Chris Marone

Bio: Chris Marone is an academic researcher from Pennsylvania State University. The author has contributed to research in topics: Slip (materials science) & Fault gouge. The author has an hindex of 60, co-authored 236 publications receiving 14033 citations. Previous affiliations of Chris Marone include Massachusetts Institute of Technology & University of Southern California.

Laboratory-derived friction laws and their application to seismic faulting

Abstract: This paper reviews rock friction and the frictional properties of earthquake faults. The basis for rate- and state-dependent friction laws is reviewed. The friction state variable is discussed, including its interpretation as a measure of average asperity contact time and porosity within granular fault gouge. Data are summarized showing that friction evolves even during truly stationary contact, and the connection between modern friction laws and the concept of “static” friction is discussed. Measurements of frictional healing, as evidenced by increasing static friction during quasistationary contact, are reviewed, as are their implications for fault healing. Shear localization in fault gouge is discussed, and the relationship between microstructures and friction is reviewed. These data indicate differences in the behavior of bare rock surfaces as compared to shear within granular fault gouge that can be attributed to dilation within fault gouge. Physical models for the characteristic friction distance are discussed and related to the problem of scaling this parameter to seismic faults. Earthquake afterslip, its relation to laboratory friction data, and the inverse correlation between afterslip and shallow coseismic slip are discussed in the context of a model for afterslip. Recent observations of the absence of afterslip are predicted by the model.

On the mechanics of earthquake afterslip

Abstract: We propose a model for earthquake afterslip based on rate and state variable friction laws. In the model, afterslip is attributed to the interaction of a velocity-weakening region at depth (within which earthquakes nucleate) with an upper region of velocity-strengthening frictional behavior. The existence of this upper region is supported by independent seismologic observations and the results of laboratory friction experiments. In our model, afterslip is the result of relaxation of a stress perturbation within the velocity-strengthening region, which arises when an earthquake propagates into that region from below. We derive the stress perturbation and its decay from the friction constitutive law using a simple, 1 degree-of-freedom approximation for the elastic interaction between the fault and its surroundings. This approximation is based on thickness-averaged displacements and slip velocities within the velocity-strengthening region, which is assumed to slip as a rigid block. Coseismic and postseismic slip are coupled through the thickness-averaged stiffness k of the velocity-strengthening region. We assume k to be inversely proportional to the thickness of this region, which means that thicker velocity strengthening regions have a greater tendency to arrest coseismic slip. We model the afterslip-time histories of the 1966 Parkfield and 1987 Superstition Hills earthquakes and relate the model parameters to physical parameters which may govern the rheologic behavior of the faults. In accord with field observations, our model predicts (1) that afterslip on some faults scales with the thickness of the (unconsolidated) sedimentary cover and (2) that proportionally more afterslip occurs for earthquakes in which coseismic surface slip is small compared with coseismic slip at depth. Velocity-strengthening frictional behavior is to be expected for faults within poorly consolidated sediments and for those that contain significant gouge zones (about >500 m) within their shallow regions (<3–5 km). Combining our results with those of recent laboratory friction studies indicates that relatively young faults with little accumulated fault gouge should exhibit little afterslip.

