A three-step maximum a posteriori probability method for InSAR data inversion of coseismic rupture with application to the 14 April 2010 Mw 6.9 Yushu, China, earthquake

NASA Astrophysics Data System (ADS)

Sun, Jianbao; Shen, Zheng-Kang; Bürgmann, Roland; Wang, Min; Chen, Lichun; Xu, Xiwei

2013-08-01

develop a three-step maximum a posteriori probability method for coseismic rupture inversion, which aims at maximizing the a posterior probability density function (PDF) of elastic deformation solutions of earthquake rupture. The method originates from the fully Bayesian inversion and mixed linear-nonlinear Bayesian inversion methods and shares the same posterior PDF with them, while overcoming difficulties with convergence when large numbers of low-quality data are used and greatly improving the convergence rate using optimization procedures. A highly efficient global optimization algorithm, adaptive simulated annealing, is used to search for the maximum of a posterior PDF ("mode" in statistics) in the first step. The second step inversion approaches the "true" solution further using the Monte Carlo inversion technique with positivity constraints, with all parameters obtained from the first step as the initial solution. Then slip artifacts are eliminated from slip models in the third step using the same procedure of the second step, with fixed fault geometry parameters. We first design a fault model with 45° dip angle and oblique slip, and produce corresponding synthetic interferometric synthetic aperture radar (InSAR) data sets to validate the reliability and efficiency of the new method. We then apply this method to InSAR data inversion for the coseismic slip distribution of the 14 April 2010 Mw 6.9 Yushu, China earthquake. Our preferred slip model is composed of three segments with most of the slip occurring within 15 km depth and the maximum slip reaches 1.38 m at the surface. The seismic moment released is estimated to be 2.32e+19 Nm, consistent with the seismic estimate of 2.50e+19 Nm.

49 CFR 571.126 - Standard No. 126; Electronic stability control systems.

Code of Federal Regulations, 2011 CFR

2011-10-01

... series uses counterclockwise steering, and the other series uses clockwise steering. The maximum time... rate and to estimate its side slip or side slip derivative with respect to time; (4) That has a means... after completion of the sine with dwell steering input (time T0 + 1 in Figure 1) must not exceed 35...

Very shallow source of the October 2010 Mentawai tsunami earthquake from tsunami field data and high-rate GPS

NASA Astrophysics Data System (ADS)

Hill, E. M.; Qiu, Q.; Borrero, J. C.; Huang, Z.; Banerjee, P.; Elosegui, P.; Fritz, H. M.; Macpherson, K. A.; Li, L.; Sieh, K. E.

2011-12-01

"Tsunami earthquakes," which produce very large tsunamis compared to those expected from their magnitude, have long puzzled geoscientists, in part because only a handful have occurred within the time of modern instrumentation. The Mw 7.8 Mentawai earthquake of 25 October 2010, which occurred seaward of the southern Mentawai islands of Sumatra, was such an event. This earthquake triggered a very large tsunami, causing substantial damage and 509 casualties. Detailed field surveys we conducted immediately after the earthquake reveal maximum runup in excess of 16 m. The Sumatra GPS Array (SuGAr) recorded beautiful 1-sec data for this event at sites on the nearby islands, making this the first tsunami earthquake to be recorded by a dense, high-rate, and proximal GPS network, and giving us a unique opportunity to study these rare events from a new perspective. We estimate a maximum horizontal coseismic GPS displacement of 22 cm, at a site ~50 km from the epicenter. Vertical displacements show subsidence of the islands, but are on the order of only a few cm. Comparison of coseismic offsets from 1-sec and 24-hr GPS solutions indicates that rapid afterslip following the earthquake amounts to ~30% of the displacement estimated by the 24-hr solutions. The coseismic displacements are smaller than expected, and an unconstrained inversion of the GPS displacements indicates maximum fault slip of ~90 cm. Slip of this magnitude will produce maximum seafloor uplift of <15 cm, which is clearly not enough to produce tsunami runup of 16 m. However, investigation of the model resolution from GPS indicates that we are limited in our ability to resolve slip very close to the trench. We therefore deduce that to obtain the adequate level of slip and seafloor uplift to trigger the tsunami, the rupture must have occurred outside the resolution of the GPS network, i.e., at very shallow depths close to the trench. We therefore place prior slip constraints on the GPS inversion, based on preferred values from tsunami modeling of the field data. In the constrained inversion, the small GPS displacements force any slip close to the islands back down to much lower values than the a priori estimates, leaving only a very narrow and shallow strip of high slip close to the trench. In this presentation we will show several possible models that include slip on either the megathrust itself or a shallow splay fault, with maximum slip of ~7 m and ~4 m, respectively. This very shallow slip raises questions about the seismic hazard potential of a region of the fault that is often considered to be aseismic. Particularly, these results suggest that when model resolution is not adequate for making determinations of the updip limit of the seismogenic zone of subduction faults, it may be best to assume that it extends all the way to the trench.

Effects of slip, slip rate, and shear heating on the friction of granite

USGS Publications Warehouse

Blanpied, M.L.; Tullis, T.E.; Weeks, J.D.

1998-01-01

The stability of fault slip is sensitive to the way in which frictional strength responds to changes in slip rate and in particular to the effective velocity dependence of steady state friction ????ss/?? ln V. This quantity can vary substantially with displacement, temperature and slip rate. To investigate the physical basis for this behavior and the possible influence of shear heating, we slid initially bare granite surfaces in unconfined rotary shear to displacements of hundreds of millimeters at normal stresses, ??n, of 10 and 25 MPa and at room temperature. We imposed step changes in slip rate within the range 10-2 to 103.5 ??m/s and also monitored frictional heating with thermistors embedded in the granite. The transient response of ?? to slip rate steps was fit to a rate- and state-dependent friction law using two state variables to estimate the values of several parameters in the constitutive law. The first 20 mm of slip shows rising friction and falling ????ss/?? ln V; further slip shows roughly constant friction, ????ss/?? ln V and parameter values, suggesting that a steady state condition is reached on the fault surface. At V ??? 10 ??m/s, ????ss/?? ln V = -0.004 ?? 0.001. At higher rates the response is sensitive to normal stress: At ??n = 25 MPa granite shows a transition to effective velocity strengthening (????ss/?? ln V = 0.008 ?? 0.004) at the highest slip rates tested. At 10 MPa granite shows a less dramatic change to ????ss/?? ln V ??? 0 at the highest rates. The maximum temperature measured in the granite is ???60??C at 25 MPa and 103.5 ??m/s. Temperatures are in general agreement with a numerical model of heat conduction which assumes spatially homogeneous frictional heating over the sliding surface. The simplest interpretation of our measurements of ????ss/?? ln V is that the granite is inherently veocity weakening (?????ss/??? In V 0 mimics velocity strengthening. These results have implications for the frictional behavior of faults during earthquakes. High slip rates may cause a switch to effective velocity strengthening which could limit peak coseismic slip rate and stress drop. For fluid-saturated faults, strengthening by this mechanism may be partly or fully offset by weakening due to thermal pressurization of a poorly drained pore fluid.

Analysis of mean seismic ground motion and its uncertainty based on the UCERF3 geologic slip rate model with uncertainty for California

USGS Publications Warehouse

Zeng, Yuehua

2018-01-01

The Uniform California Earthquake Rupture Forecast v.3 (UCERF3) model (Field et al., 2014) considers epistemic uncertainty in fault‐slip rate via the inclusion of multiple rate models based on geologic and/or geodetic data. However, these slip rates are commonly clustered about their mean value and do not reflect the broader distribution of possible rates and associated probabilities. Here, we consider both a double‐truncated 2σ Gaussian and a boxcar distribution of slip rates and use a Monte Carlo simulation to sample the entire range of the distribution for California fault‐slip rates. We compute the seismic hazard following the methodology and logic‐tree branch weights applied to the 2014 national seismic hazard model (NSHM) for the western U.S. region (Petersen et al., 2014, 2015). By applying a new approach developed in this study to the probabilistic seismic hazard analysis (PSHA) using precomputed rates of exceedance from each fault as a Green’s function, we reduce the computer time by about 10^5‐fold and apply it to the mean PSHA estimates with 1000 Monte Carlo samples of fault‐slip rates to compare with results calculated using only the mean or preferred slip rates. The difference in the mean probabilistic peak ground motion corresponding to a 2% in 50‐yr probability of exceedance is less than 1% on average over all of California for both the Gaussian and boxcar probability distributions for slip‐rate uncertainty but reaches about 18% in areas near faults compared with that calculated using the mean or preferred slip rates. The average uncertainties in 1σ peak ground‐motion level are 5.5% and 7.3% of the mean with the relative maximum uncertainties of 53% and 63% for the Gaussian and boxcar probability density function (PDF), respectively.

Spectrum of Slip Processes on the Subduction Interface in a Continuum Framework Resolved by Rate-and State Dependent Friction and Adaptive Time Stepping

NASA Astrophysics Data System (ADS)

Herrendoerfer, R.; van Dinther, Y.; Gerya, T.

2015-12-01

To explore the relationships between subduction dynamics and the megathrust earthquake potential, we have recently developed a numerical model that bridges the gap between processes on geodynamic and earthquake cycle time scales. In a self-consistent, continuum-based framework including a visco-elasto-plastic constitutive relationship, cycles of megathrust earthquake-like ruptures were simulated through a purely slip rate-dependent friction, albeit with very low slip rates (van Dinther et al., JGR, 2013). In addition to much faster earthquakes, a range of aseismic slip processes operate at different time scales in nature. These aseismic processes likely accommodate a considerable amount of the plate convergence and are thus relevant in order to estimate the long-term seismic coupling and related hazard in subduction zones. To simulate and resolve this wide spectrum of slip processes, we innovatively implemented rate-and state dependent friction (RSF) and an adaptive time-stepping into our continuum framework. The RSF formulation, in contrast to our previous friction formulation, takes the dependency of frictional strength on a state variable into account. It thereby allows for continuous plastic yielding inside rate-weakening regions, which leads to aseismic slip. In contrast to the conventional RSF formulation, we relate slip velocities to strain rates and use an invariant formulation. Thus we do not require the a priori definition of infinitely thin, planar faults in a homogeneous elastic medium. With this new implementation of RSF, we succeed to produce consistent cycles of frictional instabilities. By changing the frictional parameter a, b, and the characteristic slip distance, we observe a transition from stable sliding to stick-slip behaviour. This transition is in general agreement with predictions from theoretical estimates of the nucleation size, thereby to first order validating our implementation. By incorporating adaptive time-stepping based on a fraction of characteristic slip distance over maximum slip velocity, we are able to resolve stick-slip events and increase computational speed. In this better resolved framework, we examine the role of aseismic slip on the megathrust cycle and its dependence on subduction velocity.

Late Pleistocene-Holocene Activity of the Strike-slip Xianshuihe Fault Zone, Tibetan Plateau, Inferred from Tectonic Landforms

NASA Astrophysics Data System (ADS)

Lin, A.; Yan, B.

2017-12-01

Knowledges on the activity of the strike-slip fault zones on the Tibetan Plateau have been promoted greatly by the interpretation of remote sensing images (Molnar and Tapponnier, 1975; Tapponnier and Molnar, 1977). The active strike-slip Xianshuihe-Xiaojiang Fault System (XXFS), with the geometry of an arc projecting northeastwards, plays an important role in the crustal deformation of the Tibetan Plateau caused by the continental collision between the Indian and Eurasian plates. The Xianshuihe Fault Zone (XFZ) is located in the central segment of the XXFS and extends for 370 km, with a maximum sinistral offset of 60 km since 13‒5 Ma. In this study, we investigated the tectonic landforms and slip rate along the central segment of the left-lateral strike-slip XFZ. Field investigations and analysis of ttectonic landforms show that horizontal offset has been accumulated on the topographical markers of different scales that developed since the Last Glacial Maximum (LGM). The central segment of the XFZ is composed of three major faults: Yalahe, Selaha, and Zheduotang faults showing a right-stepping echelon pattern, that is characterized by systematical offset of drainages, alluvial fans and terrace risers with typical scissoring structures, indicating a structural feature of left-lateral strike-slip fault. Based on the offset glacial morphology and radiocarbon dating ages, we estimate the Late Pleistocene-Holocene slip rate to be 10 mm/yr for the central segment of the XFZ, which is consistent with that estimated from the GPS observations and geological evidence as reported previously. Across the central segment of the XFZ, the major Selaha and Zheduotang faults participate a slip rate of 5.8 mm/yr and 3.4 mm/yr, respectively. Detailed investigations of tectonic landforms are essential for the understanding the activity of active faults. Our findings suggest that the left-lateral slipping of the XFZ partitions the deformation of eastward extrusion and northeastward shortening of the central Tibetan Plateau to accommodate the continuing penetration of the Indian plate into the Eurasian plate.

An experimental study of the influence of stress history on fault slip during injection of supercritical CO2

NASA Astrophysics Data System (ADS)

Cuss, Robert J.; Wiseall, Andrew C.; Tamayo-Mas, Elena; Harrington, Jon F.

2018-04-01

The injection of super-critical CO2 into a depleted reservoir will alter the pore pressure of the basin, which if sufficiently perturbed could result in fault slip. Therefore, knowledge of the acceptable pressure limits is required in order to maintain fault stability. A two-part laboratory study was conducted on fully saturated kaolinite fault gouge to investigate this issue. Previously, we showed that fault slip occurred once pore-pressure within the gouge was sufficient to overcome the normal stress acting on the fault. For kaolinite, this behaviour occurred at a pressure similar to the yield stress. The current study shows that following a slow-reduction in the maximum principal stress, as would be expected through changes in effective stress, the reactivation pressure shows a stress memory. Consequently, the pressure necessary to initiate fault slip is similar to that required at the maximum stress encountered. Therefore, fault slip is at least partially controlled by the previous maximum stress and not the current stress state. During the slow reduction in normal stress, the flow characteristics of the fault remain unchanged until pore-pressure exceeds shear stress and does not increase significantly until it exceeds normal stress. This results in fault slip, which slows the rate of flow increase as shear is an effective self-sealing mechanism. These observations lead to the conclusion that stress history is a vital parameter when considering fault stability.

