 6. 83±.26 ka, and 4. 50 ±0. 23 ka BP, respectively, and their average recurrence interval is 2375±432 years. From the results of constraining fault displacement and correlation between the sediments in these trenches, we found a complete paleoseismic activity history along the fault segment during this period of time.

Characteristics of Paleoseismic Activity Along the Tianqiaogou-Huangyangchuan Fault on the Eastern Section of the Qilian Mountains

The Tianqiaogou-Huangyangchuan fault lies east of the main peak, Lenglongling Mount, in the east part of the Qilian Mountains and is one of the major active faults on the eastern section of the Qilian Mountains. The fault is separated into two segments at Guanjiatai village, the eastern and western segments, and has undergone obvious movement since the Holocene. Six trenches were excavated to study the pa!eoseismic activity along the fault. Integrated and comparative analysis of sediments in the trenches reveals 7 paleoseismic events and a historic earthquake on the fault since the Holocene. Their ages are： event Ⅰ is （10743 ± 343 ）a BP,event Ⅱ （9038 ± 39）a BP, event Ⅲ （7050 ± 577）a BP, event Ⅳ （4847 ± 185）a BP, event Ⅴ（3562 ± 190）a BP, event Ⅵ （2476 ±194） a BP, and event Ⅶ（1505 ± 253）, respectively, and event Ⅷ is the 1927 Gulang Ms8. 0 earthquake. It indicates that the fault might have contributed to the 1927 Gulang Ms8.0 earthquake. The temporal and spatial distribution of the paleoseismic events is relatively uniform and is characterized approximately by a quasiperiodic recurrence.

Sediment Deformations Due to Paleoseismic Events

There are many different processes generating soft-sediment deformation. This paper is confined to deformations generated by paleoseismic events in Sweden. The Paleoseismic Catalogue of Sweden includes 66 events. The structural characteristics and driving forces of liquefaction are discussed in details. “Crypto-deformations” refer to a special type of fluidization not affecting the sedimentary bedding itself, but the internal orientation of the ChRM and AMS carrying particles. Extensive turbidites are formed at some events. They constitute useful “marker-varves”. Out of the 66 paleoseismic events, 31 are dated by varves as to a single year (in one case even to the season of a year). Tsunamites are recorded from 19 of the paleoseismic events;some with wave-heights up to 15 - 20 m.

Liquefaction Structures from a High-Magnitude Paleoseismic Event at about 12,400 C14-Years BP in Southern Sweden

The Swedish catalogue of paleoseismic events includes 64 separate events. The seismic activity was especially high, in magnitude and frequency, in the Late Glacial with peak rates of glacial isostatic uplift. At about 12,400 C14-years BP (14,600 cal?yrs BP), there was a very strong event on the Swedish west coast. The magnitude was estimated at M > 8. It was linked to intensive liquefaction and a major tsunami event. In this paper we describe sedimentological structures of liquefaction, ground shaking and tsunami wave actions from the Hunnestad gravel pits, to the east of the city of Varberg on the Swedish West Coast. The liquefaction structures documented offer impressive and educational insight into the process of liquefaction at high-magnitude earthquakes.

Recent geodynamics of major strike-slip zones

The subject of this study is strike-slip fault zones, where temporal variations of accumulation in strike-slip deformation complicate the standard process of deformation accu- mulation and release during strong earthquakes. These temporal variations are expressed in the E1 Ghab segment of the Dead Sea Transform zone （DST, Eastern Mediterranean） and in the Talas-Fergana fault zone （Central Asia）. According to Global Positioning System （GPS） data, the strike-slip deformations within these zones are not now accumulating or are accumulating at a rate that is significantly less than their average rate during the Holocene and Quaternary or the Pliocene-Quaternary. Simultaneously, weak transverse shortening has been measured in both zones by GPS. In both of these zones, strong earthquakes have not registered within the XX century, yet epochs of intensified seismicity （strong earthquakes） took place throughout history. In the southern and central parts of the E1 Ghab zone, there is evidence of 30 strong historical earthquakes of Ms ≥ 5.7; however, no instrumental earthquakes of Ms 〉 5 have been identified. The temporal distribution of seismic energy released by these earthquakes demonstrates a 350 ± 50-year cycle. Values for the seismic energies released during the peak phases of these cycles are approximated by a sinusoid that suggests the possibility of a 〉1800-year cycle （＂hyper-cycle＂）, which began around the 3rd century, reached its maximum in the 12th century, and has continued until now. A combination of geological, archaeoseismological, and geodetic data show that the rate of sinistral strike-slip deformation varied in the fault zone, probably in conformity with the variation of seismicity during the ＂hyper-cycle.＂ In the Talas-Fergana fault zone, trenching and 14C dating that was correlated with right lateral offsets, gave a possible preliminary estimate of the average rates of the Late Holocene strike slip of about 10 mm per year, with a decrease in the SE direction to 4 mm-4.5 mm per year. These studies also showed that the slip in the Talas-Fergana fault zone was realized mainly during strong earthquakes. New trenching and 14C dating of paleoearthquake records identified the epoch of seismicity intensification dating to the XIV-XVII centuries. These paleoearthquakes could produce a total dextral slip at several meters. Therefore, consid- eration of these epochs was necessary to determine a calculated average slip rate during the Late Holocene.

