Fault-zone Properties and Earthquake Rupture

Fault- geographical zone Properties and Earthquake RuptureINTRODUCTIONGeological structures, specific on the wholey picks play a substantial role in the qualitative and quantitative aspects of hydrogeological processes (Bense, et al., 2006). Fault zones in the earth shallow crust (A first-order description of soil zones commonly includes a fault core, which is surrounded by a damage zone from the hydrogeological perspective. The fault core, as the zone of the most intense strain, is generally found in the common snapping turtle of the fault zone, and identified the most of the displacement within the fault zone. Fault cores in different rocks are commonly zones of fault gouge and breccias (Evans and Chester, 1995 Caine et al., 1996 Evans et al., 1997). The damage zone has secondary structures such as minor faults and fractures extending into the foot wall and hanging wall, which take up the rest of strain within the fault zone (Bense, et al., 2013). The fault core and damage zone are surrounded by protolith that is comparatively undeformed units which may contain joints not primarily related to the fault zone, and exists as a background deformation pattern (Forster and Evans, 1991 Caine and Forster, 1999).The chief(prenominal) hydrogeologic properties of fault zones are believed to be highly anisotropic. Vertical or near-vertical faults are commonly described as being either conduits for horizontal flow on the fault, barricades to horizontal flow across the fault, or a combination of the both respect to the fault core conditions (Anderson and Bakker, 2008).The faulting utensil and motility type is a signifi pilet parameter in the hydrogeological behavior of faults. Normal faults with tension mechanism have a greater ability to groundwater movement and conversely, reverse faults with compressive mechanism, are not proper pathways for groundwater flow. Reverse faults and strike slip faults generated by compression forces, so can act as an impermeable bar rier against groundwater movement across the fault (Goldscheider, 2008).Various fault processes can reduce the permeability of the fault core and cause fault to behave as an impermeable barrier against groundwater flow in unlithified depositorys. Tectonic sediment fuse in fault zones generally leads to a notable reduction of permeability (Faerseth, 2006 Rawling and Goodwin, 2006 Caine and Minor, 2009 Balsamo and Storti, 2011). The physical mixing of sediments with contrasting grain-size distributions can be expected to will in a more poorly sorted sediment mixture than any of the source beds, and for this conclude sediment mixing leads to the efficient reduction of pore space and permeability in the fault zone. The degree to which permeability is reduced as a essence of sediment mixing in unlithified sediments will depend on the contrast in permeability between the end-member beds. Heynekamp et al. (1999) report a reduction in permeability of up to six orders of magnitude as c ompared to the original sand layer, where sandy clay form in the fault zone as a result of mixing between sand and clay layers along the Sand Hill fault zone in New Mexico, USA. The latter engage further illustrates that mixing, from relatively homogeneous source layers, causes strong permeability heterogeneity in the fault zone because of incomplete sediment mixing. In addition to permeability heterogeneity, permeability anisotropy can be expected to be present in fault zones as a result of rotation of bladed sediment grains. Grains aligning preferably with the main fault dip have been observed in both lab-experiments on loose sands, and in naturally faulted sediments ranging from sand to gravel (Bense, et al., 2013). At the grain scale, the increase tortuosity of flow paths across the fault as a result of the realignment of oblate grains in the direction of the fault dip results in permeability anisotropy so that perpendicular to the shear zone, permeability can be up to two orde rs of magnitude lower than along it (Arch and Maltman, 1990).Where clay minerals are present in the sediment matrix, phyllosilicate framework bands will develop along which platy clay minerals orient in the direction of the fault zone andwill so facilitate the sliding of grains historical one another possibly reducing grain breakage (Fossen et al., 2007). Clay smears often develop along fault zones cutting through clay beds. The concentre onclay smear exists mainly because of their potential to efficient block across fault fluid flow (Bense and Van Balen, 2004). Clay smears have been described in stratigraphies characterized by unlithified sediments consisting of sandclay alternations (Yielding et