Late quaternary slip-rate variations along the Warm Springs Valley fault system, northern Walker Lane, California-Nevada border

USGS Publications Warehouse

Gold, Ryan; dePolo, Craig; Briggs, Richard W.; Crone, Anthony

2013-01-01

The extent to which faults exhibit temporally varying slip rates has important consequences for models of fault mechanics and probabilistic seismic hazard. Here, we explore the temporal behavior of the dextral‐slip Warm Springs Valley fault system, which is part of a network of closely spaced (10–20 km) faults in the northern Walker Lane (California–Nevada border). We develop a late Quaternary slip record for the fault using Quaternary mapping and high‐resolution topographic data from airborne Light Distance and Ranging (LiDAR). The faulted Fort Sage alluvial fan (40.06° N, 119.99° W) is dextrally displaced 98+42/-43 m, and we estimate the age of the alluvial fan to be 41.4+10.0/-4.8 to 55.7±9.2  ka, based on a terrestrial cosmogenic 10Be depth profile and 36Cl analyses on basalt boulders, respectively. The displacement and age constraints for the fan yield a slip rate of 1.8 +0.8/-0.8 mm/yr to 2.4 +1.2/-1.1 mm/yr (2σ) along the northern Warm Springs Valley fault system for the past 41.4–55.7 ka. In contrast to this longer‐term slip rate, shorelines associated with the Sehoo highstand of Lake Lahontan (~15.8  ka) adjacent to the Fort Sage fan are dextrally faulted at most 3 m, which limits a maximum post‐15.8 ka slip rate to 0.2  mm/yr. These relations indicate that the post‐Lahontan slip rate on the fault is only about one‐tenth the longer‐term (41–56 ka) average slip rate. This apparent slip‐rate variation may be related to co‐dependent interaction with the nearby Honey Lake fault system, which shows evidence of an accelerated period of mid‐Holocene earthquakes.

Spatio-temporal Evolution of On-going Tokai Slow Thrust Slip Event, Central Japan

NASA Astrophysics Data System (ADS)

Miyazaki, S.; Segall, P.; Kato, T.; McGuire, J.; Hatanaka, Y.

2003-12-01

We investigate an on-going slow thrust slip event that occurred at a subduction zone along the Nankai Trough off central Japan. The area we investimate, referred as the Tokai seismic gap, is located to the east of the 1944 Tonankai earthquake, which did not slip in the 1944 event. Continuous GPS data from April 1996 to the end of 1999 shows that the stations in this region have secular velocities of ˜ 2 cm/yr to the northwest relative to the landward plate. The GPS time series show an abrupt increase in rate in late June, 2000. The accelerated rate is currently on-going. We model this non-secular deformation, which we refer to the 2000 Tokai slow slip event, by transient slip at the plate interface and estimate their distribution with Kalman Filter based inversion methods. This event initiated around (137.3oE, 34.9oN) almost at the same time of the onset of volcanic activity on Miyake-jima in late June, 2000. This suggests that the 2000 Tokai slow slip event is triggered by the volcanic activity on Miyake-jima. Then the locus of the slip propagated to (137.5oE, 34.75oN) in second half of 2000, and kept slipping at the maximum rate of ˜ 15cm/yr through 2001. The peak slip-rate propagated to around (137.75oE, 34.9oN) in early 2002. The depth of slip zone is ˜ 25km, which may correspond to the lower edge of the seismogenic zone for the anticipated Tokai earthquake defined from seismicity. The cumulative moment magnitude of the slow slip event to date is MW ˜ 6.8. The duration of this event is longer than previously studied slow slip events using GPS data, including the 1996 Bungo slow slip event (about 1 year) and the 1996 and the 2000 Boso slow events (a few weeks).

Insights into the causal relationship between slow slip and tectonic tremor in Guerrero, Mexico

NASA Astrophysics Data System (ADS)

Villafuerte, Carlos; Cruz-Atienza, Víctor M.

2017-08-01

Similar to other subduction zones, tectonic tremors (TTs) and slow-slip events (SSEs) take place in the deep segment of the plate interface in Guerrero, Mexico. However, their spatial correlation in this region is not as clear as the episodic tremor and slip observed in Cascadia and Japan. In this study we provide insights into the causal relationship between TTs and SSEs in Guerrero by analyzing the evolution of the deformation fields induced by the long-term 2006 SSE together with new locations of TTs and low-frequency earthquakes (LFEs). Unlike previous studies we find that the SSE slip rate modulates the TT and LFE activity in the whole tremor region. This means that the causal relationship between the SSE and the TT activity directly depends on the stressing rate history of the tremor asperities that is modulated by the surrounding slip rate. We estimated that the frictional strength of the asperities producing tremor downdip in the sweet spot is around 3.2 kPa, which is 2.3 times smaller than the corresponding value updip in the transient zone, partly explaining the overwhelming tremor activity of the sweet spot despite that the slow slip there is smaller. Based on the LFE occurrence-rate history during the interlong-term SSE period, we determined that the short-term SSEs in Guerrero take place further downdip (about 35 km) than previously estimated, with maximum slip of about 8 mm in the sweet spot. This new model features a continuum of slow slip extending across the entire tremor region of Guerrero.

Estimation of slip distribution using an inverse method based on spectral decomposition of Green's function utilizing Global Positioning System (GPS) data

NASA Astrophysics Data System (ADS)

Jin, Honglin; Kato, Teruyuki; Hori, Muneo

2007-07-01

An inverse method based on the spectral decomposition of the Green's function was employed for estimating a slip distribution. We conducted numerical simulations along the Philippine Sea plate (PH) boundary in southwest Japan using this method to examine how to determine the essential parameters which are the number of deformation function modes and their coefficients. Japanese GPS Earth Observation Network (GEONET) Global Positioning System (GPS) data were used for three years covering 1997-1999 to estimate interseismic back slip distribution in this region. The estimated maximum back slip rate is about 7 cm/yr, which is consistent with the Philippine Sea plate convergence rate. Areas of strong coupling are confined between depths of 10 and 30 km and three areas of strong coupling were delineated. These results are consistent with other studies that have estimated locations of coupling distribution.

Uplift of the Kenai Peninsula, Alaska, since the 1964 Prince William Sound earthquake

NASA Technical Reports Server (NTRS)

Cohen, Steven; Holdahl, Sandford; Caprette, Douglas; Hilla, Stephen; Safford, Robert; Schultz, Donald

1995-01-01

Using Global Positioning System (GPS) receivers, we reoccupied several leveling benchmarks on the Kenai Peninsula of Alaska which had been surveyed by conventional leveling immediately following the March 27, 1964, Prince William Sound earthquake (M(sub w) = 9.3). By combining the two sets of measurements with a new, high-resolution model of the geoid in the region, we were able to determine the cumulative 1993-1964 postseismic vertical displacement. We find uplift at all of our benchmarks, relative to Seward, Alaska, a point that is stable according to tide gauge data. The maximum uplift of about 1 m occurs near the middle of the peninsula. The region of maximum uplift appears to be shifted northwest relative to the point of maximum coseismic subsidence. If we use tide gauge data at Nikishka and Seward to constrain the vertical motion, then the observed uplift has a trenchward tilt (down to the southeast) as well as an arching component. To explain the observations, we use creep-at-depth models. Most acceptable models require a fault slip of about 2.75 m, although this result is not unique. If the slip has been continuous since the 1964 earthquake, then the average slip rate is nearly 100 mm/yr, twice the plate convergence rate. Comparing the net uplift achieved in 29 years with that observed over 11 years in an adjacent region southeast of Anchorage, Alaska, we conclude that the rate of uplift is decreasing. A further decrease in the uplift rate is expected as the 29-year averaged displacement rate is about twice the plate convergence rate and therefore cannot be sustained over the entire earthquake cycle.

Strength variation along the Altyn Tagh and the Kunlun fault, northern Tibetan plateau, inferred from 3D mechanical modeling

NASA Astrophysics Data System (ADS)

Zhu, X.; He, J.; Xiao, J.

2017-12-01

The Altyn Tagh (ATF) and the Kunlun (KLF) fault distribute around the northern Tibetan plateau from west to east about 2000 km and 1200 km in length, and deform predominately with left-lateral strike-slip motion. Previous geological and geodetic observations suggested that over at least 800-km length of the faults, the slip rate averaged on active deformation period is quite uniform, for the ATF being about 9-10 mm/yr and the KLF about 10-12mm/yr. Strike-slip deformation of these faults is undoubtedly result from regional loading by ongoing collision between the India and the Eurasia continent. Whereas, dense GPS measurements show that along the central Tibetan plateau from west to east, the GPS velocity field changes greatly both on magnitude and on direction, suggesting that tectonic loading to the ATF and the KLF could be changed along their strike directions. To investigate how a non-uniform tectonic loading condition as documented by the GPS velocity field could cause a relatively uniform slip rate of the two active faults, we built a three-dimensional viscoelastic finite element model, in which motion of the strike-slip fault is governed by frictional strength. Given a reasonable bound of model parameters, we at first test the numerical calculation with uniform frictional coefficient of the faults. At this condition, the predicted slip rate is inevitably largest near center of the faults and gradually decreasing to the fault ends. To better fitting the observed uniform slip rate along the faults over 1000km length, variation of fault strength along the ATF and the KLF must be invoked. By testing numerous models, an optimum result was obtained, among which the frictional coefficient for the ATF is varied from 0.02 to 0.12 between 820E and 1000E with its maximum at 840E, and for the KLF from 0.02 to 0.10 with its maximum between 950E and 970E. This means that the strength of the two large-scale strike-slip faults exists significant difference along their strikes. We believe that the predicted fault pattern could play an important role on partitioning strain aside the fault, together on determination of potential rupture during an earthquake.

Geophysical Signatures of Shear-Induced Damage and Frictional Processes on Rock Joints

NASA Astrophysics Data System (ADS)

Hedayat, Ahmadreza; Haeri, Hadi; Hinton, John; Masoumi, Hossein; Spagnoli, Giovanni

2018-02-01

In this study, ultrasonic waves recorded during direct shear experiments on rock joints were employed to investigate the shear failure processes. Three types of wave attributes were systematically observed prior to the shear failure of the rock joints: (a) maximum in the amplitude of the transmitted wave, (b) maximum in the dominant frequency of the transmitted wave, and (c) maximum in the velocity of the wave. Different processes occurring during both frictional sliding and stick-slip oscillations were identified in this study: (a) interseismic phase and (b) preseismic phase. The interseismic phase is associated with elastic loading, very small local slip rate, and increasing ultrasonic transmission along the contact surfaces. The rock joint is considered locked, and the increase in ultrasonic transmission represents an increase in the real (true) area of contact because of interlocking and contact aging. The start of the preseismic phase is marked by the onset of precursors for different regions of the rock joint. Following the interseismic and preseismic phases, coseismic phase occurs. The coseismic phase begins with the reduction in the applied shear stress and is associated with an abrupt increase in the local slip rate. The reductions in transmitted amplitude, wave velocity, and dominant frequency all indicate the preseismic phase when the asperity contacts begin to fail before macroscopic frictional sliding. The observation of the preseismic phase in both the loading phase leading to stable sliding and stick-slip failure modes suggests that microphysical processes of fault weakening may share key features for these two failure modes.

Slip rates on San Francisco Bay area faults from anelastic deformation of the continental lithosphere

USGS Publications Warehouse

Geist, E.L.; Andrews, D.J.

2000-01-01

Long-term slip rates on major faults in the San Francisco Bay area are predicted by modeling the anelastic deformation of the continental lithosphere in response to regional relative plate motion. The model developed by Bird and Kong [1994] is used to simulate lithospheric deformation according to a Coulomb frictional rheology of the upper crust and a dislocation creep rheology at depth. The focus of this study is the long-term motion of faults in a region extending from the creeping section of the San Andreas fault to the south up to the latitude of Cape Mendocino to the north. Boundary conditions are specified by the relative motion between the Pacific plate and the Sierra Nevada - Great Valley microplate [Argus and Gordon, 2000]. Rheologic-frictional parameters are specified as independent variables, and prediction errors are calculated with respect to geologic estimates of slip rates and maximum compressive stress directions. The model that best explains the region-wide observations is one in which the coefficient of friction on all of the major faults is less than 0.15, with the coefficient of friction for the San Andreas fault being approximately 0.09, consistent with previous inferences of San Andreas fault friction. Prediction error increases with lower fault friction on the San Andreas, indicating a lower bound of ??SAF > 0.08. Discrepancies with respect to previous slip rate estimates include a higher than expected slip rate along the peninsula segment of the San Andreas fault and a slightly lower than expected slip rate along the San Gregorio fault.

