Quantitative Analysis and Visualization of Nonplanar Fault Surfaces Using Terrestrial Laser Scanning (LIDAR)—The Arkitsa Fault, Central Greece, As a Case Study
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Quantitative analysis and visualization of nonplanar fault surfaces using terrestrial laser scanning (LIDAR)—The Arkitsa fault, central Greece, as a case study R.R. Jones* Geospatial Research Ltd., Department of Earth Sciences, University of Durham, Durham DH1 3LE, UK Reactivation Research Group, Department of Earth Sciences, University of Durham, Durham DH1 3LE, UK S. Kokkalas* University of Patras, Department of Geology, Laboratory of Structural Geology, 26500 Patras, Greece K.J.W. McCaffrey* Reactivation Research Group, Department of Earth Sciences, University of Durham, Durham DH1 3LE, UK ABSTRACT variation in surface orientation, with spreads fault reactivation, fault seal, and fl uid fl ow in of ~±20°–25° in strike and ±10° in dip. Most of faulted reservoirs and aquifers. Despite this, most Many fault surfaces are noticeably nonpla- the variation in orientation refl ects decimeter- modeling of fault dynamics assumes idealized nar, often containing irregular asperities and and meter-scale corrugations and longer planar geometries, and no failure criteria have yet more regular corrugations and open warping. wavelength warps of the fault panels. Average been developed for curved faults. Terrestrial laser scanning (light detection and wavelengths of corrugations measured on two One of the main limitations in incorporating ranging, LIDAR) is a powerful and versatile of the panels are 4.04 m and 4.43 m. Whereas realistic fault geometries into dynamic fault mod- tool that is highly suitable for acquisition of the orientations of the three fault surfaces els is the paucity of quantitative studies of three- very detailed, precise measurements of slip- show signifi cant variations, the orientations dimensional geometry of natural fault zones. In surface geometry from well-exposed faults. of fault striae are very similar between the this paper we present detailed data acquired using Quantitative analysis of the LIDAR data, panels, and are tightly clustered within each terrestrial laser scanning (TLS), also known as combined with three- dimensional visualiza- panel. Fault-slip analysis from each panel ground-based LIDAR (light detection and rang- tion software, allows the spatial variation in shows that the local stress fi eld is consistent ing), from well-exposed fault surfaces in an various geometrical properties across the fault with the regional velocity fi eld derived from area of active tectonism, the Aegean. The main surface to be clearly shown. Plotting the varia- global positioning system data. The oblique purpose of this paper is to describe methods to tion in distance of points from the mean fault slip lineations observed on the fault panels process, visualize, and analyze these kinds of plane is an effective way to identify culmina- represent a combination of two contempora- large geospatial data set, including techniques to tions and depressions on the fault surface. neous strain components: north-northeast– highlight spatial variation in different geometric Plots showing the spatial variation of surface south-southwest extension across the Gulf of parameters across a fault surface. orientation are useful in highlighting corru- Evia and sinistral strike slip along the west- gations and warps of different wavelengths, northwest–east- southeast Arkitsa fault zone. REGIONAL SETTING as well as cross faults and fault bifurcations. Analysis of different curvature properties, INTRODUCTION The study site for this work is the area of spec- including normal and Gaussian curvature, tacularly exposed fault surfaces of the Arkitsa provides the best plots for quantitative mea- Many fault surfaces commonly observed in fault zone, reported by Jackson and McKenzie surements of the geometry of corrugations outcrop are markedly nonplanar, and often display (1999), located on the southern side of the north- and folds. However, curvature analysis is corrugations, asperities, and longer wavelength ern Gulf of Evia in central Greece (Fig. 1A). highly scale dependent, so requires careful fi l- low-amplitude curvature. Such irregularities can The area is currently undergoing active north- tering and smoothing of the data to be able to have major effects on the mechanical behavior of south to northeast-southwest regional extension, analyze structures at a given wavelength. the fault during slip, and a better understanding with rates on the order of 1–2 mm/yr (Clarke at Three well-exposed fault panels from the of the interplay between irregular geometry, fault al. 1998), in response to the complex tectonic Arkitsa fault zone in central Greece were kinematics, and dynamics is an important step