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_Journal of Structural Geology 32 (2010) 1305–1316_ _Contents lists available at ScienceDirect_ _Journal of Structural Geology_ _journal homepage: www.elsevier.com/locate/jsg_ _Inferred fluid flow through fault damage zones based on the observation of stalactites in carbonate caves_ _Young-Seog Kim a,*, David J. Sanderson b_ _a Department of Environmental Geosciences, Pukyong National University, Busan 608-737, Republic of Korea_ _b School of Civil Engineering and the Environment, University of Southampton, SO17 1BJ, UK_ _article info_ _Article history: Received 3 December 2007; Received in revised form 5 January 2009; Accepted 9 April 2009; Available online 12 May 2009_ _Keywords: Fault damage zones Fluid flow Limestone cave Stalactites Fractured reservoirs_ _abstract_ _Faults and fractures are important factors that control fluid flow in rock masses in hydrothermal, groundwater, and hydrocarbon systems. In this paper we examine local variations in fluid flow as evidenced by the distribution patterns and sizes of stalactites in fractured limestone. We observe that the size and distribution of stalactites relate to fluid flow and is strongly controlled by the fracture apertures, intersection of fractures, and development of damage zones around a fault._ _Fault damage zones are the volumes of deformed wall rocks around a fault surface that result from the initiation, propagation, interaction, termination, and build-up of slip along the fault. They are divided into tip-, wall-, and linkage damage zones depending on their location along the fault. The pattern of deformation within a damage zone mainly depends on fault tip modes (mode II or III), the 3-D locations around a fault surface, and the evolutionary stage of the fault. The development of different structures within damage zones gives valuable information about fault initiation and termination, fault propagation and growth, and fluid flow._ _Stalactites indicate fluid flow variation within a fault in that fluid flow is high in dilational jogs, variable along the main fault traces, and low in contractional jogs. Variation in ore fluid flow within faults is also important in controlling the position of ore shoots in structurally-controlled hydrothermal mineral deposits. Thus, the characteristics of fluid flow in fractured carbonate rocks can be related to patterns of damage around faults. Hence, the mapping of damage zones can be applied to the study of fracture-controlled fluid flow in the fields of petroleum geology, hydrogeology, and ore deposits._ _© 2009 Elsevier Ltd. All rights reserved._ _1. Introduction_ _Faults and fractures are important in controlling fluid flow in many groundwater and hydrocarbon reservoirs. The specific reaction of the reservoirs to deformation depends on the amount and direction of displacement, the response of wall rocks, and the nature of the rock in the fault zone. Simple fractures (or joints) can influence the porosity and permeability of the rock. The opening of fractures due to deformation leads to both enhancement and localization of fluid flow (e.g., Zhang and Sanderson, 1998, 2001). The widespread development of veins associated with faulting and other forms of deformation attest to past periods of enhanced fluid flow (e.g., Micarelli and Benedicto, 2008). Slip on fractures leads to faults and may produce further localized fracturing (or damage) of the wall rocks (e.g., Kim et al., 2000). The porosity and permeability of the wall rocks may increase due to increased fracture density and or dilatancy associated with shear on fractures, or may be reduced by the juxtaposition of rocks with differing permeability and the development of fault gouge (e.g., Yielding et al., 1997; Agosta, 2008). Although opening and slip may be viewed as end members, a range of kinematics are developed in faults and fracture zones, with bends and jogs being particularly important in the development of damage and increase of fluid permeability._ _We use the term damage to describe any type of deformation that is spatially and kinematically associated with a fault or shear zone (e.g., McGrath and Davison, 1995; Kim et al., 2003, 2004; Myers and Aydin, 2004). The term fault damage zone has been used with two slightly different meanings in structural geology. One usage is for the highly deformed zone outside the fault core (e.g., Shipton and Cowie, 2001, 2003; Billi et al., 2003; Odling et al., 2004; Agosta, 2008), whereas the other usage is for the zone of secondary structures developed around faults to accommodate displacement along the fault, especially at fault tips and oversteps (e.g., McGrath and Davison, 1995; Kim et al., 2003, 2004; Flodin and Aydin, 2004; Zhang et al., 2008). In this paper, we mainly use the term with the latter meaning, although wall damage may include aspects of the former._ _1306_ _Y.