Rupture dynamics along bimaterial interfaces: a parametric study of the coupling between interfacial sliding and normal traction perturbation

NASA Astrophysics Data System (ADS)

Scala, Antonio; Festa, Gaetano; Vilotte, Jean-Pierre

2017-04-01

Earthquake ruptures often develop along faults separating materials with dissimilar elastic properties. Due to the broken symmetry, the propagation of the rupture along the bimaterial interface is driven by the coupling between interfacial sliding and normal traction perturbations. We numerically investigate in-plane rupture growth along a planar interface, under slip weakening friction, separating two dissimilar isotropic linearly elastic half-spaces. We perform a parametric study of the classical Prakash-Clifton regularisation for different material contrasts. In particular mesh-dependence and regularisation-dependence of the numerical solutions are analysed in this parameter space. When regularisation involves a slip-rate dependent relaxation time, a characteristic sliding distance is identified below which numerical solutions no longer depend on the regularisation parameter, i.e. they are consistent solutions of the same physical problem. Such regularisation provides an adaptive high-frequency filter of the slip-induced normal traction perturbations, following the dynamic shrinking of the dissipation zone during the acceleration phase. In contrast, regularisation involving a constant relaxation time leads to numerical solutions that always depend on the regularisation parameter since it fails adapting to the shrinking of the process zone. Dynamic regularisation is further investigated using a non-local regularisation based on a relaxation time that depends on the dynamic length of the dissipation zone. Such reformulation is shown to provide similar results as the dynamic time scale regularisation proposed by Prakash-Clifton when slip rate is replaced by the maximum slip rate along the sliding interface. This leads to the identification of a dissipative length scale associated with the coupling between interfacial sliding and normal traction perturbations, together with a scaling law between the maximum slip rate and the dynamic size of the process zone during the rupture propagation. Dynamic time scale regularisation is show to provide mesh-independent and physically well-posed numerical solutions during the acceleration phase toward an asymptotic speed. When generalised Rayleigh wave does not exist, numerical solutions are shown to tend toward an asymptotic velocity higher than the slowest shear wave speed. When generalised Rayleigh wave speed exists, as numerical solutions tend toward this velocity, increasing spurious oscillations develop and solutions become unstable. In this regime regularisation dependent and unstable finite-size pulses may be generated. This instability is associated with the singular behaviour of the slip-induced normal traction perturbations, and of the slip rate at the rupture front, in relation with complete shrinking of the dissipation zone. This phase requires to be modelled either by more complex interface constitutive laws involving velocity-strengthening effects that may stabilize short wavelength interfacial propagating modes or by considering non-ideal interfaces that introduce a new length scale in the problem that may promote selection and stabilization of the slip pulses.

Afterslip behavior following the M6.0, 2014 South Napa earthquake with implications for afterslip forecasting on other seismogenic faults

USGS Publications Warehouse

Lienkaemper, James J.; DeLong, Stephen B.; Domrose, Carolyn J; Rosa, Carla M.

2016-01-01

The M6.0, 24 Aug. 2014 South Napa, California, earthquake exhibited unusually large slip for a California strike-slip event of its size with a maximum coseismic surface slip of 40-50 cm in the north section of the 15 km-long rupture. Although only minor (<10 cm) surface slip occurred coseismically in the southern 9-km section of the rupture, there was considerable postseismic slip, so that the maximum total slip one year after the event approached 40-50 cm, about equal to the coseismic maximum in the north. We measured the accumulation of postseismic surface slip on four, ~100-m-long alignment arrays for one year following the event. Because prolonged afterslip can delay reconstruction of fault-damaged buildings and infrastructure, we analyzed its gradual decay to estimate when significant afterslip would likely end. This forecasting of Napa afterslip suggests how we might approach the scientific and engineering challenges of afterslip from a much larger M~7 earthquake anticipated on the nearby, urban Hayward Fault. However, we expect its afterslip to last much longer than one year.The M6.0, 24 Aug. 2014 South Napa, California, earthquake exhibited unusually large slip for a California strike-slip event of its size with a maximum coseismic surface slip of 40-50 cm in the north section of the 15 km-long rupture. Although only minor (<10 cm) surface slip occurred coseismically in the southern 9-km section of the rupture, there was considerable postseismic slip, so that the maximum total slip one year after the event approached 40-50 cm, about equal to the coseismic maximum in the north. We measured the accumulation of postseismic surface slip on four, ~100-m-long alignment arrays for one year following the event. Because prolonged afterslip can delay reconstruction of fault-damaged buildings and infrastructure, we analyzed its gradual decay to estimate when significant afterslip would likely end. This forecasting of Napa afterslip suggests how we might approach the scientific and engineering challenges of afterslip from a much larger M~7 earthquake anticipated on the nearby, urban Hayward Fault. However, we expect its afterslip to last much longer than one year.

Foreshock sequences and short-term earthquake predictability on East Pacific Rise transform faults.

PubMed

McGuire, Jeffrey J; Boettcher, Margaret S; Jordan, Thomas H

2005-03-24

East Pacific Rise transform faults are characterized by high slip rates (more than ten centimetres a year), predominantly aseismic slip and maximum earthquake magnitudes of about 6.5. Using recordings from a hydroacoustic array deployed by the National Oceanic and Atmospheric Administration, we show here that East Pacific Rise transform faults also have a low number of aftershocks and high foreshock rates compared to continental strike-slip faults. The high ratio of foreshocks to aftershocks implies that such transform-fault seismicity cannot be explained by seismic triggering models in which there is no fundamental distinction between foreshocks, mainshocks and aftershocks. The foreshock sequences on East Pacific Rise transform faults can be used to predict (retrospectively) earthquakes of magnitude 5.4 or greater, in narrow spatial and temporal windows and with a high probability gain. The predictability of such transform earthquakes is consistent with a model in which slow slip transients trigger earthquakes, enrich their low-frequency radiation and accommodate much of the aseismic plate motion.

Crustal strain near the Big Bend of the San Andreas Fault: Analysis of the Los Padres-Tehachapi Trilateration Networks, California

NASA Astrophysics Data System (ADS)

Eberhart-Phillips, Donna; Lisowski, Michael; Zoback, Mark D.

1990-02-01

In the region of the Los Padres-Tehachapi geodetic network, the San Andreas fault (SAF) changes its orientation by over 30° from N40°W, close to that predicted by plate motion for a transform boundary, to N73°W. The strain orientation near the SAF is consistent with right-lateral shear along the fault, with maximum shear rate of 0.38±0.01 μrad/yr at N63°W. In contrast, away from the SAF the strain orientations on both sides of the fault are consistent with the plate motion direction, with maximum shear rate of 0.19±0.01 μrad/yr at N44°W. The strain rate does not drop off rapidly away from the fault, and thus the area is fit by either a broad shear zone below the SAF or a single fault with a relatively deep locking depth. The fit to the line length data is poor for locking depth d less than 25 km. For d of 25 km a buried slip rate of 30 ± 6 mm/yr is estimated. We also estimated buried slip for models that included the Garlock and Big Pine faults, in addition to the SAF. Slip rates on other faults are poorly constrained by the Los Padres-Tehachapi network. The best fitting Garlock fault model had computed left-lateral slip rate of 11±2 mm/yr below 10 km. Buried left-lateral slip of 15±6 mm/yr on the Big Pine fault, within the Western Transverse Ranges, provides significant reduction in line length residuals; however, deformation there may be more complicated than a single vertical fault. A subhorizontal detachment on the southern side of the SAF cannot be well constrained by these data. We investigated the location of the SAF and found that a vertical fault below the surface trace fits the data much better than either a dipping fault or a fault zone located south of the surface trace.

Slip triggered on southern California faults by the 1992 Joshua Tree, Landers, and big bear earthquakes

USGS Publications Warehouse

Bodin, Paul; Bilham, Roger; Behr, Jeff; Gomberg, Joan; Hudnut, Kenneth W.

1994-01-01

Five out of six functioning creepmeters on southern California faults recorded slip triggered at the time of some or all of the three largest events of the 1992 Landers earthquake sequence. Digital creep data indicate that dextral slip was triggered within 1 min of each mainshock and that maximum slip velocities occurred 2 to 3 min later. The duration of triggered slip events ranged from a few hours to several weeks. We note that triggered slip occurs commonly on faults that exhibit fault creep. To account for the observation that slip can be triggered repeatedly on a fault, we propose that the amplitude of triggered slip may be proportional to the depth of slip in the creep event and to the available near-surface tectonic strain that would otherwise eventually be released as fault creep. We advance the notion that seismic surface waves, perhaps amplified by sediments, generate transient local conditions that favor the release of tectonic strain to varying depths. Synthetic strain seismograms are presented that suggest increased pore pressure during periods of fault-normal contraction may be responsible for triggered slip, since maximum dextral shear strain transients correspond to times of maximum fault-normal contraction.

Factors controlling high-frequency radiation from extended ruptures

NASA Astrophysics Data System (ADS)

Beresnev, Igor A.

2017-09-01

Small-scale slip heterogeneity or variations in rupture velocity on the fault plane are often invoked to explain the high-frequency radiation from earthquakes. This view has no theoretical basis, which follows, for example, from the representation integral of elasticity, an exact solution for the radiated wave field. The Fourier transform, applied to the integral, shows that the seismic spectrum is fully controlled by that of the source time function, while the distribution of final slip and rupture acceleration/deceleration only contribute to directivity. This inference is corroborated by the precise numerical computation of the full radiated field from the representation integral. We compare calculated radiation from four finite-fault models: (1) uniform slip function with low slip velocity, (2) slip function spatially modulated by a sinusoidal function, (3) slip function spatially modulated by a sinusoidal function with random roughness added, and (4) uniform slip function with high slip velocity. The addition of "asperities," both regular and irregular, does not cause any systematic increase in the spectral level of high-frequency radiation, except for the creation of maxima due to constructive interference. On the other hand, an increase in the maximum rate of slip on the fault leads to highly amplified high frequencies, in accordance with the prediction on the basis of a simple point-source treatment of the fault. Hence, computations show that the temporal rate of slip, not the spatial heterogeneity on faults, is the predominant factor forming the high-frequency radiation and thus controlling the velocity and acceleration of the resulting ground motions.

Production of nanoparticles during experimental deformation of smectite and implications for seismic slip

NASA Astrophysics Data System (ADS)

Aretusini, S.; Mittempergher, S.; Plümper, O.; Spagnuolo, E.; Gualtieri, A. F.; Di Toro, G.

2017-04-01

Nanoparticles and amorphous materials are common constituents of the shallow sections of active faults. Understanding the conditions at which nanoparticles are produced and their effects on friction can further improve our understanding of fault mechanics and earthquake energy budgets. Here we present the results of 59 rotary shear experiments conducted at room humidity conditions on gouge consisting of mixtures of smectite (Ca-montmorillonite) and quartz. Experiments with 60, 50, 25, 0 wt.% Ca-montmorillonite, were performed to investigate the influence of variable clay content on nanoparticle production and their influence on frictional processes. All experiments were performed at a normal stress of 5 MPa, slip rate of 0.0003 ≤ V ≤ 1.5 ms-1, and at a displacement of 3 m. To monitor the development of fabric and the mineralogical changes during the experiments, we investigated the deformed gouges using scanning and transmission electron microscopy combined with X-ray powder diffraction quantitative phase analysis. This integrated analytical approach reveals that, at all slip rates and compositions, the nanoparticles (grain size of 10-50 nm) are partly amorphous and result from cataclasis, wear and mechanical solid-state amorphization of smectite. The maximum production of amorphous nanoparticle occurs in the intermediate slip rate range (0.0003 ≤ V ≤ 0.1 ms-1), at the highest frictional work, and is associated to diffuse deformation and slip strengthening behavior. Instead, the lowest production of amorphous nanoparticles occurs at co-seismic slip rates (V ≥ 1.3 ms-1), at the highest frictional power and is associated with strain and heat localization and slip weakening behavior. Our findings suggest that, independently of the amount of smectite nanoparticles, they produce fault weakening only when typical co-seismic slip rates (>0.1 ms-1) are achieved. This implies that estimates of the fracture surface energy dissipated during earthquakes in natural faults might be extremely difficult to constrain.

Universal behavior in ideal slip

NASA Technical Reports Server (NTRS)

Bozzolo, Guillermo; Ferrante, John; Smith, John R.

1991-01-01

The slip energies and stresses are computed for defect-free crystals of Ni, Cu, Ag, and Al using the many-atom approach. A simple analytical expression for the slip energies is obtained, leading to a universal form for slip, with the energy scaled by the surface energy and displacement scaled by the lattice constant. Maximum stresses are found to be somewhat larger than but comparable with experimentally determined maximum whisker strengths.

From Geodetic Imaging of Seismic and Aseismic Fault Slip to Dynamic Modeling of the Seismic Cycle

NASA Astrophysics Data System (ADS)

Avouac, Jean-Philippe

2015-05-01

Understanding the partitioning of seismic and aseismic fault slip is central to seismotectonics as it ultimately determines the seismic potential of faults. Thanks to advances in tectonic geodesy, it is now possible to develop kinematic models of the spatiotemporal evolution of slip over the seismic cycle and to determine the budget of seismic and aseismic slip. Studies of subduction zones and continental faults have shown that aseismic creep is common and sometimes prevalent within the seismogenic depth range. Interseismic coupling is generally observed to be spatially heterogeneous, defining locked patches of stress accumulation, to be released in future earthquakes or aseismic transients, surrounded by creeping areas. Clay-rich tectonites, high temperature, and elevated pore-fluid pressure seem to be key factors promoting aseismic creep. The generally logarithmic time evolution of afterslip is a distinctive feature of creeping faults that suggests a logarithmic dependency of fault friction on slip rate, as observed in laboratory friction experiments. Most faults can be considered to be paved with interlaced patches where the friction law is either rate-strengthening, inhibiting seismic rupture propagation, or rate-weakening, allowing for earthquake nucleation. The rate-weakening patches act as asperities on which stress builds up in the interseismic period; they might rupture collectively in a variety of ways. The pattern of interseismic coupling can help constrain the return period of the maximum- magnitude earthquake based on the requirement that seismic and aseismic slip sum to match long-term slip. Dynamic models of the seismic cycle based on this conceptual model can be tuned to reproduce geodetic and seismological observations. The promise and pitfalls of using such models to assess seismic hazard are discussed.

