Correction to “Source processes of the 1978 and 2005 Miyagi‐oki, Japan, earthquakes: Repeated rupture of asperities over successive large earthquakes”
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[1] Highly similar seismograms commonly observed along transform or convergent plate boundaries indicate that repeated small to moderate earthquakes occur within a single area. The results of source-process inversions for seismic events within the northeastern Japan subduction zone suggest that large earthquakes and their component asperities also exhibit this repeating nature under certain conditions. However, sets of similar seismograms that might provide direct evidence of the repeated rupture of large-earthquake asperities have not been observed. This paper analyzes two offshore earthquakes near Miyagi Prefecture, Japan, the most recent occurring in 2005 with a JMA magnitude (M) of 7.2 in the source region of the 1978 earthquake (M7.4). We demonstrate the similarity in waveforms from the seismograms recorded during the 1978 and 2005 earthquakes. The early portions of the 2005 seismograms resemble the 1978 seismograms, suggesting that the asperities located close to the 1978 hypocenter ruptured again during the 2005 event. The seismogram similarities provide the first direct evidence for the repeated rupture of asperities during successive large earthquakes. The results of our waveform inversions further indicate that the two asperities of the 2005 event largely coincide with the southern two asperities of the 1978 event. These repeating asperities are recorded in the early portions of the 2005 seismograms with 60% of the amplitude recorded in the 1978 seismograms. The characteristic behavior of the asperities supports the slip-predictable recurrence model of earthquake rupture rather than the time-predictable recurrence model.Accretionary wedge
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Fluvial fans represent one of the dominant sedimentary systems at the active margins of non-marine foreland basins. The Puig-reig anticline at the north-eastern margin of the Ebro Foreland Basin (SE Pyrenees, Spain) exposes continuous outcrops of Late Eocene-Early Oligocene fluvial deposits, from proximal to medial fluvial fan environments. The proximal deposits are found in the north limb of the anticline, especially in the northwest zone. These deposits are characterised by conglomerates with minor interbedded sandstones, with thick and wide sheet-like geometries with unscoured or variably scoured basal surfaces. These are interpreted to be the deposits of unconfined flash floods and wide-shallow channel streams. The medial deposits, covering the rest of the anticline, consist of interbedded conglomerates, sandstones and claystones. These are interpreted to have been deposited from braided to meandering channel streams and overbank areas. Distal deposits are found towards the south, beyond the anticline, and are characterised by sandstone and clay deposits of terminal lobes and lacustrine deltas. This study assesses the impact of the primary depositional characteristics, diagenesis and deformation of the most heterolithic portion of the system, with implications for increasing our understanding of folded fluvial reservoirs. Diagenetic processes, mainly mechanical compaction and calcite cementation, resulted in overall low intergranular porosity, with limited relatively high porosity developed in sandstone lithofacies in the medial deposits. Deformation associated with thrusting and fold growth resulted in the formation of abundant fractures, with relatively high fracture intensities observed in sandstone lithofacies in the anticline crest. This study shows that post-depositional processes can both improve and diminish the reservoir potential of basin proximal fluvial deposits, through the development of fracture networks and by compaction-cementation. The comparison of the Puig-reig anticline with other similar settings worldwide indicates that foreland basin margin locations may be potential areas for effective reservoirs, even in the case of low intergranular porosity.
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Forearc
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Thrust fault
Echelon formation
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Pennsylvanian foreland deformation associated with the Ouachita orogene reactivated a west-northwest-east-southeast Cambrian basement trend, the southern Oklahoma aulacogen, to form the Wichita uplift, southwest Oklahoma. The 30-km-wide subsurface Frontal fault zone separates the uplift from the Anadarko basin to the north. Horizontal shortening across this fault zone is estimated at 7-15 km (20-40%), vertical displacement totals 9-10 km from the uplift to the basin. Folds are mapped on an interformational scale within the Frontal fault zone, and on an intraformational scale (Cambro-Ordovician Arbuckle Group) in the Slick Hills, southwest Oklahoma. Additional shortening occurred along southwest dipping mountain flank thrusts and on bedding plane thrusts, respectively. Hanging wall blocks of major faults contain the shallow dipping limb and anticlinal hinge zone of the interformational scale folds. Oil and gas production is generally restricted to these anticlinal crests within Paleozoic rocks. Deep wells (> 6000 m) that have penetrated footwall imbricates of the mountain flank thrusts have drilled through steep-overturned beds and tight recumbent folds before passing through faults into a normal stratigraphic sequence. Basement thrust loading of the southern margin of the Anadarko basin controlled the trend (west-northwest-east-southeast) of the axis of maximum deposition within the basin during the Pennsylvanian.
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Sediments of Ouachita facies extend subsurface from the Ouachita Mountains of Oklahoma and Arkansas to the Marathon and Solitario uplifts of extreme southwest Texas. Although these sediments have been subjected to strong dynamic metamorphism, the metamorphic grade attained is uniformly low. Sediments of Ouachita facies are essentially unaltered in some areas; elsewhere they range in degree of metamorphism as high as the biotite zone. Mineralogical change and cataclastic effects are key criteria for discerning the stages of progressive metamorphism in sediments of Ouachita facies. Metamorphic changes are most easily observed in shales and argillaceous sandstones--limestones and cherts react less conspicuously to metamorphic stress. Mineralogical change resulting from metamorphism reduces the porosity and non-fracture permeability of sandstones to such an extent that they are not good petroleum reservoirs. The petrography of the so-called schists of Luling field, Caldwell County, Texas, and of some other deep wells along the Luling-Mexia-Talco fault system is discussed briefly. It is shown that they are generally comparable in mineralogy and degree of metamorphism with sediments exposed in the Ouachita Mountains of McCurtain County, Oklahoma. End_of_Article - Last_Page 2626------------
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