in interplay between subduction beneath the Hel- scanned and analyzed in detail. Each panel improving our knowledge of a variety of geologi- lenic Arc, backarc extension in the Aegean, and is markedly nonplanar, and shows signifi cant cal processes, including earthquake nucleation, the westward movement of the Anatolian plate *E-mails: Jones: [email protected]; Kokkalas: [email protected]; McCaffrey: [email protected]. Geosphere; December 2009; v. 5; no. 6; p. 465–482; doi: 10.1130/GES00216.1; 10 fi gures; 1 table; 3 animations. For permission to copy, contact [email protected] 465 © 2009 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/5/6/465/3338067/i1553-040X-5-6-465.pdf by guest on 28 September 2021 Jones et al. height A (meters asl) 2500 1000 500 300 39°N 200 Almyr A os-Sperchios e graben g e a 100 Fig.1B n KVF N AK . F ARFZ Gu KF lf 50 Z of E v AT ia F 0 projection: WGS84 S.G ulf of E via Gu lf o f C ori nth 38°N Corinth Athens 22°E 23°E 24°E B 22°55' 23°00' 23°05' Logos Fig. 2 NORTHNORTH 38°45' Ark Arkitsa itsa Fau e lt Zon G u lf o f Livanates A ta Livanates la n Fault ti Megaplatanos 38°40' At Zeli alan Atalanti ti F ault Zone Tragana 10 km 466 Geosphere, December 2009 Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/5/6/465/3338067/i1553-040X-5-6-465.pdf by guest on 28 September 2021 LIDAR analysis and visualization of nonplanar faults at Arkitsa, Greece well constrained. Some historical earthquakes Atalanti fault show similar values, on the order Figure 1. (A) Satellite topography data have been recorded in the area, but none can be of 0.27–0.4 mm/yr (Ganas et al., 1998). In addi- (Shuttle Radar Topography Mission) directly associated with the Arkitsa fault zone, tion to the overview given in Jackson and McK- from central Greece, showing location of or with any other fault with certainty, other enzie (1999), further description was given by the study area on the southern side of the than the 1894 rupture events of Atalanti fault Kokkalas et al. (2007) and Papanikolaou and Gulf of Evia. KVF—Kamena Vourla fault; (Ambraseys and Jackson, 1990). Royden (2007). AKF—Agios Konstantinos fault; ARFZ— The Arkitsa fault zone together with the Agios There is evidence of Holocene seismic activ- Arkitsa fault zone; KFZ—Kallidromo fault Konstantinos and Kamena Vourla faults form a ity along the fault, based on the geomorpho- zone; ATF—Atalanti fault; asl—above sea west-northwest–east-southeast, left- stepping, logical expression of the Arkitsa region, as well level. (B) Tectonic map of the area around north-dipping fault margin that links with the as the back-tilted terraces on the hanging-wall Arkitsa. Fault picks are based on detailed southern margin of the Almyros-Sperchios block of the Arkitsa fault, and the exposure of an aerial photo analysis and ground-truthing. graben (Fig. 1). The Arkitsa fault zone, with ~1-m-high scarp of unweathered fault surface a length of ~10 km, separates Late Triassic– that existed prior to quarrying. In addition, the Jurassic platform carbonates in the footwall coastline in the region shows evidence of Holo- (e.g., Dewey et al., 1986; Doutsos and Kok- from lower Pliocene–Quaternary sediments in cene uplift and subsidence that is controlled by kalas, 2001; Kokkalas et al., 2006). In central the hanging wall. The amount of throw appar- the motion and location of the faults (Roberts Greece, much of the extensional strain is local- ently varies along strike, typical of highly seg- and Jackson, 1991; Stiros et al., 1992). ized into a number of west-northwest– east- mented fault zones. The minimum throw is esti- The Arkitsa fault is best exposed in an out- southeast–trending grabens, which are mostly mated to be ~500–600 m, based on the thickness crop 450 m south of the main Athens-Lamia characterized by complex geometries in map of Neogene–Holocene sediments in the hanging national road (Fig. 2), where recent quarry- view (Fig. 1B), and a high degree of segmen- wall, plus the scarp height and topographic relief ing activity during the past 20 yr has removed tation along strike (Doutsos and Poulimenos, of the footwall block. This allows a slip rate of hanging-wall colluvium to reveal clean, fresh 1992; Ganas et al., 1998; Kokkalas et al., 2006). 0.2–0.3 mm/yr to be estimated for the Arkitsa exposures of the upper 65–70 m of three large Most of the major normal faults in the region are fault zone, given that activity on faults of the fault panels. These fault panels form the north- thought to have been active in the Pleistocene, Evia rift zone started within the past 2–3 m.y. ern scarp edge of a footwall block that rises to although the relative time of their activity is not (Ganas et al., 1998). Slip rates for the adjacent 255 m above sea level (a.s.l.). The hanging-wall Evia n Gulf of Nor ther to L amia Athens oad to National R 500 m Figure 2.