Cosmogenic 10Be and 36Cl geochronology of offset alluvial fans along the northern Death Valley fault zone: Implications for transient strain in the eastern California shear zone

USGS Publications Warehouse

Frankel, K.L.; Brantley, K.S.; Dolan, J.F.; Finkel, R.C.; Klinger, R.E.; Knott, J.R.; Machette, M.N.; Owen, L.A.; Phillips, F.M.; Slate, J.L.; Wernicke, B.P.

2007-01-01

The northern Death Valley fault zone (NDVFZ) has long been recognized as a major right-lateral strike-slip fault in the eastern California shear zone (ECSZ). However, its geologic slip rate has been difficult to determine. Using high-resolution digital topographic imagery and terrestrial cosmogenic nuclide dating, we present the first geochronologically determined slip rate for the NDVFZ. Our study focuses on the Red Wall Canyon alluvial fan, which exposes clean dextral offsets of seven channels. Analysis of airborne laser swath mapping data indicates ???297 ?? 9 m of right-lateral displacement on the fault system since the late Pleistocene. In situ terrestrial cosmogenic 10Be and 36C1 geochronology was used to date the Red Wall Canyon fan and a second, correlative fan also cut by the fault. Beryllium 10 dates from large cobbles and boulders provide a maximum age of 70 +22/-20 ka for the offset landforms. The minimum age of the alluvial fan deposits based on 36Cl depth profiles is 63 ?? 8 ka. Combining the offset measurement with the cosmogenic 10Be date yields a geologic fault slip rate of 4.2 +1.9/-1.1 mm yr-1, whereas the 36Cl data indicate 4.7 +0.9/-0.6 mm yr-1 of slip. Summing these slip rates with known rates on the Owens Valley, Hunter Mountain, and Stateline faults at similar latitudes suggests a total geologic slip rate across the northern ECSZ of ???8.5 to 10 mm yr-1. This rate is commensurate with the overall geodetic rate and implies that the apparent discrepancy between geologic and geodetic data observed in the Mojave section of the ECSZ does not extend north of the Garlock fault. Although the overall geodetic rates are similar, the best estimates based on geology predict higher strain rates in the eastern part of the ECSZ than to the west, whereas the observed geodetic strain is relatively constant. Copyright 2007 by the American Geophysical Union.

Cosmogenic 10Be and 36Cl geochronology of offset alluvial fans along the northern Death Valley fault zone: Implications for transient strain in the eastern California shear zone

NASA Astrophysics Data System (ADS)

Frankel, Kurt L.; Brantley, Katherine S.; Dolan, James F.; Finkel, Robert C.; Klinger, Ralph E.; Knott, Jeffrey R.; Machette, Michael N.; Owen, Lewis A.; Phillips, Fred M.; Slate, Janet L.; Wernicke, Brian P.

2007-06-01

The northern Death Valley fault zone (NDVFZ) has long been recognized as a major right-lateral strike-slip fault in the eastern California shear zone (ECSZ). However, its geologic slip rate has been difficult to determine. Using high-resolution digital topographic imagery and terrestrial cosmogenic nuclide dating, we present the first geochronologically determined slip rate for the NDVFZ. Our study focuses on the Red Wall Canyon alluvial fan, which exposes clean dextral offsets of seven channels. Analysis of airborne laser swath mapping data indicates ˜297 ± 9 m of right-lateral displacement on the fault system since the late Pleistocene. In situ terrestrial cosmogenic 10Be and 36Cl geochronology was used to date the Red Wall Canyon fan and a second, correlative fan also cut by the fault. Beryllium 10 dates from large cobbles and boulders provide a maximum age of 70 +22/-20 ka for the offset landforms. The minimum age of the alluvial fan deposits based on 36Cl depth profiles is 63 ± 8 ka. Combining the offset measurement with the cosmogenic 10Be date yields a geologic fault slip rate of 4.2 +1.9/-1.1 mm yr-1, whereas the 36Cl data indicate 4.7 +0.9/-0.6 mm yr-1 of slip. Summing these slip rates with known rates on the Owens Valley, Hunter Mountain, and Stateline faults at similar latitudes suggests a total geologic slip rate across the northern ECSZ of ˜8.5 to 10 mm yr-1. This rate is commensurate with the overall geodetic rate and implies that the apparent discrepancy between geologic and geodetic data observed in the Mojave section of the ECSZ does not extend north of the Garlock fault. Although the overall geodetic rates are similar, the best estimates based on geology predict higher strain rates in the eastern part of the ECSZ than to the west, whereas the observed geodetic strain is relatively constant.

Geodetic Measurement of Deformation East of the San Andreas Fault in Central California

NASA Technical Reports Server (NTRS)

Sauber, Jeanne M.; Lisowski, Michael; Solomon, Sean C.

1988-01-01

Triangulation and trilateration data from two geodetic networks located between the western edge of the Great Valley and the San Andreas fault have been used to calculate shear strain rates in the Diablo Range and to estimate the slip rate along the Calaveras and Paicines faults in Central California. Within the Diablo Range the average shear strain rate was determined for the time period between 1962 and 1982 to be 0.15 + or - 0.08 microrad/yr, with the orientation of the most compressive strain at N 16 deg E + or - 14 deg. The orientation of the principal compressive strain predicted from the azimuth of the major structures in the region is N 25 deg E. It is inferred that the measured strain is due to compression across the folds of this area: the average shear straining corresponds to a relative shortening rate of 4.5 + or - 2.4 mm/yr. From an examination of wellbore breakout orientations and the azimuths of P-axes from earthquake focal mechanisms the inferred orientation of maximum compressive stress was found to be similar to the direction of maximum compressive strain implied by the trend of local fold structures. Results do not support the hypothesis of uniform fault-normal compression within the Coast Ranges. From trilateration measurements made between 1972 and 1987 on lines that are within 10 km of the San Andreas fault, a slip rate of 10 to 12 mm/yr was calculated for the Calaveras-Paicines fault south of Hollister. The slip rate of the Paicines fault decreases to 4 mm/yr near Bitter.

Repetition of large stress drop earthquakes on Wairarapa fault, New Zealand, revealed by LiDAR data

NASA Astrophysics Data System (ADS)

Delor, E.; Manighetti, I.; Garambois, S.; Beaupretre, S.; Vitard, C.

2013-12-01

We have acquired high-resolution LiDAR topographic data over most of the onland trace of the 120 km-long Wairarapa strike-slip fault, New Zealand. The Wairarapa fault broke in a large earthquake in 1855, and this historical earthquake is suggested to have produced up to 18 m of lateral slip at the ground surface. This would make this earthquake a remarkable event having produced a stress drop much higher than commonly observed on other earthquakes worldwide. The LiDAR data allowed us examining the ground surface morphology along the fault at < 50 cm resolution, including in the many places covered with vegetation. In doing so, we identified more than 900 alluvial features of various natures and sizes that are clearly laterally offset by the fault. We measured the about 670 clearest lateral offsets, along with their uncertainties. Most offsets are lower than 100 m. Each measurement was weighted by a quality factor that quantifies the confidence level in the correlation of the paired markers. Since the slips are expected to vary along the fault, we analyzed the measurements in short, 3-5 km-long fault segments. The PDF statistical analysis of the cumulative offsets per segment reveals that the alluvial morphology has well recorded, at every step along the fault, no more than a few (3-6), well distinct cumulative slips, all lower than 80 m. Plotted along the entire fault, the statistically defined cumulative slip values document four, fairly continuous slip profiles that we attribute to the four most recent large earthquakes on the Wairarapa fault. The four slip profiles have a roughly triangular and asymmetric envelope shape that is similar to the coseismic slip distributions described for most large earthquakes worldwide. The four slip profiles have their maximum slip at the same place, in the northeastern third of the fault trace. The maximum slips vary from one event to another in the range 7-15 m; the most recent 1855 earthquake produced a maximum coseismic slip of 15 × 2 m at the ground surface. Our results thus confirm that the Wairarapa fault breaks in remarkably large stress drop earthquakes. Those repeating large earthquakes share both similar (rupture length, slip-length distribution, location of maximum slip) and distinct (maximum slip amplitudes) characteristics. Furthermore, the seismic behavior of the Wairarapa fault is markedly different from that of nearby large strike-slip faults (Wellington, Hope). The reasons for those differences in rupture behavior might reside in the intrinsic properties of the broken faults, especially in their structural maturity.

A three-step Maximum-A-Posterior probability method for InSAR data inversion of coseismic rupture with application to four recent large earthquakes in Asia

NASA Astrophysics Data System (ADS)

Sun, J.; Shen, Z.; Burgmann, R.; Liang, F.

2012-12-01

We develop a three-step Maximum-A-Posterior probability (MAP) method for coseismic rupture inversion, which aims at maximizing the a posterior probability density function (PDF) of elastic solutions of earthquake rupture. The method originates from the Fully Bayesian Inversion (FBI) and the Mixed linear-nonlinear Bayesian inversion (MBI) methods , shares the same a posterior PDF with them and keeps most of their merits, while overcoming its convergence difficulty when large numbers of low quality data are used and improving the convergence rate greatly using optimization procedures. A highly efficient global optimization algorithm, Adaptive Simulated Annealing (ASA), is used to search for the maximum posterior probability in the first step. The non-slip parameters are determined by the global optimization method, and the slip parameters are inverted for using the least squares method without positivity constraint initially, and then damped to physically reasonable range. This step MAP inversion brings the inversion close to 'true' solution quickly and jumps over local maximum regions in high-dimensional parameter space. The second step inversion approaches the 'true' solution further with positivity constraints subsequently applied on slip parameters using the Monte Carlo Inversion (MCI) technique, with all parameters obtained from step one as the initial solution. Then the slip artifacts are eliminated from slip models in the third step MAP inversion with fault geometry parameters fixed. We first used a designed model with 45 degree dipping angle and oblique slip, and corresponding synthetic InSAR data sets to validate the efficiency and accuracy of method. We then applied the method on four recent large earthquakes in Asia, namely the 2010 Yushu, China earthquake, the 2011 Burma earthquake, the 2011 New Zealand earthquake and the 2008 Qinghai, China earthquake, and compared our results with those results from other groups. Our results show the effectiveness of the method in earthquake studies and a number of advantages of it over other methods. The details will be reported on the meeting.

Seismic velocity change and slip rate during the 2006 Guerrero (Mexico) slow slip event

NASA Astrophysics Data System (ADS)

Rivet, Diane; Radiguet, Mathilde; Campillo, Michel; Cotton, Fabrice; Shapiro, Nikolai; Krishna Singh, Shri; Kostoglodov, Vladimir

2010-05-01

We measure temporal change of the seismic velocity in the crust below the Guerrero region during the 2006 slow sleep event (SSE). We use repeated cross-correlations of ambient seismic noise recorded at 26 broad-band stations of the MesoAmerica Seismic Experiment (MASE). The cross-correlations are computed over 90 days with a moving window of 10 days from January 2005 to July 2007. To insure measurements independent of noise source variations, we only take into account the travel time change within the coda. For period of 8 to 20s, we observe a decrease in velocity starting in April 2006 with a maximum change of -0.3% of the initial velocity in June 2006. At these periods, the Rayleigh waves are sensitive to velocity changes down to the lower crust. In the other hand, we compute the deformation rate below the MASE array from a slip propagation model of the SSE observed by means of the displacement time-series of 15 continuous GPS stations. Slip initiates in the western part of the Guerrero Gap and propagates southeastward. The propagation velocity is of the order of 1 km/day. We then compare the seismic velocity change measured from continuous seismological data with the deformation rate inferred from geodetic measurements below the MASE array. We obtain a good agreement between the time of maximal seismic velocity change (July 2006) and the time of maximum deformation associated with the SSE (July to August 2006). This result shows that the long-term velocity change associated with the SSE can be detected using continuous seismic recordings. Since the SSE does not emit seismic waves, which interact with the superficial layers, the result indicates that the velocity change is due to deformation at depth.

Thrust Slip Rates as a Control on the Presence and Spatial Distribution of High Metamorphic Heating Rates in Collisional Systems: The "Hot Iron" Model Revisited

NASA Astrophysics Data System (ADS)

Thigpen, R.; Ashley, K. T.; Law, R. D.; Mako, C. A.

2017-12-01

In natural systems, two key observations indicate that major strain discontinuities such as faults and shear zones should play a fundamental role in orogenic thermal evolution: (1) Large faults and shear zones often separate components of the composite orogen that have experienced broadly different thermal and deformational histories, and (2) quantitative metamorphic and diffusional studies indicate that heating rates are much faster and the duration of peak conditions much shorter in natural collisional systems than those predicted by numerical continuum deformation models. Because heat transfer processes such as conduction usually operate at much slower time scales than rates of other tectonic processes, thermal evolution is often transient and thus can be strongly influenced by tectonic disturbances that occur at rates much faster than thermal relaxation. Here, we use coupled thermal-mechanical finite element models of thrust faults to explore how fault slip rate may fundamentally influence the thermal evolution of individual footwall and hanging wall thrust slices. The model geometry involves a single crustal-scale thrust with a dip of 25° that is translated up the ramp at average velocities of 20, 35, and 50 km Myr-1, interpreted to represent average to relatively high slip rates observed in many collisional systems. Boundary conditions include crustal radioactive heat production, basal mantle heat flow, and surface erosion rates that are a function of thrust rate and subsequent topography generation. In the models, translation of the hanging wall along the crustal-scale detachment results in erosion, exhumation, and retrograde metamorphism of the emerging hanging wall topography and coeval burial, `hot iron' heating, and prograde metamorphism of the thrust footwall. Thrust slip rates of 20, 35, and 50 km Myr-1 yield maximum footwall heating rates ranging from 55-90° C Myr-1 and maximum hanging wall cooling rates of 138-303° C Myr-1. These relatively rapid heating rates explain, in part, the presence of chemical diffusion profiles in metamorphic minerals that are indicative of high heating rates. Additionally, the relatively high cooling rates explain preservation of chemical zoning, as rapid cooling prevents diffusive profiles from being substantially modified during exhumation.

