Segmentation along Strike-Slip Faults Revisited

Fault segmentation and fault steps and their evolution are relevant to the dynamics and size of earthquake ruptures, the distribution of fault damage zones and the capacity of fault seal. Furthermore, segment interactions and coalescence are the fundamental processes for fault growth. To contribute to this end, we investigated the architecture of strike-slip faults by combining field observations in the Valley of Fire State Park, Nevada, and the published data sets. First, we studied the trace complexity for 49 faults with offsets ranging from 12 m to 460 km. We established that the number of fault steps (hence fault segments) per unit length is correlated to the maximum fault offset by a negative power law. The faults have longer segments and fewer steps when their offsets increase, indicating the progressive growth, smoothening and simplification of the fault traces as a function of the offset, as proposed by previous investigators. Second, we studied the dimensions of the segments and steps composing ~20 of the previous fault systems. The mean segment length, mean step length and mean step width are all correlated to the maximum fault offset by positive power laws over four orders of magnitude of the offset. In addition, the segment length distributions of four of the faults with offsets ranging from 80 m to 100 km are all lognormal, with most of the segment lengths falling in the range of one to five times the maximum offset of the faults. Finally, the fault steps have an approximately constant length-to-width ratio indicating that, regardless of their environment, strike-slip faults have a remarkable self-similar architecture probably due to the mechanical processes responsible for fault growth. Our data sets can be used as tools to better predict the geometrical attributes of strike-slip fault systems with important consequences for earthquake ruptures, the distribution and properties of fault damage zones, and fault sealing potential.     

Failure modes of the lineaments on Jupiter's moon, Europa: Implications for the evolution of its icy crust

Lineaments referred to as ridges, troughs, bands, and faults on the icy surface of Jupiter's moon, Europa, have long been interpreted as extensional structures due to brittle fracturing of ice and intrusion of mobile materials from the interior of the satellite. Based on detailed mapping and possibly analogous structures present on Earth, we propose that the kinematics and failure mechanisms of these structures are variable and more complex than previously thought. A dense network of structures of multiple generations, forming the background on the surface of the planet, is here interpreted as localized zones of volumetric strain, likely compaction and/or dilation bands. The next class of linear failure structures is shear bands with significant offset of pre-existing markers. A few additional phases of less pervasive but more prominent volumetric deformation bands overprint the shear zones and background network. The mode of younger features can be characterized as sharp, dilational, brittle fracturing and subsequent shearing, thereby producing comminution and fragmentation in various sizes, leading to a series of younger faults with detectable lateral, as well as vertical, offset. This rich variability in the nature of the distribution, localization, kinematics, and formation mechanisms, if true, suggests that the conditions prevailing within the crust of Europa must have changed dramatically over time. The implication of this conclusion is that structures interpreted to be compaction/dilation bands and shear bands on Europa are composed of deformed materials similar to the surrounding ice, whereas only the younger faults, developed by brittle fracturing and fragmentation, may be conduits for mobile substrate to reach the surface and thus offer the highest potential for recovering evidence for life in the satellite.     

Permeability upscaling of fault zones in the Aztec Sandstone,Valley of Fire State Park,Nevada, with a focus on slip surfaces and slip bands

The effect of open and filled slip surfaces on the upscaled permeability of two fault zones with 6 and 14 m strike-slip in an eolian Aztec Sandstone, Nevada, USA is evaluated. Each fault zone is composed of several fault components: a fault core, bounded by filled through-going slip surfaces referred to as slip bands, and a surrounding damage zone that contains joints and deformation bands. Slip band geometry, composition, and petrophysical properties are characterized. Measurements and modeling show that slip band permeabilities can vary over 12 orders of magnitude depending on the degree of fill within the slip bands. The slip bands along with other fault zone components are represented in finite volume numerical calculations and the impact of various slip-band representations on upscaled fault zone permeability is tested. The results show 2 orders of magnitude variation in upscaled fault zone permeability in the fault-normal direction and a factor of 2 variation in the fault-parallel direction. The numerical results presented here are compared to the earlier numerical results in which structured Cartesian grids were used for the numerical simulations, and are in qualitative agreement with earlier calculations but use about a factor of 250–400 fewer numerical cells.     

Evaluation of parameters affecting earthquake damage by decision tree techniques

Earthquake damages are assessed based on a holistic approach using structural as well as non-structural factors to model earthquake damage distributions with Decision Tree Techniques, using the Answer Tree program and the damage data from recent major earthquakes in Turkey. The damage dataset consists of approximately 9,400 buildings that were surveyed to evaluate the factors affecting building damage after Erzincan [1992], Dinar [1995], and Kocaeli [1999] earthquakes. The earthquake damage is defined as the dependent variable, while earthquake magnitude (M), intensity (I) in the city, peak ground acceleration (PGA) in each city, epicenter distance (ED), building types (BT), number of storeys (NS), presence of soft storey (SS), building position (BP) on the site, and site conditions (SC) are independent variables in the proposed model. The damage level (DL) was classified with respect to red, yellow, and green codes. The main purpose was (1) to identify the factors controlling building damage during earthquakes; (b) to determine the most significant factor; (c) to evaluate the effects of different factors for different earthquakes; (d) to develop damage distribution models for different subgroups based on the Decision Tree Techniques.