Frictional behavior and constitutive modeling of simulated fault gouge

Abstract: This paper presents an investigation of the factional properties and stability of frictional sliding for simulated fault gouge. In these experiments we sheared gouge layers (quartz sand) under saturated drained conditions and at constant normal stress (50–190 MPa) between either rough steel surfaces or Westerly granite surfaces in a triaxial apparatus. Surface roughness (60 to 320 grit) and gouge layer thickness (0–4.0 mm) were varied in the experiments with granite samples. Porosity ϕ was monitored continuously during shear. Our measurements indicate that granular gouge exhibits strain hardening and net compaction for shear strains γ less than 0.5–1.0. For γ > 0.5–1.0, sliding occurs at approximately constant shear stress and net compaction from one load/unload cycle to the next ceases. Dilatancy occurs at 1/3 to 1/2 the shear stress required for sliding and d2ϕ/dγ2 becomes negative at about the peak stress in a given loading cycle, indicating the onset of shear localization. Oblique shear bands appear in the layers at γ = 1.3–1.5. Experiments with an initial gouge layer exhibit velocity strengthening (the coefficient of friction increases with slip velocity), and initially bare granite surfaces exhibit velocity weakening. The magnitude of velocity strengthening varies inversely with normal stress and directly with gouge thickness and surface roughness. In the gouge experiments the dilatancy rate dϕ/dγ also varies with slip rate. Using a simple energy balance to relate volume change and frictional resistance, we find quantitative agreement between the measured change in dilatancy rate and friction following changes in slip rate. This indicates that velocity strengthening within granular gouge is the result of dilatancy. The slip rate dependence of dϕ/dγ increases with gouge thickness and surface roughness, in agreement with the friction data. Our data therefore suggest that slip within unconsolidated granular material, such as some natural fault gouges, is inherently stable. The results thus provide an explanation for (1) the tendency of gouge accumulation to stabilize slip in laboratory samples, and (2) the tendency for aseismic slip within shallow (< 3–5 km) unconsolidated fault gouge and within unconsolidated sediments such as shallow alluvium and accretionary prisms.

Fault zone fabric and fault weakness

Abstract: Geological and geophysical evidence suggests that some crustal faults are weak compared to laboratory measurements of frictional strength. Explanations for fault weakness include the presence of weak minerals, high fluid pressures within the fault core and dynamic processes such as normal stress reduction, acoustic fluidization or extreme weakening at high slip velocity. Dynamic weakening mechanisms can explain some observations; however, creep and aseismic slip are thought to occur on weak faults, and quasi-static weakening mechanisms are required to initiate frictional slip on mis-oriented faults, at high angles to the tectonic stress field. Moreover, the maintenance of high fluid pressures requires specialized conditions and weak mineral phases are not present in sufficient abundance to satisfy weak fault models, so weak faults remain largely unexplained. Here we provide laboratory evidence for a brittle, frictional weakening mechanism based on common fault zone fabrics. We report on the frictional strength of intact fault rocks sheared in their in situ geometry. Samples with well-developed foliation are extremely weak compared to their powdered equivalents. Micro- and nano-structural studies show that frictional sliding occurs along very fine-grained foliations composed of phyllosilicates (talc and smectite). When the same rocks are powdered, frictional strength is high, consistent with cataclastic processes. Our data show that fault weakness can occur in cases where weak mineral phases constitute only a small percentage of the total fault rock and that low friction results from slip on a network of weak phyllosilicate-rich surfaces that define the rock fabric. The widespread documentation of foliated fault rocks along mature faults in different tectonic settings and from many different protoliths suggests that this mechanism could be a viable explanation for fault weakening in the brittle crust.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

The Mechanics of Earthquakes and Faulting

Abstract: This essential reference for graduate students and researchers provides a unified treatment of earthquakes and faulting as two aspects of brittle tectonics at different timescales. The intimate connection between the two is manifested in their scaling laws and populations, which evolve from fracture growth and interactions between fractures. The connection between faults and the seismicity generated is governed by the rate and state dependent friction laws - producing distinctive seismic styles of faulting and a gamut of earthquake phenomena including aftershocks, afterslip, earthquake triggering, and slow slip events. The third edition of this classic treatise presents a wealth of new topics and new observations. These include slow earthquake phenomena; friction of phyllosilicates, and at high sliding velocities; fault structures; relative roles of strong and seismogenic versus weak and creeping faults; dynamic triggering of earthquakes; oceanic earthquakes; megathrust earthquakes in subduction zones; deep earthquakes; and new observations of earthquake precursory phenomena.