-S. Kim, D.J. Sanderson Journal of Structural Geology 32 (2010) 1305–1316_ _Distributed damage_ _Linkage damage_ _Wall damage_ _Tip damage_ _Fig. 1. Classification of damage zones based on location around a segmented fault. Distributed damage is scattered extensional fracturing that is formed in the same stress field but prior to the development of the main fault. Tip damage is developed in response to stress concentrations and to accommodate changing displacement at the fault tip. Wall damage is developed as propagation of tip damage and kinematic damage with accumulating displacement. Linkage damage is developed by overprinting of old tips and linking process._ _Recent 3-D conceptual damage models around faults (Kim et al., 2003, 2004) provide a basis for the prediction of damage patterns. Fault damage zones are classified into distributed damage, tip damage, wall damage, and linkage damage based on the location of fractures around a segmented master fault (Fig. 1; Kim et al., 2004). Damage zones around faults (e.g., McGrath and Davison, 1995; Kim et al., 2003, 2004; Myers and Aydin, 2004) are good targets for exploration of many resources such as groundwater, hydrocarbons, or hydrothermal ore minerals (Li et al., 2001; Micklethwaite and Cox, 2004; Cox and Ruming, 2004; Leckenby et al., 2005; Zhang et al., 2008)._ _In this paper, we examine the relationship between the density and aperture of fractures and the resulting hydraulic conductance (e.g., Leckenby et al., 2005) or effects of fluid flow (Micklethwaite and Cox, 2004; Cox and Ruming, 2004) based on stalactite distributions in several limestone caves. In particular, the relative amount of fluid flow is quantified in an example of stalactite development in a Korean limestone cave and is related to the location of damage zones around faults._ _2. Classification of fault damage_ _A variety of damage patterns is observed around faults. For simplicity, we will describe mainly those from strike-slip faults. The basic concept of the damage classification and damage patterns is the same for all faults (Kim et al., 2004)._ _Four types of damage are recognized around a segmented fault (Fig. 1) and can be distinguished based on the location and characteristics of secondary fractures developed in damage zones. The terminology is essentially non-genetic; each of the four categories can result from a range of processes related to the development of the fault, and can be interpreted in terms of the kinematics and dynamics of the fault tip mode and wall rock evolution._ _Tip damage (Fig. 1) is developed at the tip of a fault. It is easily recognized, and has been widely reported in the literature (e.g., Segall and Pollard, 1983; Granier, 1985; Pollard and Segall, 1987; McGrath and Davison, 1995; Kim et al., 2003; Micarelli and Benedicto, 2008). This type of damage is developed as a result of stress concentrations and or to accommodate rapid changes in displacement developed at the fault tip. Tip damage is similar to the process zone associated with fracture propagation in crystalline materials, and has been extended to large-scale seismogenic faults (e.g., King, 1986), where it plays an important role in the nucleation and termination of earthquake ruptures. Tip damage has been classified by Kim et al. (2004), and may be easily extended to large-scale faults (e.g., Storti et al., 2003; Kim and Sanderson, 2006). Areas of tensile failure at fault tips are also described from numerical modeling studies (e.g., Bourne and Willemse, 2001; Zhang et al., 2008)._ _Wall damage occurs where fracturing is distributed within the wall rocks surrounding the fault (Fig. 1), with the degree of fracturing generally decreasing away from the main fault. Various types of wall damage have been recognized that develop by different processes associated with fault growth, and these may be difficult to distinguish. Wall damage is classified into three main categories, including those that form as a result of (a) mode II tip propagation (i.e., sequential development of tip damage), (b) the intersection of the mode III tips of faults, and (c) increasing strain in the wall rocks due to drag associated with slip on the fault (kinematic damage)._ _Linkage damage (Fig. 1) represents a high intensity of fractures developed between overstepping fault segments (Martel et al., 1988; Peacock and Sanderson, 1991, 1995; Myers and Aydin, 2004). The linkage damage may develop by overprinting of old tip damage zones, or be induced by strain during the evolution of the overstepping fault segments to accommodate accumulating displacement. Linkage damage is classified into two main categories – dilational and contractional jogs, depending on the sense of stepping in relation to the fault displacement and, hence, the stress conditions in the relay._ Ключевые слова: e, r, o