Quasi‐static analysis of elastic behavior for some systems having higher fracture densities

Elastic behavior of geomechanical systems with interacting (but not intersecting) fractures is treated using generalizations of the Backus and the Schoenberg–Muir methods for analyzing layered systems whose layers are intrinsically anisotropic due to locally aligned fractures. By permitting the axis of symmetry of the locally anisotropic compliance matrix for individual layers to differ from that of the layering direction, we derive analytical formulas for interacting fractured regions with arbitrary orientations to each other. This procedure provides a systematic tool for studying how contiguous, but not yet intersecting, fractured domains interact, and provides a direct (though approximate) means of predicting when and how such interactions lead to more dramatic weakening effects and ultimately to failure of these complicated systems. The method permits decomposition of the system elastic behavior into specific eigenmodes that can all be analyzed, and provides a better understanding about which of these specific modes are expected to be most important to the evolving failure process. Copyright © 2009 John Wiley & Sons, Ltd.     

Soil liquefaction susceptibility and hazard mapping in the residential area of Kütahya (Turkey)

This study presents the results of both field and laboratory tests that have been undertaken to assess liquefaction susceptibilities of the soils in Kütahya city, located in the well-known seismically active fault zone. Liquefaction potentials of the sub-surface materials at Kütahya city were estimated by using the geological aspect and geotechnical methods such as SPT method of field testing. And, the data obtained have been mapped according to susceptibility and hazard. The susceptibility map indicated “liquefable” and “marginally liquefable” areas in alluvium, and “non-liquefable” areas in Neogene unit for the magnitude of earthquake of M=6.5; whereas, liquefaction hazard map produced by using of liquefaction potential index showed the severity categories from “very low” to “high.” However, a large area in the study area is prone to liquefy according to liquefaction susceptibility map; the large parts of the liquefable horizon are mapped as “low” class of severity by the use of the liquefaction potential index. It can be said that hazard mapping of liquefaction for a given site is crucial than producing liquefaction susceptibility map for estimating the severity. Both the susceptibility and hazard maps should be produced and correlated with each other for planning in an engineering point of view.     

Probabilistic evaluation of observed earthquake damage data in Turkey

Empirical, theoretical or hybrid methods can be used for the vulnerability analysis of structures to evaluate the seismic damage data and to obtain probability damage matrices. The information on observed structural damage after earthquakes has critical importance to drive empirical vulnerability methods. The purpose of this paper is to evaluate the damage distributions based on the data observed in Erzincan-1992, Dinar-1995 and Kocaeli-1999 earthquakes in Turkey utilizing two probability models—Modified Binomial Distribution (MBiD) and Modified Beta Distribution (MBeD). Based on these analyses, it was possible (a) to compare the advantages and limitations of the two probability models with respect to their capabilities in modelling the observed damage distributions; (b) to evaluate the damage assessment for reinforced concrete and masonry buildings in Turkey based on these models; (c) to model the damage distribution of different sub-groups such as buildings with different number of storeys or soil conditions according to the both models. The results indicate that (a) MBeD is more suitable than the MBiD to model the observed damage data for both reinforced concrete and masonry buildings in Turkey; (b) the sub-groups with lower number of stories are located in the lower intensity levels, while the sub-groups with higher number of stories depending on local site condition are concentrated in the higher intensity levels, thus site conditions should also be considered in the assessment of the intensity levels; (c) the detailed local models decrease the uncertainties of loss estimation since the damage distribution of sub-groups can be more accurately modelled compared to the general damage distribution models.     

Interaction of multiple cracks and formation of echelon crack arrays

Fracturing of rock under compression is a product of a series of processes, including nucleation, growth, interaction and coalescence of multiple microcracks. The formation of echelon arrays of microcracks and macrocracks is one of the crucial rings in the processes. We use a superposition and asymptotic approximation technique to analyse the interaction of multiple cracks with various geometrical configurations. It is shown that crack geometry has a strong influence on crack interaction. Echelon crack arrays produce the strongest interaction and are the preferred geometrical configuration for multiple cracks prior to the formation of through-going shear fractures. This technique provides parameter-dependent global behaviour, and is more efficient and easier to use.     

Use of joint-growth directions and rock textures to infer thermal regimes during solidification of basaltic lava flows

Thermal contraction joints form in the upper and lower solidifying crusts of basaltic lava flows and grow toward the interior as the crusts thicken. Lava flows are thus divided by vertical joints that, by changes in joint spacing and form, define horizontal intraflow layers known as tiers. Entablatures are tiers with joint spacings less than about 40 cm, whereas colonnades have larger joint spacings. We use structural and petrographic methods to infer heat-transfer processes and to constrain environmental conditions that produce these contrasting tiers. Joint-surface morphology indicates overall joint-growth direction and thus identifies the level in a flow where the upper and lower crusts met. Rock texture provides information on relative cooling rates in the tiers of a flow. Lava flows without entablature have textures that develop by relatively slow cooling, and two joint sets that usually meet near their middles, which indicate mostly conductive cooling. Entablature-bearing flows have two main joint sets that meet well below their middles, and textures that indicate fast cooling of entablatures and slow cooling of colonnades. Entablatures always occur in the upper joint sets and sometimes alternate several times with colonnades. Solidification times of entablature-bearing flows, constrained by lower joint-set thicknesses, are much less than those predicted by a purely conductive cooling model. These results are best explained by a cooling model based on conductive heat transfer near a flow base and water-steam convection in the upper part of an entablature-bearing flow. Calculated solidification rates in the upper parts of such flows exceed that of the upper crust of Kilauea Iki lava lake, where water-steam convection is documented. Use of the solidification rates in an available model of water-steam convection yields permeability values that agree with measured values for fractured crystalline rock. We conclude, therefore, that an entablature forms when part of a flow cools very rapidly by water-steam convection. Flooding of the flow top by surface drainage most likely induces the convection. Colonnades form under conditions of slower cooling by conductive heat transfer in the absence of water.