Slip rate and earthquake recurrence along the central Septentrional fault, North American-Caribbean plate boundary, Dominican Republic

USGS Publications Warehouse

Prentice, C.S.; Mann, P.; Pena, L.R.; Burr, G.

2003-01-01

The Septentrional fault zone (SFZ) is the major North American-Caribbean, strike-slip, plate boundary fault at the longitude of eastern Hispaniola. The SFZ traverses the densely populated Cibao Valley of the Dominican Republic, forming a prominent scarp in alluvium. Our studies at four sites along the central SFZ are aimed at quantifying the late Quaternary behavior of this structure to better understand the seismic hazard it represents for the northeastern Caribbean. Our investigations of excavations at sites near Rio Cenovi show that the most recent ground-rupturing earthquake along this fault in the north central Dominican Republic occurred between A.D. 1040 and A.D. 1230, and involved a minimum of ???4 m of left-lateral slip and 2.3 m of normal dip slip at that site. Our studies of offset stream terraces at two locations, Rio Juan Lopez and Rio Licey, provide late Holocene slip rate estimates of 6-9 mm/yr and a maximum of 11-12 mm/yr, respectively, across the Septentrional fault. Combining these results gives a best estimate of 6-12 mm/yr for the slip rate across the SFZ. Three excavations, two near Tenares and one at the Rio Licey site, yielded evidence for the occurrence of earlier prehistoric earthquakes. Dates of strata associated with the penultimate event suggest that it occurred post-A.D. 30, giving a recurrence interval of 800-1200 years. These studies indicate that the SFZ has likely accumulated elastic strain sufficient to generate a major earthquake during the more than 800 years since it last slipped and should be considered likely to produce a destructive future earthquake.

Late Quaternary Slip Rate Along the Selaha Fault, Central Segment of the Xianshuihe Fault System, Eastern Tibet, and Regional Paleoclimate Reconstruction

NASA Astrophysics Data System (ADS)

Chevalier, M. L.; Bai, M.; Pan, J.; Replumaz, A.; Leloup, P. H.; Li, H.

2017-12-01

The left-slip Xianshuihe fault system in E Tibet is considered as one of the most tectonically active fault system in China. Studying its activity, especially its slip rate at different time scales, is essential to evaluate regional earthquake hazards. Here, we focus on the central segment, where the Xianshuihe fault splays into three branches: the Selaha, Yalahe and Zheduotang faults. We use 10Be cosmogenic dating at 3 sites where the active Selaha fault cuts and left-laterally offsets moraine crests and levees. By matching their emplacement ages with their offsets, we obtain a conservative late Quaternary horizontal slip-rate of 5.7-12 mm/yr at TG levees and SLH moraine, or 9.6-9.9 mm/yr assuming that the slip rate should be constant between the two nearby sites. At YJG moraine, we obtain a lower slip rate of 4.4±0.5 mm/yr, most likely because the parallel Zheduotang fault shares the slip rate at this longitude, therefore suggesting a 5 mm/yr slip rate along the Zheduotang fault. A higher slip rate along the short ( 60 km) and discontinuous Selaha fault compared to that along the long ( 300 km) and linear Ganzi fault (7 mm/yr) suggests a high earthquake hazard in the densely populated city of Kangding. Using the moraine ages that we determined here in addition to our previous studies in the same region allows us to study the timing and extent of past glaciations in the Himalayan-Tibetan orogen. This is essential to reconstruct regional paleoclimate and to understand variations in the atmospheric circulation due to the high-altitude low latitude Tibetan Plateau, in order to possibly predict future climate changes. We dated 6 glacial deposits from SE Tibet using 10Be cosmogenic dating on 68 boulders and only found advances during the Last Glacial Maximum (limited) and Marine Isotope Stage-6 (extensive), with no signal in between. That the two coldest periods are LGM and MIS-6 is in agreement with the Northern hemisphere cooling cycles, suggesting that in SE Tibet, glaciers are more sensitive to a decrease of temperature rather than an increase of precipitation and that they respond to the Northern hemisphere cooling cycles rather than to the South Asian summer monsoon. This explains the absence of MIS-3 advances, in contradiction with what is observed in W Tibet where they are the most extensive.

Quaternary low-angle slip on detachment faults in Death Valley, California

USGS Publications Warehouse

Hayman, N.W.; Knott, J.R.; Cowan, D.S.; Nemser, E.; Sarna-Wojcicki, A. M.

2003-01-01

Detachment faults on the west flank of the Black Mountains (Nevada and California) dip 29??-36?? and cut subhorizontal layers of the 0.77 Ma Bishop ash. Steeply dipping normal faults confined to the hanging walls of the detachments offset layers of the 0.64 Ma Lava Creek B tephra and the base of 0.12-0.18 Ma Lake Manly gravel. These faults sole into and do not cut the low-angle detachments. Therefore the detachments accrued any measurable slip across the kinematically linked hanging-wall faults. An analysis of the orientations of hundreds of the hanging-wall faults shows that extension occurred at modest slip rates (<1 mm/yr) under a steep to vertically oriented maximum principal stress. The Black Mountain detachments are appropriately described as the basal detachments of near-critical Coulomb wedges. We infer that the formation of late Pleistocene and Holocene range-front fault scarps accompanied seismogenic slip on the detachments.

Uncertainties in slip-rate estimates for the Mission Creek strand of the southern San Andreas fault at Biskra Palms Oasis, southern California

USGS Publications Warehouse

Behr, W.M.; Rood, D.H.; Fletcher, K.E.; Guzman, N.; Finkel, R.; Hanks, T.C.; Hudnut, K.W.; Kendrick, K.J.; Platt, J.P.; Sharp, W.D.; Weldon, R.J.; Yule, J.D.

2010-01-01

This study focuses on uncertainties in estimates of the geologic slip rate along the Mission Creek strand of the southern San Andreas fault where it offsets an alluvial fan (T2) at Biskra Palms Oasis in southern California. We provide new estimates of the amount of fault offset of the T2 fan based on trench excavations and new cosmogenic 10Be age determinations from the tops of 12 boulders on the fan surface. We present three alternative fan offset models: a minimum, a maximum, and a preferred offset of 660 m, 980 m, and 770 m, respectively. We assign an age of between 45 and 54 ka to the T2 fan from the 10Be data, which is significantly older than previously reported but is consistent with both the degree of soil development associated with this surface, and with ages from U-series geochronology on pedogenic carbonate from T2, described in a companion paper by Fletcher et al. (this volume). These new constraints suggest a range of slip rates between ~12 and 22 mm/yr with a preferred estimate of ~14-17 mm/yr for the Mission Creek strand of the southern San Andreas fault. Previous studies suggested that the geologic and geodetic slip-rate estimates at Biskra Palms differed. We find, however, that considerable uncertainty affects both the geologic and geodetic slip-rate estimates, such that if a real discrepancy between these rates exists for the southern San Andreas fault at Biskra Palms, it cannot be demonstrated with available data. ?? 2010 Geological Society of America.

What Is Better Than Coulomb Failure Stress? A Ranking of Scalar Static Stress Triggering Mechanisms from 105 Mainshock-Aftershock Pairs

NASA Astrophysics Data System (ADS)

Meade, Brendan J.; DeVries, Phoebe M. R.; Faller, Jeremy; Viegas, Fernanda; Wattenberg, Martin

2017-11-01

Aftershocks may be triggered by the stresses generated by preceding mainshocks. The temporal frequency and maximum size of aftershocks are well described by the empirical Omori and Bath laws, but spatial patterns are more difficult to forecast. Coulomb failure stress is perhaps the most common criterion invoked to explain spatial distributions of aftershocks. Here we consider the spatial relationship between patterns of aftershocks and a comprehensive list of 38 static elastic scalar metrics of stress (including stress tensor invariants, maximum shear stress, and Coulomb failure stress) from 213 coseismic slip distributions worldwide. The rates of true-positive and false-positive classification of regions with and without aftershocks are assessed with receiver operating characteristic analysis. We infer that the stress metrics that are most consistent with observed aftershock locations are maximum shear stress and the magnitude of the second and third invariants of the stress tensor. These metrics are significantly better than random assignment at a significance level of 0.005 in over 80% of the slip distributions. In contrast, the widely used Coulomb failure stress criterion is distinguishable from random assignment in only 51-64% of the slip distributions. These results suggest that a number of alternative scalar metrics are better predictors of aftershock locations than classic Coulomb failure stress change.

Structure and lithology of the Japan Trench subduction plate boundary fault

NASA Astrophysics Data System (ADS)

Kirkpatrick, James D.; Rowe, Christie D.; Ujiie, Kohtaro; Moore, J. Casey; Regalla, Christine; Remitti, Francesca; Toy, Virginia; Wolfson-Schwehr, Monica; Kameda, Jun; Bose, Santanu; Chester, Frederick M.

2015-01-01

The 2011 Mw9.0 Tohoku-oki earthquake ruptured to the trench with maximum coseismic slip located on the shallow portion of the plate boundary fault. To investigate the conditions and physical processes that promoted slip to the trench, Integrated Ocean Drilling Program Expedition 343/343T sailed 1 year after the earthquake and drilled into the plate boundary ˜7 km landward of the trench, in the region of maximum slip. Core analyses show that the plate boundary décollement is localized onto an interval of smectite-rich, pelagic clay. Subsidiary structures are present in both the upper and lower plates, which define a fault zone ˜5-15m thick. Fault rocks recovered from within the clay-rich interval contain a pervasive scaly fabric defined by anastomosing, polished, and lineated surfaces with two predominant orientations. The scaly fabric is crosscut in several places by discrete contacts across which the scaly fabric is truncated and rotated, or different rocks are juxtaposed. These contacts are inferred to be faults. The plate boundary décollement therefore contains structures resulting from both distributed and localized deformation. We infer that the formation of both of these types of structures is controlled by the frictional properties of the clay: the distributed scaly fabric formed at low strain rates associated with velocity-strengthening frictional behavior, and the localized faults formed at high strain rates characterized by velocity-weakening behavior. The presence of multiple discrete faults resulting from seismic slip within the décollement suggests that rupture to the trench may be characteristic of this margin.

High-velocity frictional properties of chert in the Jurassic accretionary complex, central Japan

NASA Astrophysics Data System (ADS)

Motohashi, G.; Oohashi, K.; Ujiie, K.

2017-12-01

Chert is one of the main components in accretionary complexes. Previous friction experiments on quartz-rich rocks at slip rates of 0.1-100 mm/s revealed that fault weakening was caused by a thixotropic behavior of silica gel [Goldsby and Tullis, 2002; Di Toro et al., 2004; Hayashi and Tsutsumi, 2010]. We conducted high-velocity friction experiments on chert at a slip rate of 1.3 m/s and normal stresses of 5-13 MPa under room humidity conditions and examined the resultant microstructures. During experiments, temperatures were measured using a high-resolution infrared thermal-imaging camera, and the process of shearing was monitored by a digital video camera. The samples for experiments were collected from the host rock (gray chert) of the thrust fault in the Jurassic accretionary complex, central Japan. Experimental data indicated that slip strengthening occurred after first slip weakening. This was followed by second slip weakening toward a steady-state friction, with maximum temperature being less than 1200 °C. The melt patches developed during slip strengthening, while the growth of melt layer was recognized during and after second slip weakening. The melt patches included little chert fragments, and the color of the chert surrounding melt patches was changed to dark, possibly representing thermal alteration of quartz grains. After second slip weakening, the volume fraction of chert fragments in the melt layer increased, and the chert fragments and the wall rocks adjacent to the melt layer were intensely cracked. These features indicated that the growth of melt layer was accompanied by the incorporation of cracked wall rocks, suggesting that off-fault damage may be linked to the slip behavior during and after second slip weakening. Goldsby, D. L., T. E. Tullis (2002), Geophys. Res. Lett., 29(17), 1844. Di Toro, G., D. L. Goldsby, T. E. Tullis (2004), Nature, 427, 436-439. Hayashi, N., A. Tsutsumi (2010), Geophys. Res. Lett., 37, L12305.

Seismic Supercycles of Normal Faults in Central Italy over Various Time Scales Revealed by 36Cl Cosmogenic Dating

NASA Astrophysics Data System (ADS)

Benedetti, L. C.; Tesson, J.; Perouse, E.; Puliti, I.; Fleury, J.; Rizza, M.; Billant, J.; Pace, B.