al., 1997).Cataclasis in unlithified sediments is the pervasive brittle fracturing and commination of grains (Engelder, 1974Chester and Logan, 1986 Blenkinsop, 1991Davis and Reynolds, 1996). The effectiveness of cataclasis occurring in unlithified sediments varies as function of grain co mposition, relatively weaker grains such as feldspars can be entirely crushed while stronger quartz grains show low intensity cataclasis characterized by the flaking of grains rather than their entire disintegration by crushing (Loveless et al., 2011 Exner and Tschegg, 2012).Permeability along cataclastic deformation bands in unlithified sediments with clay content is typically reduced more strongly, as compared to undeformed sediments, which is demonstrated by many field and laboratory permeability tests (Antonellini and Aydin, 1994 fisherman and Knipe, 2001). Permeability along cataclastic deformation bands is often anisotropic with the largest reduction in permeability perpendicular to the deformation band (Antonellini and Aydin, 1994 Sigda et al., 1999).Fluids carrying re industrious solutes circulating through fault zones potentially can reduce permeability as a result of waterrock interaction and cementation (Zhang et al., 2008).To determine the influence of the North Tabriz Fault (NTF) on the adjacent groundwater aquifer in Ammand area, the geologic information reported by the Geological Survey of Iran (1996), along with the hydrostratigraphic characteristic of aquifer drives from 57 well logs, were investigated. Well log info employed to correlate the sedimentary layers in order to clarify the type and structure of the region aquifers. Groundwater level and electrical conductivity (EC) of the groundwater samples have been measured in site. Finally, groundwater level isopotential lines along with flow directions and some hydrochemical analysis of 57 water sample were employed to prepare suitable maps which revealed the impact of the fault on the surround aquifer.THE STUDY AREAThe Ammand area is located in the northwest of Iran and in the northwest of Tabriz City (Fig. 1). The Tabriz City is one of the large cities of Iran with more than 1.5 million inhabitants (Moradi, et al. 2011). The study area with 297 mm of average annual precipitation and 12.5oC of average annual temperature has a cold and dry climate according to Emberger classification method. Groundwater of this area as the main source of water supply was exploited for drinking and agriculture purposes. This area was crossed by a large and active fault (North Tabriz Fault) which belongs to the interwoven frame that connects the North Anatolian fault system, located in Turkey, to the Alborz mountain range in Iran and accommodates both the northward motion of Arabia and the westward motion of Anatolia surfaces relative to Eurasia plate (Moradi, et al. 2011).The purpose of this study is to investigate the influence of the North Tabriz fault on the hydrogeological characteristic of the surrounding aquifer.GEOLOGICALSETTINGThe present-day tectonics of Iran is mainly the result of the complex tectonic system due to motion between the Arabian and Eurasia plates (Djamour, et al., 2011). The Tabriz area is part of the complex tectonic system result of the interaction between Arabia, Anatolia and Eurasia plates and comprising the complex system of faults (Sengoret al., 2005 McKenzie, 1972 Jackson, 1992).The North Tabriz Fault (NTF) is the most outstanding tectonic structure in the northwest of Iran with right lateral fault mechanism (Fig. 1). It is one of the most active faults in Iran which has a clear surface expression in most part of its length (Hesami, et al., 2003). It has an average strike of NW-SE over a length of more than 150 km and appears to be generally close to vertical in dip (Vafaei, et al., 2011).Right-lateral movement along this fault, documented by Berberian and Arshadi (1976) from the study of aerial photographs, which in addition can be seen clearly in the field (Karakhanian et al., 2004).NTF lineament in the area is easily recognizable in Miocene units (Fig. 2).Variety of geological formations around the study area according to their rocks composition and the effects of geological phenomena such as North Tabriz fault have contribu ted as the main role in the coming into court of the area current morphology and hydrogeological characteristics of the area aquifers.Geological units of the area are consists of Pliocene gray Dacite in the north, Miocene gypsiferous red marl and sandstone layers that surrounding the area, Quaternary Travertine deposits in central part, which all of these formations have been covered by Quaternary alluvial fan deposits in most part of the area (Fig. 2).