A Double-Difference Earthquake Location Algorithm: Method and Application to the Northern Hayward Fault, California

Abstract: We have developed an efficient method to determine high-resolution hypocenter locations over large distances. The location method incorporates ordinary absolute travel-time measurements and/or cross-correlation P-and S-wave differential travel-time measurements. Residuals between observed and theoretical travel-time differences (or double-differences) are minimized for pairs of earthquakes at each station while linking together all observed event-station pairs. A least-squares solu- tion is found by iteratively adjusting the vector difference between hypocentral pairs. The double-difference algorithm minimizes errors due to unmodeled velocity struc- ture without the use of station corrections. Because catalog and cross-correlation data are combined into one system of equations, interevent distances within multiplets are determined to the accuracy of the cross-correlation data, while the relative lo- cations between multiplets and uncorrelated events are simultaneously determined to the accuracy of the absolute travel-time data. Statistical resampling methods are used to estimate data accuracy and location errors. Uncertainties in double-difference locations are improved by more than an order of magnitude compared to catalog locations. The algorithm is tested, and its performance is demonstrated on two clus- ters of earthquakes located on the northern Hayward fault, California. There it col- lapses the diffuse catalog locations into sharp images of seismicity and reveals hor- izontal lineations of hypocenters that define the narrow regions on the fault where stress is released by brittle failure.

Earthquakes and friction laws

Abstract: The traditional view of tectonics is that the lithosphere comprises a strong brittle layer overlying a weak ductile layer, which gives rise to two forms of deformation: brittle fracture, accompanied by earth- quakes, in the upper layer, and aseismic ductile flow in the layer beneath Although this view is not incorrect, it is imprecise, and in ways that can lead to serious misunderstandings The term ductility, for example, can apply equally to two common rock deformation mechanisms: crystal plasticity, which occurs in rock above a critical temperature, and cataclastic flow, a type of granular deformation which can occur in poorly consolidated sediments Although both exhibit ductility, these two deformation mechanisms have very different rheologies Earthquakes, in turn, are associated with strength and brittleness—associations that are likewise sufficiently imprecise that, if taken much beyond the generality implied in the opening sentence, they can lead to serious misinterpretations about earthquake mechanics Lately, a newer, much more precise and predictive model for the earthquake mechanism has emerged, which has its roots in the observation that tectonic earthquakes seldom if ever occur by the sudden appearance and propagation of a new shear crack (or 'fault') Instead, they occur by sudden slippage along a pre-existing fault or plate interface They are therefore a frictional, rather than fracture, phenomenon, with brittle fracture playing a secondary role in the lengthening of faults 1 and frictional wear 2 This distinction was noted by several early workers 3 , but it was not until 1966 that Brace and Byerlee 4 pointed out that earthquakes must be the result of a stick-slip frictional instability Thus, the earthquake is the 'slip', and the 'stick' is the interseismic period of elastic strain accumula- tion Subsequently, a complete constitutive law for rock friction has been developed based on laboratory studies A surprising result is that a great many other aspects of earthquake phenomena also now seem to result from the nature of the friction on faults The properties traditionally thought to control these processes— strength, brittleness and ductility—are subsumed within the over- arching concept of frictional stability regimes Constitutive law of rock friction In the standard model of stick-slip friction it is assumed that sliding begins when the ratio of shear to normal stress on the surface reaches a value ms, the static friction coefficient Once sliding initiates, frictional resistance falls to a lower dynamic friction coefficient, md, and this weakening of sliding resistance may,

Laboratory-derived friction laws and their application to seismic faulting

Abstract: This paper reviews rock friction and the frictional properties of earthquake faults. The basis for rate- and state-dependent friction laws is reviewed. The friction state variable is discussed, including its interpretation as a measure of average asperity contact time and porosity within granular fault gouge. Data are summarized showing that friction evolves even during truly stationary contact, and the connection between modern friction laws and the concept of “static” friction is discussed. Measurements of frictional healing, as evidenced by increasing static friction during quasistationary contact, are reviewed, as are their implications for fault healing. Shear localization in fault gouge is discussed, and the relationship between microstructures and friction is reviewed. These data indicate differences in the behavior of bare rock surfaces as compared to shear within granular fault gouge that can be attributed to dilation within fault gouge. Physical models for the characteristic friction distance are discussed and related to the problem of scaling this parameter to seismic faults. Earthquake afterslip, its relation to laboratory friction data, and the inverse correlation between afterslip and shallow coseismic slip are discussed in the context of a model for afterslip. Recent observations of the absence of afterslip are predicted by the model.