2017-12-01

The use of 36Cl cosmogenic nuclide as a paleoseismological tool for normal faults in the Mediterranean has revolutionized our understanding of their seismic cycle (Gran Mitchell et al. 2001, Benedetti et al. 2002). Here we synthetized results obtained on 13 faults in Central Italy. Those records cover a period of 8 to 45 ka. The mean recurrence time of retrieved seismic events is 5.5 ±6 ka, with a mean slip per event of 2.5 ± 1.8 m and a mean slip-rate from 0.1 to 2.4 mm/yr. Most retrieved events correspond to single events according to scaling relationships. This is also supported by the 2 m-high co-seismic slip observed on the Mt Vettore fault after the October 30, 2016 M6.5 earthquake in Central Italy (EMERGEO working group). Our results suggest that all faults have experienced one or several periods of slip acceleration with bursts of seismic activity, associated with very high slip-rate of 1.7-9 mm/yr, corresponding to 2-20 times their long-term slip-rate. The duration of those bursts is variable from a fault to another (from < 2 kyr to 4-10 kyr). Those periods of acceleration are generally separated by longer periods of quiescence with no or very few events. Those alternating periods correspond to a long-term variation of the strain level with all faults oscillating between strain maximum and minimum, the length of strain loading and release being significantly different from one fault to another, those supercycles occurring over periods of 8 to 45 ka. We found relationships between the mean slip-rate, the mean slip per event and the mean recurrence time. This might suggest that the seismic activity of those faults could be controlled by their intrinsic properties (e.g. long-term slip-rate, fault-length, state of structural maturity). Our results also show events clustering with several faults rupturing in less than 500 yrs on adjacent or distant faults within the studied area. The Norcia-Amatrice seismic sequence, ≈ 50 km north of our study area, also evidenced this clustering behaviour, with over the last 20 yrs several successive events of Mw 5 to 6.5 (from north to south: Colfiorito 1997 Mw6.0, Norcia 2016 Mw6.5, L'Aquila 2009 Mw6.3), rupturing various fault systems, over a total length of ≈100 km. This sequence will allow to better understand earthquake kinematics and spatiotemporal slip distribution during those seismic bursts.

An acoustic emission study of plastic deformation in polycrystalline aluminium

NASA Technical Reports Server (NTRS)

Bill, R. C.; Frederick, J. R.; Felbeck, D. K.

1979-01-01

Acoustic emission experiments were performed on polycrystalline and single crystal 99.99% aluminum while undergoing tensile deformation. It was found that acoustic emission counts as a function of grain size showed a maximum value at a particular grain size. Furthermore, the slip area associated with this particular grain size corresponded to the threshold level of detectability of single dislocation slip events. The rate of decline in acoustic emission activity as grain size is increased beyond the peak value suggests that grain boundary associated dislocation sources are giving rise to the bulk of the detected acoustic emissions.

Streaming potential of superhydrophobic microchannels.

PubMed

Park, Hung Mok; Kim, Damoa; Kim, Se Young

2017-03-01

For the purpose of gaining larger streaming potential, it has been suggested to employ superhydrophobic microchannels with a large velocity slip. There are two kinds of superhydrophobic surfaces, one having a smooth wall with a large Navier slip coefficient caused by the hydrophobicity of the wall material, and the other having a periodic array of no- shear slots of air pockets embedded in a nonslip wall. The electrokinetic flows over these two superhydrophobic surfaces are modelled using the Navier-Stokes equation and convection-diffusion equations of the ionic species. The Navier slip coefficient of the first kind surfaces and the no-shear slot ratio of the second kind surfaces are similar in the sense that the volumetric flow rate increases as these parameter values increase. However, although the streaming potential increases monotonically with respect to the Navier slip coefficient, it reaches a maximum and afterward decreases as the no-shear ratio increases. The results of the present investigation imply that the characterization of superhydrophobic surfaces employing only the measurement of volumetric flow rate against pressure drop is not appropriate and the fine structure of the superhydrophobic surfaces must be verified before predicting the streaming potential and electrokinetic flows accurately. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Can Recovery Foot Placement Affect Older Adults' Slip-Fall Severity?

PubMed

Wang, Shuaijie; Liu, Xuan; Lee, Anna; Pai, Yi-Chung

2017-08-01

Following a slip occurred in the overground walking, a fall can be classified into two exclusive categories: feet-forward fall or split fall. The purposes of this study were to investigate whether the placement of the recovery foot would determine the slip types, the likelihood of fall, and the severity associated with each fall. The fall severity was estimated based on the impact velocity of body segments or trunk orientation upon fall arrest. One hundred ninety-five participants experienced a novel, unannounced slip while walking on a 7-m walkway. Kinematics of a full-body marker set was collected by a motion capture system which was synchronized with the force plates and loadcell. The results showed that the recovery foot landing position relative to the projected center of mass position at the recovery foot touchdown determined the slip type by 90.8%. Feet-forward slips led to significantly lower rate of falls than did split slips (47.6 vs. 67.8%, p < 0.01). Yet, feet-forward falls were much more dangerous because they were associated with significantly greater estimated maximum hip impact velocity (p < 0.001) and trunk backward leaning angle (p < 0.001) in comparison to split falls.

Turbulent flows over superhydrophobic surfaces with shear-dependent slip length

NASA Astrophysics Data System (ADS)

Khosh Aghdam, Sohrab; Seddighi, Mehdi; Ricco, Pierre

2015-11-01

Motivated by recent experimental evidence, shear-dependent slip length superhydrophobic surfaces are studied. Lyapunov stability analysis is applied in a 3D turbulent channel flow and extended to the shear-dependent slip-length case. The feedback law extracted is recognized for the first time to coincide with the constant-slip-length model widely used in simulations of hydrophobic surfaces. The condition for the slip parameters is found to be consistent with the experimental data and with values from DNS. The theoretical approach by Fukagata (PoF 18.5: 051703) is employed to model the drag-reduction effect engendered by the shear-dependent slip-length surfaces. The estimated drag-reduction values are in very good agreement with our DNS data. For slip parameters and flow conditions which are potentially realizable in the lab, the maximum computed drag reduction reaches 50%. The power spent by the turbulent flow on the walls is computed, thereby recognizing the hydrophobic surfaces as a passive-absorbing drag-reduction method, as opposed to geometrically-modifying techniques that do not consume energy, e.g. riblets, hence named passive-neutral. The flow is investigated by visualizations, statistical analysis of vorticity and strain rates, and quadrants of the Reynolds stresses. Part of this work was funded by Airbus Group. Simulations were performed on the ARCHER Supercomputer (UKTC Grant).

Slip resistance of winter footwear on snow and ice measured using maximum achievable incline.

PubMed

Hsu, Jennifer; Shaw, Robert; Novak, Alison; Li, Yue; Ormerod, Marcus; Newton, Rita; Dutta, Tilak; Fernie, Geoff

2016-05-01

Protective footwear is necessary for preventing injurious slips and falls in winter conditions. Valid methods for assessing footwear slip resistance on winter surfaces are needed in order to evaluate footwear and outsole designs. The purpose of this study was to utilise a method of testing winter footwear that was ecologically valid in terms of involving actual human testers walking on realistic winter surfaces to produce objective measures of slip resistance. During the experiment, eight participants tested six styles of footwear on wet ice, on dry ice, and on dry ice after walking over soft snow. Slip resistance was measured by determining the maximum incline angles participants were able to walk up and down in each footwear-surface combination. The results indicated that testing on a variety of surfaces is necessary for establishing winter footwear performance and that standard mechanical bench tests for footwear slip resistance do not adequately reflect actual performance. Practitioner Summary: Existing standardised methods for measuring footwear slip resistance lack validation on winter surfaces. By determining the maximum inclines participants could walk up and down slopes of wet ice, dry ice, and ice with snow, in a range of footwear, an ecologically valid test for measuring winter footwear performance was established.

Slip resistance of winter footwear on snow and ice measured using maximum achievable incline

PubMed Central

Hsu, Jennifer; Shaw, Robert; Novak, Alison; Li, Yue; Ormerod, Marcus; Newton, Rita; Dutta, Tilak; Fernie, Geoff

2016-01-01

Abstract Protective footwear is necessary for preventing injurious slips and falls in winter conditions. Valid methods for assessing footwear slip resistance on winter surfaces are needed in order to evaluate footwear and outsole designs. The purpose of this study was to utilise a method of testing winter footwear that was ecologically valid in terms of involving actual human testers walking on realistic winter surfaces to produce objective measures of slip resistance. During the experiment, eight participants tested six styles of footwear on wet ice, on dry ice, and on dry ice after walking over soft snow. Slip resistance was measured by determining the maximum incline angles participants were able to walk up and down in each footwear–surface combination. The results indicated that testing on a variety of surfaces is necessary for establishing winter footwear performance and that standard mechanical bench tests for footwear slip resistance do not adequately reflect actual performance. Practitioner Summary: Existing standardised methods for measuring footwear slip resistance lack validation on winter surfaces. By determining the maximum inclines participants could walk up and down slopes of wet ice, dry ice, and ice with snow, in a range of footwear, an ecologically valid test for measuring winter footwear performance was established. PMID:26555738

Crustal strain near the Big Bend of the San Andreas Fault: analysis of the Los Padres-Tehachapi Trilateration Networks, California

USGS Publications Warehouse

Eberhart-Phillips, D.; Lisowski, M.

1990-01-01

In the region of the Los Padres-Tehachapi geodetic network, the San Andreas fault (SAF) changes its orientation by over 30?? from N40??W, close to that predicted by plate motion for a transform boundary, to N73??W. The strain orientation near the SAF is consistent with right-lateral shear along the fault, with maximum shear rate of 0.38??0.01??rad/yr at N63??W. In contrast, away from the SAF the strain orientations on both sides of the fault are consistent with the plate motion direction, with maximum shear rate of 0.19??0.01??rad/yr at N44??W. The best fitting Garlock fault model had computed left-lateral slip rate of 11??2mm/yr below 10km. Buried left-lateral slip of 15??6mm/yr on the Big Pine fault, within the Western Transverse Ranges, provides significant reduction in line length residuals; however, deformation there may be more complicated than a single vertical fault. A subhorizontal detachment on the southern side of the SAF cannot be well constrained by these data. -from Authors

Retention of the "first-trial effect" in gait-slip among community-living older adults.

PubMed

Liu, Xuan; Bhatt, Tanvi; Wang, Shuaijie; Yang, Feng; Pai, Yi-Chung Clive

2017-02-01

"First-trial effect" characterizes the rapid adaptive behavior that changes the performance outcome (from fall to non-fall) after merely a single exposure to postural disturbance. The purpose of this study was to investigate how long the first-trial effect could last. Seventy-five (≥ 65 years) community-dwelling older adults, who were protected by an overhead full body harness system, were retested for a single slip 6-12 months after their initial exposure to a single gait-slip. Subjects' body kinematics that was used to compute their proactive (feedforward) and reactive (feedback) control of stability was recorded by an eight-camera motion analysis system. We found the laboratory falls of subjects on their retest slip were significantly lower than that on the novel initial slip, and the reactive stability of these subjects was also significantly improved. However, the proactive stability of subjects remains unchanged between their initial slip and retest slip. The fall rates and stability control had no difference among the 6-, 9-, and 12-month retest groups, which indicated a maximum retention on 12 months after a single slip in the laboratory. These results highlighted the importance of the "first-trial effect" and suggested that perturbation training is effective for fall prevention, with lower trial doses for a long period (up to 1 year). Therefore, single slip training might benefit those older adults who could not tolerate larger doses in reality.

New Holocene Slip-rate Sites Along the Mojave San Andreas Fault Near Palmdale, CA

NASA Astrophysics Data System (ADS)

Young, E. K.; Cowgill, E.; Scharer, K. M.

2016-12-01

The slip rate for the Mojave San Andreas fault (MSAF) is poorly known: the long-term ( 413ky) geologic rate is as high as 37mm/yr [1] while the geodetic slip rate is as low as 15mm/yr [2]. To determine the Holocene-average rate for the MSAF, we investigated several offset landforms near Palmdale, CA using detailed surficial mapping and 14C analyses of charcoal collected from hand-dug excavations. Site X-12 preserves two offset markers sourced from a north-flowing catchment south of the fault. One is a terrace riser cut into older alluvium that is abutted by the eastern margin of a Qf3 fan and is displaced by 75 m. Offset of the riser and the alluvium generated a north-facing fault-scarp that was eroded to form a small fan on top of the eastern margin of the Qf3 fan. The second offset is a beheaded channel that is incised into the Qf3 fan north of the fault and is displaced 50m, and thus formed after the riser was offset by 25m. To date these landforms we opened 5 excavations at the site, with emphasis on the beheaded channel. Dates from within the Qf3 fan south/upstream of the fault and abandoned bedload in the beheaded channel give maximum and minimum ages for the channel incision of 1500calBP and 600calBP, respectively, implying a rate ≥33mm/yr. Future work seeks to date post-abandonment channel-fill deposits and the upper and lower bounds on the terrace riser. At a second site, Ranch Center, a north-flowing stream cut across a shutter ridge north of the fault and was then offset and deflected 80m before cutting a new channel across the fault. Future work here seeks to date the bases of the alluvial fans deposited by the abandoned and active channels to obtain maximum and minimum ages for the 80 m offset, respectively. Rates from these sites should help to better define the Holocene slip rate on the MSAF. 1) Matmon et al., 2005, GSAB. v. 117 p. 795 2) Becker et al., 2005, Geoph.. J. Int., v. 160 p. 634

Gaseous slip flow analysis of a micromachined flow sensor for ultra small flow applications

NASA Astrophysics Data System (ADS)

Jang, Jaesung; Wereley, Steven T.