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

The 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.

Thermoluminescence Dating of Colluvial Deposits and Its Application to Chronological Study of Paleoearthquakes

On the basis of studies of lithofacies features of colluvial deposits, applicability of thermoluminescence dating of the colluvial deposits at different lithofacies positions, and reliability of the dating result, the thermoluminescent ages of colluvial deposit from different types of faults were determined. From the above, the ages of paleoseismic events and their recurrence intervals on the related fault were deduced.

Underestimated seismic hazard in the south of the Issyk-Kul Lake region (northern Tian Shan)

The Tian Shan Mountains were formed in the result of the India-Eurasia collision, which leads to cre- ation of contrast high-mountain relief and world known seismic activity. The seismic catastrophes, recorded instrumentally, have occurred to the north of the Issyk-Kul Lake region. There are also known significant earthquakes with magnitude being about 7 in western and eastern parts of the mentioned lake region. Only in the south of the Issyk-Kul depression the strong earthquakes recorded by the seismic network were not known. Our recent study in the south of the lssyk-Kul Lake region has revealed numerous active tectonic structures related to South Issyk-I（ul Fault： faults and folds, responsible for strong earthquakes＇ occurrence. These were historical and paleoseismic defornlations which led to changes in relief： fault scarps and significant rockslides. We have also found spectacular deformations in archeological monuments. All these deformations testify the location of epicentral areas of two strong historic （about llth and 16th （？） centuries AD） and paleoearthquakes （Holocene and Late Pleistocene）. Magnitude of ancient seismic events, according to parameters of the revealed fault scarps, were Ms 〉 7 and seismic intensity I 〉 IX. All revealed seismic deformations are located to adyrs （piedmonts） of the Terskey Ala-Too range bordered of the lssyk-Kul Lake depression in the south. Their formation is described by the model of a fault which rupture plane becomes shallower southward. This model is complicated by the presence of reverse thrusts. Here, we should admit the existence of a single zone of South lssyk-Kul Fault which is a long-lived feature which separates the structures with the different regime of movements during the Neotectonic time. All obtained data led us to a conclusion of significant underestimation of the seismic hazard in southern lssyk-Kul Lake region.

Late-Quaternary Movement Along the Sertengshan Piedmont Fault and a Model for Segmentation of Its Rupture

Analysis and study of the geometrical structure of the fault, tectonic features of late Quaternary movement, paleoseismic activity, and structural characteristics of boundaries between segments of the Sertengshan piedmont fault permitted us to preliminarily determine the following 4 active segments of the fault: the Wujiahe segment (from Dongwugai Gully to Dahoudian Village), Wujumengkou Dongfeng Village segment (from Dahoudian to Delingshan), Dashetai segment (from Delingshan to Xiaoshetai Gully mouth), and the Ulan Hudong segment (from Xiaoshetai Gully mouth to Tailiang). The boundaries between them are the Dagoudian mountain spur, the Delingshan Mountain spur and the step zone at Xiaoshetai Gully mouth, respectively. The segments are independent for seismic activity. However, it is possible that joint ruptures between Wujiahe and Wujumengkou Dongfeng Village segments and between Dashetai and Ulan Hudong segments may occur.

