The Lake Edgar Fault: an active fault in Southwestern Tasmania, Australia, with repeated displacement in the Quaternary
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The Lake Edgar Fault in Western Tasmania, Australia is marked by a prominent fault scarp and is a recently reactivated fault initially of Cambrian age. The scarp has a northerly trend and passes through the western abutment of the Edgar Dam, a saddle dam on Lake Pedder. The active fault segment displaces geologically young river and glacial deposits. It is 29 ± 4 km long, and dips to the west. Movement on the fault has ruptured the ground surface at least twice within the Quaternary and possibly the last ca. 25 000 years; the most recent rupture has occurred since the last glaciation (within the last ca. 10000 years). This is the only known case of surface faulting in Australia with evidence for repeated ruptures in the Late Pleistocene. Along its central portion the two most recent surface-faulting earthquakes have resulted in about 2.5 m of vertical displacement each (western side up). The Lake Edgar Fault is considered capable of generating earthquakes in the order of magnitude 61/2-71/4. The Gell River Fault is another fault nearby that was apparently also active in the Late Pleistocene. It has yet to be studied in detail but the scarp appears to be more degraded and therefore older than the most recent movement on the Lake Edgar Fault.Keywords:
Vertical displacement
AThe morphology of a 1,200-m-high bedrock mountain front in the Rio Grande rift of northern New Mexico demonstrates the persistence through Pliocene-Quaternary time of temporal and spatial patterns of late Quaternary rupture along the range-bounding fault zone. Detailed mapping of the surface trace of the fault zone suggests a complex geometric segmentation pattern consisting of four primary segments, each containing two to four 5- to 10-km-long subsegments. The central to south-central part of a subsegment or segment is defined by a narrow zone of single- to double-strand fault scarps commonly at the base of a reentrant in the range...
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Bedrock
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The authors have performed a series of researches on seismogeology,Quaternary structure and strata,and accomplished several tens of projects on engineering geology and engineering earthquakes in the middle and south region of Shandong Province in recent years.The results indicate that the Quaternary fault activities in this region shows unhomogeneity in temporal and spatial domains which were mainly displayed by the variations in the intensity and the clustering of fault activities and the limitation of the distribution of the late Quaternary active fault segments.As for the middle and south region of Shandong Province,active faults can be divided into two types:the first type is composed of active faults which were active between the mid time of mid Pleistocene and the early period of late Pleistocene,and the second includes active faults which were active between the mid and late periods of late Pleistocene and the early period of Holocene.The above mentioned two types of active faults can control the occurrence of earthquakes with different magnitudes,the former can control the occurrence of earthquakes with magnitude of about 5 5,while the latter with magnitudes between 6 and 7.
Early Pleistocene
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Early Pleistocene
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In recent times,some moderate-large earthquakes occurred in active folds and thrusts,which seem not directly related with known active faults on the surface and did not form surface ruptures. Although such individual earthquakes might correspond to a known surface active fault,most of them occurred under active folds,formed by displacement of burial thrusts which are located at depth of tens kilometers beneath the folds. Stein named such earthquake asfolding earthquake. It is quite a challenging issue to study and assess the seismic hazards of folding earthquakes occurring in compressive tectonic regions with active folds and burial thrusts. Derived from active folding secondary faults such as flexural-slip faults,bend-moment faults,it is easier to identify that the fold itself. These secondary faults have coseismic slip at the surface and record the active history of seismogenic thrusts which provide an effective way to study the seismic activity of blind thrusts. Many flexural-slip fault scarps are developed on several terrace surfaces at the two limbs of Mingyaole anticline,located along the western margin of the Tarim Basin. These scarps mainly form on the limb of steep beds closest to active axial surfaces(dips of 74° ~ 89°,18° ~ 20° and 45° ~ 60°,separately),within a range of 50 ~ 1 200m from active axial surface,and most are 90 ~ 1 000m wide. Overall,the height of the flexuralslip fault scarps gradually deceases away from the active axial surface. These scarps occur at nearly equidistant or multiple distance spacing on the same terrace surface. The strike of the flexural-slip fault scarp is consistent with the strike of underlying bedrock,which is dominated by interbedded medium-thick layered sandstone or fine-grain sandstone with similar rock mechanical properties. Since the abandonment of terrace T3 at the south limb of the Mingyaole anticline,the shortening rate and uplift rate absorbed by flexural-slip faults are at least(1. 0 ± 0. 2)mm / a,(1. 2 ± 0. 1)mm / a, respectively. Movement of the flexural-slip faults is characterized by repeatability and neo-activity.
Anticline
Escarpment
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Early Pleistocene
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Reishui-Riyue Mt. active fault zone is a very important NNW oriented rightlateral strikeslip active fault zone which developed in the Chaidam-Qilian Mt. active crustal block,northeastern margin of Qinghai-Tibet Plateau.The activity of the fault causes a series of microgeomorphologies,such as ridge, valley and terrace,rightlateral offseted and forms fault cliff and fault scarp et al. vertical offset microgeomorphology.In this paper,the palaeoearthquake events on the fault are studied.Combining the trench profiles and fault scarp measurement,two palasoearthquake events are determined,which occured in 6 280±120 a B.P. and 2 220±360 a B.P.,the recurrence interval is about 4 000 a.
Terrace (agriculture)
Escarpment
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