2007-02-01

The velocity slip of a fluid at a wall is one of the most typical phenomena in microscale gas flows. This paper presents a flow analysis considering the velocity slip in a capacitive micro gas flow sensor based on pressure difference measurements along a microchannel. The tangential momentum accommodation coefficient (TMAC) measurements of a particular channel wall in planar microchannels will be presented while the previous micro gas flow studies have been based on the same TMACs on both walls. The sensors consist of a pair of capacitive pressure sensors, inlet/outlet and a microchannel. The main microchannel is 128.0 µm wide, 4.64 µm deep and 5680 µm long, and operated under nearly atmospheric conditions where the outlet Knudsen number is 0.0137. The sensor was fabricated using silicon wet etching, ultrasonic drilling, deep reactive ion etching (DRIE) and anodic bonding. The capacitance change of the sensor and the mass flow rate of nitrogen were measured as the inlet-to-outlet pressure ratio was varied from 1.00 to 1.24. The measured maximum mass flow rate was 3.86 × 10-10 kg s-1 (0.019 sccm) at the highest pressure ratio tested. As the pressure difference increased, both the capacitance of the differential pressure sensor and the flow rate through the main microchannel increased. The laminar friction constant f sdot Re, an important consideration in sensor design, varied from the incompressible no-slip case and the mass sensitivity and resolution of this sensor were discussed. Using the current slip flow formulae, a microchannel with much smaller mass flow rates can be designed at the same pressure ratios.

Late Quaternary eruption of the Ranau Caldera and new geological slip rates of the Sumatran Fault Zone in Southern Sumatra, Indonesia

NASA Astrophysics Data System (ADS)

Natawidjaja, Danny Hilman; Bradley, Kyle; Daryono, Mudrik R.; Aribowo, Sonny; Herrin, Jason

2017-12-01

Over the last decade, studies of natural hazards in Sumatra have focused primarily on great earthquakes and associated tsunamis produced by rupture of the Sunda megathrust. However, the Sumatran Fault and the active volcanic arc present proximal hazards to populations on mainland Sumatra. At present, there is little reliable information on the maximum magnitudes and recurrence intervals of Sumatran Fault earthquakes, or the frequency of paroxysmal caldera-forming (VEI 7-8) eruptions. Here, we present new radiocarbon dates of paleosols buried under the voluminous Ranau Tuff that constrain the large caldera-forming eruption to around 33,830-33,450 calender year BP (95% probability). We use the lateral displacement of river channels incised into the Ranau Tuff to constrain the long-term slip rate of two segments of the Sumatran Fault. South of Ranau Lake, the Kumering segment preserves isochronous right-lateral channel offsets of approximately 350 ± 50 m, yielding a minimum slip rate of 10.4 ± 1.5 mm/year for the primary active fault trace. South of Suoh pull-apart depression, the West Semangko segment offsets the Semangko River by 230 ± 60 m, yielding an inferred slip rate of 6.8 ± 1.8 mm/year. Compared with previous studies, these results indicate more recent high-volume volcanism in South Sumatra and increased seismic potency of the southernmost segments of the Sumatran Fault Zone.

Microstructure, Texture, and Mechanical Behavior of As-cast Ni-Fe-W Matrix Alloy

NASA Astrophysics Data System (ADS)

Rao, A. Sambasiva; Manda, Premkumar; Mohan, M. K.; Nandy, T. K.; Singh, A. K.

2018-04-01

This article describes the tensile properties, flow, and work-hardening behavior of an experimental alloy 53Ni-29Fe-18W in as-cast condition. The microstructure of the alloy 53Ni-29Fe-18W displays single phase (fcc) in as-cast condition along with typical dendritic features. The bulk texture of the as-cast alloy reveals the triclinic sample symmetry and characteristic nature of coarse-grained materials. The alloy exhibits maximum strength ( σ YS and σ UTS) values along the transverse direction. The elongation values are maximum and minimum along the transverse and longitudinal directions, respectively. Tensile fracture surfaces of both the longitudinal and transverse samples display complete ductile fracture features. Two types of slip lines, namely, planar and intersecting, are observed in deformed specimens and the density of slip lines increases with increasing the amount of deformation. The alloy displays moderate in-plane anisotropy ( A IP) and reasonably low anisotropic index ( δ) values, respectively. The instantaneous or work-hardening rate curves portray three typical stages (I through III) along both the longitudinal and transverse directions. The alloy exhibits dislocation-controlled strain hardening during tensile testing, and slip is the predominant deformation mechanism.

A fault slip model of the 2016 Meinong, Taiwan, earthquake from near-source strong motion and high-rate GPS waveforms

NASA Astrophysics Data System (ADS)

Rau, Ruey-Juin; Wen, Yi-Ying; Tseng, Po-Ching; Chen, Wei-Cheng; Cheu, Chi-Yu; Hsieh, Min-Che; Ching, Kuo-En

2017-04-01

The 6 February 2016 MW 6.5 Meinong earthquake (03:57:26.1 local time) occurred at about 30 km ESE of the Tainan city with a focal depth of 14.6 km. It is a mid-crust moderate-sized event, however, produced widespread strong shaking in the 30-km-away Tainan city and caused about 10 buildings collapsed and 117 death. Furthermore, the earthquake created a 20 x 10 km2 dome-shaped structure with a maximum uplift of 13 cm in between the epicenter and the Tainan city. We collected 81 50-Hz GPS and 130 strong motion data recorded within 60 km epicentral distances. High-rate GPS data are processed with GIPSY 6.4 and the calculated GPS displacement wavefield record section shows 40-60 cm Peak Ground Displacement (PGD) concentrated at 25-30 km WNW of the epicenter. The large PGDs correspond to 65-85 cm/sec PGV, which are significantly larger than the near-fault ground motion collected from moderate-sized earthquakes occurred worldwide. To investigate the source properties of the causative fault, considering the azimuthal coverage and data quality, we selected waveform data from 10 50-Hz GPS stations and 10 free-field 200-Hz strong motion stations to invert for the finite source parameters using the non-negative least squares approach. A bandpass filter of 0.05-0.5 Hz is applied to both high-rate GPS data and strong motion data, with sampling rate of 0.1 sec. The fault plane parameters (strike 281 degrees, dip 24 degrees) derived from Global Centroid Moment Tensor (CMT) are used in the finite fault inversion. The results of our joint GPS and strong motion data inversion indicates two major slip patches. The first large-slip patch occurred just below the hypocenter propagating westward at a 15-25 km depth range. The second high-slip patch appeared at 5-10 km depth slipping westward under the western side of the erected structure shown by InSAR image. These two large-slip patches appeared to devoid of aftershock seismicity, which concentrated mainly at the low-slip zones.

Geodetic Imaging of the Earthquake Cycle

NASA Astrophysics Data System (ADS)

Tong, Xiaopeng

In this dissertation I used Interferometric Synthetic Aperture Radar (InSAR) and Global Positioning System (GPS) to recover crustal deformation caused by earthquake cycle processes. The studied areas span three different types of tectonic boundaries: a continental thrust earthquake (M7.9 Wenchuan, China) at the eastern margin of the Tibet plateau, a mega-thrust earthquake (M8.8 Maule, Chile) at the Chile subduction zone, and the interseismic deformation of the San Andreas Fault System (SAFS). A new L-band radar onboard a Japanese satellite ALOS allows us to image high-resolution surface deformation in vegetated areas, which is not possible with older C-band radar systems. In particular, both the Wenchuan and Maule InSAR analyses involved L-band ScanSAR interferometry which had not been attempted before. I integrated a large InSAR dataset with dense GPS networks over the entire SAFS. The integration approach features combining the long-wavelength deformation from GPS with the short-wavelength deformation from InSAR through a physical model. The recovered fine-scale surface deformation leads us to better understand the underlying earthquake cycle processes. The geodetic slip inversion reveals that the fault slip of the Wenchuan earthquake is maximum near the surface and decreases with depth. The coseismic slip model of the Maule earthquake constrains the down-dip extent of the fault slip to be at 45 km depth, similar to the Moho depth. I inverted for the slip rate on 51 major faults of the SAFS using Green's functions for a 3-dimensional earthquake cycle model that includes kinematically prescribed slip events for the past earthquakes since the year 1000. A 60 km thick plate model with effective viscosity of 10 19 Pa · s is preferred based on the geodetic and geological observations. The slip rates recovered from the plate models are compared to the half-space model. The InSAR observation reveals that the creeping section of the SAFS is partially locked. This high-resolution deformation model will refine the moment accumulation rates and shear strain rates, which are not well resolved by previous models.

The architecture and frictional properties of faults in shale

NASA Astrophysics Data System (ADS)

De Paola, Nicola; Murray, Rosanne; Stillings, Mark; Imber, Jonathan; Holdsworth, Robert

2015-04-01

The geometry of brittle fault zones and associated fracture patterns in shale rocks, as well as their frictional properties at reservoir conditions, are still poorly understood. Nevertheless, these factors may control the very low recovery factors (25% for gas and 5% for oil) obtained during fracking operations. Extensional brittle fault zones (maximum displacement ≤ 3 m) cut exhumed oil mature black shales in the Cleveland Basin (UK). Fault cores up to 50 cm wide accommodated most of the displacement, and are defined by a stair-step geometry, controlled by the reactivation of en-echelon, pre-existing joints in the protolith. Cores typically show a poorly developed damage zone, up to 25 cm wide, and sharp contact with the protolith rocks. Their internal architecture is characterised by four distinct fault rock domains: foliated gouges; breccias; hydraulic breccias; and a slip zone up to 20 mm thick, composed of a fine-grained black gouge. Hydraulic breccias are located within dilational jogs with aperture of up to 20 cm, composed of angular clasts of reworked fault and protolith rock, dispersed within a sparry calcite cement. Velocity-step and slide-hold-slide experiments at sub-seismic slip rates (microns/s) were performed in a rotary shear apparatus under dry, water and brine-saturated conditions, for displacements of up to 46 cm. Both the protolith shale and the slip zone black gouge display shear localization, velocity strengthening behaviour and negative healing rates. Experiments at seismic slip rates (1.3 m/s), performed on the same materials under dry conditions, show that after initial friction values of 0.5-0.55, friction decreases to steady-state values of 0.1-0.15 within the first 10 mm of slip. Contrastingly, water/brine saturated gouge mixtures, exhibit almost instantaneous attainment of very low steady-state sliding friction (0.1). Our field observations show that brittle fracturing and cataclastic flow are the dominant deformation mechanisms in the fault core of shale faults, where slip localization may lead to the development of a thin slip zone made of very fine-grained gouges. The velocity-strengthening behaviour and negative healing rates observed during our laboratory experiments, suggest that slow, stable sliding faulting should take place within the protolith rocks and slip zone gouges. This behaviour will cause slow fault/fracture propagation, affecting the rate at which new fracture areas are created and, hence, limiting oil and gas production during reservoir stimulation. During slipping events, fluid circulation may be very effective along the fault zone at dilational jogs - where oil and gas production should be facilitated by the creation of large fracture areas - and rather restricted in the adjacent areas of the protolith, due to the lack of a well-developed damage zone and the low permeability of the matrix and slip zone gouge. Finally, our experiments performed at seismic slip rates show that seismic ruptures may still be able to propagate in a very efficient way within the slip zone of fluid-saturated shale faults, due to the attainment of instantaneous weakening.

Bond–Slip Relationship for CFRP Sheets Externally Bonded to Concrete under Cyclic Loading

PubMed Central

Li, Ke; Cao, Shuangyin; Yang, Yue; Zhu, Juntao

2018-01-01

The objective of this paper was to explore the bond–slip relationship between carbon fiber-reinforced polymer (CFRP) sheets and concrete under cyclic loading through experimental and analytical approaches. Modified beam tests were performed in order to gain insight into the bond–slip relationship under static and cyclic loading. The test variables are the CFRP-to-concrete width ratio, and the bond length of the CFRP sheets. An analysis of the test results in this paper and existing test results indicated that the slope of the ascending segment of the bond–slip curve decreased with an increase in the number of load cycles, but the slip corresponding to the maximum shear stress was almost invariable as the number of load cycles increased. In addition, the rate of reduction in the slope of the ascending range of the bond–slip curve during cyclic loading decreased as the concrete strength increased, and increased as the load level or CFRP-to-concrete width ratio enhanced. However, these were not affected by variations in bond length if the residual bond length was longer than the effective bond length. A bilinear bond–slip model for CFRP sheets that are externally bonded to concrete under cyclic loading, which considered the effects of the cyclic load level, concrete strength, and CFRP-to-concrete ratio, was developed based on the existing static bond–slip model. The accuracy of this proposed model was verified by a comparison between this proposed model and test results. PMID:29495383

Bond-Slip Relationship for CFRP Sheets Externally Bonded to Concrete under Cyclic Loading.

PubMed

Li, Ke; Cao, Shuangyin; Yang, Yue; Zhu, Juntao

2018-02-26

The objective of this paper was to explore the bond-slip relationship between carbon fiber-reinforced polymer (CFRP) sheets and concrete under cyclic loading through experimental and analytical approaches. Modified beam tests were performed in order to gain insight into the bond-slip relationship under static and cyclic loading. The test variables are the CFRP-to-concrete width ratio, and the bond length of the CFRP sheets. An analysis of the test results in this paper and existing test results indicated that the slope of the ascending segment of the bond-slip curve decreased with an increase in the number of load cycles, but the slip corresponding to the maximum shear stress was almost invariable as the number of load cycles increased. In addition, the rate of reduction in the slope of the ascending range of the bond-slip curve during cyclic loading decreased as the concrete strength increased, and increased as the load level or CFRP-to-concrete width ratio enhanced. However, these were not affected by variations in bond length if the residual bond length was longer than the effective bond length. A bilinear bond-slip model for CFRP sheets that are externally bonded to concrete under cyclic loading, which considered the effects of the cyclic load level, concrete strength, and CFRP-to-concrete ratio, was developed based on the existing static bond-slip model. The accuracy of this proposed model was verified by a comparison between this proposed model and test results.

Fluid Pressures at the Shoe-Floor-Contaminant Interface During Slips: Effects of Tread & Implications on Slip Severity

PubMed Central

Beschorner, Kurt E.; Albert, Devon L.; Chambers, April J.; Redfern, Mark S.