Late-Quaternary strong earthquakes on the seismogenic fault of the 1976 M_s7.8 Tangshan earthquake,Hebei,as revealed by drilling and trenching

Composite borehole profiling combined with trenching is an effective way to acquire evidence of past ruptures of buffed active faults. In this study, three composite borehole profiles and a large-scale trench excavation were carded out across the surface rupture zone of the 1976 Ms7.8 Tangshan earthquake. The following three major conclusions have been reached. （1） The surface rupture zone of the 1976 earthquake extends more than 47 km long to the south of Tangshan city, passing to the west of Sunjialou, to Daodi town in Fengnan County, to Xihe in Fengnan County. （2） The surface rupture zone is divided into south and north branches. The north branch has mainly fight-lateral strike-slip motion, and the vertical displacement of the surface is up on the west and down on the east. On the other hand, the vertical displacement of the south branch is up on the east and down on the west, accompanied by some right-lateral slip. Such a faulting style cannot be explained by the movement of a single normal or reverse fault, but is consistent with the vertical displacement field induced by the fight-lateral strike-slip of the fault belt. The drilling and trenching data from this study verify that such activity continued through the Late Quaternary on the Tangshan Fault. （3） The fault planes exhumed by trenching and the dislocations of strata revealed by the boreholes indicate that multiple faulting events occurred on the Tangshan Fault in the Late Quaternary. The timing of three ruptures prior to the 1976 earthquake was 7.61-8.13, 〉14.57, and 24.21-26.57 ka BP. Counting the earthquake of 1976, the recurrence interval of the four strong events is about 6.7 to 10.8 ka. On one of the three borehole profiles, the Niumaku profile, nine faulting events were detected since 75.18 ka BP with an average interval of 8.4 ka. In addition, this paper also discusses the difference between the Late Quaternary sedimentary environments to the north and south of Tangshan city based on stratum dating.

Recurrence characteristics of late-quaternary strong earthquakes on the major active faults along the northern border of Ordos block

Through study on trenches, analysis of recurrence characteristics and recurrence interval cluster/gap of strong earthquakes along the major active faults on the northern border of Ordos block, we found 62 paleoearthquakes that occurred in the late Quaternary, including 33 earthquakes occurring in the Holocene. The recurrence characteristics of the paleoearthquakes are different at three levels, segments, faults, and fault zones. The strong seismic sequence on the independent segments is mostly characterized by long- and short-interval recurrences, while that on the faults and in fault zone is characterized clearly by random and cluster recurrences. Results of the moving window test indicate that the probabilities of "temporal cluster or gap", caused by random coincidence as opposed to intersegment contagion, are 64% and 70% for the Serteng piedmont fault and for the south-border fault of Wula Mountains, respectively, no clear interaction among the segments of each fault; while the probability is 26.8% for the whole fault zone, suggesting a clear interaction among the faults of this fault zone. These recurrence characteristics may imply an effect of the entire block motion on the recurrence of strong earthquakes. Moreover, the elapsed time for the Wujumeng Pass-Dongfeng Village segment of Serteng piedmont fault and the Tuzuo Banner-Wusutu and the Hohhot segments of Daqingshan piedmont fault has exceeded the average recurrence interval, hence these three segments may be the possible places for future strong earthquakes.

First Discovery of North-South Striking Normal Faults near the Potential Eastern End of Altyn Tagh Fault

The Altyn Tagh fault is the northern boundary of Tibetan Plateau. As one of the most well-known strike-slip fault in the world, great achievements on tectonic deformation and Late Qua- ternary slip rate have been made. However, there is a long-lasting debate on whether the Altyn Tagh fault extends into the Jinta Basin or even eastward. In this paper, we use satellite image interpretation, field investigation, trench excavation, and optical stimulated luminescence dating to study newly found NS striking scarps in the eastern end of Jinta Nan Shan. The results are as follows： firstly, a group of normal faults develop on terrace T2 of Heihe River, the total length amounts to -40 km, total scarp height is 304-5 m; secondly, four paleoseismic events have been interpreted from three trenches, approximate ages of events are 79.97±19.14 ka BP, 62.55±13.10~55.41±10.77 ka BP, before 16.89±2.08 ka BP, 8.52±1.49 ka BP, respectively; thirdly, just like NS normal faults in the western end of Altyn Tagh fault, the newly found NS extensional faults are likely the terminating tectonics of the eastern end of Altyn Tagh fault, the large Altyn Tagh fault may end in the eastern end of Jinta Nan Shan.