2018-01-01

Previous research on slip and fall accidents has suggested that pressurized fluid between the shoe and floor is responsible for initiating slips yet this effect has not been verified experimentally. This study aimed to 1) measure hydrodynamic pressures during slipping for treaded and untreaded conditions; 2) determine the effects of fluid pressure on slip severity; and 3) quantify how fluid pressures vary with instantaneous resultant slipping speed, position on the shoe surface, and throughout the progression of the slip. Eighteen subjects walked on known dry and unexpected slippery floors, while wearing treaded and untreaded shoes. Fluid pressure sensors, embedded in the floor, recorded hydrodynamic pressures during slipping. The maximum fluid pressures (mean+/−standard deviation) were significantly higher for the untreaded conditions (124 +/−75 kPa) than the treaded conditions (1.1 +/−0.29 kPa). Maximum fluid pressures were positively correlated with peak slipping speed (r = 0.87), suggesting that higher fluid pressures, which are associated with untreaded conditions, resulted in more severe slips. Instantaneous resultant slipping speed and position of sensor relative to the shoe sole and walking direction explained 41% of the fluid pressure variability. Fluid pressures were primarily observed for untreaded conditions. This study confirms that fluid pressures are relevant to slipping events, consistent with fluid dynamics theory (i.e. the Reynolds equation), and can be modified with shoe tread design. The results suggest that the occurrence and severity of unexpected slips can be reduced by designing shoes/floors that reduce underfoot fluid pressures. PMID:24267270

New seismic sources parameterization in El Salvador. Implications to seismic hazard.

NASA Astrophysics Data System (ADS)

Alonso-Henar, Jorge; Staller, Alejandra; Jesús Martínez-Díaz, José; Benito, Belén; Álvarez-Gómez, José Antonio; Canora, Carolina

2014-05-01

El Salvador is located at the pacific active margin of Central America, here, the subduction of the Cocos Plate under the Caribbean Plate at a rate of ~80 mm/yr is the main seismic source. Although the seismic sources located in the Central American Volcanic Arc have been responsible for some of the most damaging earthquakes in El Salvador. The El Salvador Fault Zone is the main geological structure in El Salvador and accommodates 14 mm/yr of horizontal displacement between the Caribbean Plate and the forearc sliver. The ESFZ is a right lateral strike-slip fault zone c. 150 km long and 20 km wide .This shear band distributes the deformation among strike-slip faults trending N90º-100ºE and secondary normal faults trending N120º- N170º. The ESFZ is relieved westward by the Jalpatagua Fault and becomes less clear eastward disappearing at Golfo de Fonseca. Five sections have been proposed for the whole fault zone. These fault sections are (from west to east): ESFZ Western Section, San Vicente Section, Lempa Section, Berlin Section and San Miguel Section. Paleoseismic studies carried out in the Berlin and San Vicente Segments reveal an important amount of quaternary deformation and paleoearthquakes up to Mw 7.6. In this study we present 45 capable seismic sources in El Salvador and their preliminary slip-rate from geological and GPS data. The GPS data detailled results are presented by Staller et al., 2014 in a complimentary communication. The calculated preliminary slip-rates range from 0.5 to 8 mm/yr for individualized faults within the ESFZ. We calculated maximum magnitudes from the mapped lengths and paleoseismic observations.We propose different earthquakes scenario including the potential combined rupture of different fault sections of the ESFZ, resulting in maximum earthquake magnitudes of Mw 7.6. We used deterministic models to calculate acceleration distribution related with maximum earthquakes of the different proposed scenario. The spatial distribution of seismic accelerations are compared and calibrated using the February 13, 2001 earthquake, as control earthquake. To explore the sources of historical earthquakes we compare synthetic acceleration maps with the historical earthquakes of March 6, 1719 and June 8, 1917. control earthquake. To explore the sources of historical earthquakes we compare synthetic acceleration maps with the historical earthquakes of March 6, 1719 and June 8, 1917.

Stressing of the New Madrid seismic zone by a lower crust detachment fault

USGS Publications Warehouse

Stuart, W.D.; Hildenbrand, T.G.; Simpson, R.W.

1997-01-01

A new mechanical model for the cause of the New Madrid seismic zone in the central United States is analyzed. The model contains a subhorizontal detachment fault which is assumed to be near the domed top surface of locally thickened anomalous lower crust ("rift pillow"). Regional horizontal compression induces slip on the fault, and the slip creates a stress concentration in the upper crust above the rift pillow dome. In the coseismic stage of the model earthquake cycle, where the three largest magnitude 7-8 earthquakes in 1811-1812 are represented by a single model mainshock on a vertical northeast trending fault, the model mainshock has a moment equivalent to a magnitude 8 event. During the interseismic stage, corresponding to the present time, slip on the detachment fault exerts a right-lateral shear stress on the locked vertical fault whose failure produces the model mainshock. The sense of shear is generally consistent with the overall sense of slip of 1811-1812 and later earthquakes. Predicted rates of horizontal strain at the ground surface are about 10-7 year-1 and are comparable to some observed rates. The model implies that rift pillow geometry is a significant influence on the maximum possible earthquake magnitude.

Investigations into the Fish Lake Valley Fault Zone (FLVFZ) and its interactions with normal faulting within Eureka and Deep Springs Valleys

NASA Astrophysics Data System (ADS)

Lawson, M. J.; Rhodes, E.; Yin, A.

2016-12-01

In most textbooks, the San Andreas Fault is stated to be the plate boundary between the North American and the Pacific plates, as plate tectonics assumes that boundaries are essentially discrete. In the Western United States this is not the case, as up to 25% of relative plate motion is accommodated on other structures within the Walker Lane Shear Zone (WLSZ) in a diffuse 100 km margin (Faulds et al., 2005; Oldow et al., 2001). Fish Lake Valley Fault Zone (FLVFZ), situated at the northern border of Death Valley National Park, is the northern continuation of the Furnace Creek Fault Zone (FCFZ), and is an important transfer structure within the Walker Lane Shear Zone. Though the FLVFZ has a long term rate (since 10 Ma) of 5 mm/yr (Reheis and Sawyer, 1997), it has a highly variable slip rate. In the middle Pleistocene, the rate has a maximum of up to 11 mm/yr which would accommodate nearly the entirety of slip within the Walker Lane, and yet this rate decreases significantly ( 2.5 to 3 mm/yr) by the late Pleistocene due to unknown causes (Frankel et al. 2007). This variation in slip rate has been proposed by previous workers to be due to strain transience, an increase in the overall strain rate, or due to other unknown structures (Lee et al., 2009). Currently, we are investigating the cause of this variation, and the possibility of the transfer of slip to faults south of the FLVFZ on oblique normal faults within Eureka and Deep Springs Valleys. Preliminary data will be shown utilizing scarp transects, geomorphic scarp modeling, and Optically Stimulated Luminescence (OSL) dating techniques.

Quaternary Activity of the Monastir and Grombalia Fault Systems in the North‒Eastern Tunisia (Seismotectonic Implication)

NASA Astrophysics Data System (ADS)

Ghribi, R.; Zaatra, D.; Bouaziz, S.

2018-01-01

The Monastir and Grombalia fault systems consist of three strands that the northern segment corresponds to Hammamet and Grombalia faults. The southern strand represents Monastir Fault also referred to as the Skanes-Khnis Fault. These NW-trends are observed continuously in the major outcropping features of north-eastern Tunisia including both the Cap Bon peninsula and the Sahel domain. Along the Hammamet Fault, the north-eastern strand of Grombalia fault system, left lateral drainage offset of amount 220 m is found in Fawara valley. To the South, the left lateral movement is occurred along the Monastir Fault based on 180 m of Tyrrhenian terrace displacement. Field observations supported by satellite images suggest that the Monastir and Grombalia fault systems appear to slip mostly laterally with components of normal dip slip. Assuming the development of the stream networks during the Riss-Würm interglacial (115000-125000 years) and the age of the Tyrrhenian terrace (121 ± 10 ka), the strike slip rates of the Hammamet and Monastir faults are calculated in the range of 1.5-1.8 mm/yr. There vertical slip rates are estimated to be 0.06 and 0.26 mm/yr, respectively. These data are consistent with the displacement rate in the Pelagian shelf (1-2 mm/yr) but they are below the convergence rate of African-Eurasian plates (8 mm/yr). Our seismotectonics study reveals that a maximum earthquake of Mw = 6.5 could occur every 470 years in the Hammamet fault zone and Mw = 6-every 263 years in the Monastir fault zone.

Joint inversion of GNSS and teleseismic data for the rupture process of the 2017 M w6.5 Jiuzhaigou, China, earthquake

NASA Astrophysics Data System (ADS)

Li, Qi; Tan, Kai; Wang, Dong Zhen; Zhao, Bin; Zhang, Rui; Li, Yu; Qi, Yu Jie

2018-02-01

The spatio-temporal slip distribution of the earthquake that occurred on 8 August 2017 in Jiuzhaigou, China, was estimated from the teleseismic body wave and near-field Global Navigation Satellite System (GNSS) data (coseismic displacements and high-rate GPS data) based on a finite fault model. Compared with the inversion results from the teleseismic body waves, the near-field GNSS data can better restrain the rupture area, the maximum slip, the source time function, and the surface rupture. The results show that the maximum slip of the earthquake approaches 1.4 m, the scalar seismic moment is 8.0 × 1018 N·m (M w ≈ 6.5), and the centroid depth is 15 km. The slip is mainly driven by the left-lateral strike-slip and it is initially inferred that the seismogenic fault occurs in the south branch of the Tazang fault or an undetectable fault, a NW-trending left-lateral strike-slip fault, and belongs to one of the tail structures at the easternmost end of the eastern Kunlun fault zone. The earthquake rupture is mainly concentrated at depths of 5-15 km, which results in the complete rupture of the seismic gap left by the previous four earthquakes with magnitudes > 6.0 in 1973 and 1976. Therefore, the possibility of a strong aftershock on the Huya fault is low. The source duration is 30 s and there are two major ruptures. The main rupture occurs in the first 10 s, 4 s after the earthquake; the second rupture peak arrives in 17 s. In addition, the Coulomb stress study shows that the epicenter of the earthquake is located in the area where the static Coulomb stress change increased because of the 12 May 2017 M w7.9 Wenchuan, China, earthquake. Therefore, the Wenchuan earthquake promoted the occurrence of the 8 August 2017 Jiuzhaigou earthquake.

Joint inversion of GNSS and teleseismic data for the rupture process of the 2017 M w6.5 Jiuzhaigou, China, earthquake

NASA Astrophysics Data System (ADS)

Li, Qi; Tan, Kai; Wang, Dong Zhen; Zhao, Bin; Zhang, Rui; Li, Yu; Qi, Yu Jie

2018-05-01

The spatio-temporal slip distribution of the earthquake that occurred on 8 August 2017 in Jiuzhaigou, China, was estimated from the teleseismic body wave and near-field Global Navigation Satellite System (GNSS) data (coseismic displacements and high-rate GPS data) based on a finite fault model. Compared with the inversion results from the teleseismic body waves, the near-field GNSS data can better restrain the rupture area, the maximum slip, the source time function, and the surface rupture. The results show that the maximum slip of the earthquake approaches 1.4 m, the scalar seismic moment is 8.0 × 1018 N·m ( M w ≈ 6.5), and the centroid depth is 15 km. The slip is mainly driven by the left-lateral strike-slip and it is initially inferred that the seismogenic fault occurs in the south branch of the Tazang fault or an undetectable fault, a NW-trending left-lateral strike-slip fault, and belongs to one of the tail structures at the easternmost end of the eastern Kunlun fault zone. The earthquake rupture is mainly concentrated at depths of 5-15 km, which results in the complete rupture of the seismic gap left by the previous four earthquakes with magnitudes > 6.0 in 1973 and 1976. Therefore, the possibility of a strong aftershock on the Huya fault is low. The source duration is 30 s and there are two major ruptures. The main rupture occurs in the first 10 s, 4 s after the earthquake; the second rupture peak arrives in 17 s. In addition, the Coulomb stress study shows that the epicenter of the earthquake is located in the area where the static Coulomb stress change increased because of the 12 May 2017 M w7.9 Wenchuan, China, earthquake. Therefore, the Wenchuan earthquake promoted the occurrence of the 8 August 2017 Jiuzhaigou earthquake.

The finite, kinematic rupture properties of great-sized earthquakes since 1990

USGS Publications Warehouse

Hayes, Gavin

2017-01-01

Here, I present a database of >160 finite fault models for all earthquakes of M 7.5 and above since 1990, created using a consistent modeling approach. The use of a common approach facilitates easier comparisons between models, and reduces uncertainties that arise when comparing models generated by different authors, data sets and modeling techniques.I use this database to verify published scaling relationships, and for the first time show a clear and intriguing relationship between maximum potency (the product of slip and area) and average potency for a given earthquake. This relationship implies that earthquakes do not reach the potential size given by the tectonic load of a fault (sometimes called “moment deficit,” calculated via a plate rate over time since the last earthquake, multiplied by geodetic fault coupling). Instead, average potency (or slip) scales with but is less than maximum potency (dictated by tectonic loading). Importantly, this relationship facilitates a more accurate assessment of maximum earthquake size for a given fault segment, and thus has implications for long-term hazard assessments. The relationship also suggests earthquake cycles may not completely reset after a large earthquake, and thus repeat rates of such events may appear shorter than is expected from tectonic loading. This in turn may help explain the phenomenon of “earthquake super-cycles” observed in some global subduction zones.

The finite, kinematic rupture properties of great-sized earthquakes since 1990

NASA Astrophysics Data System (ADS)

Hayes, Gavin P.

2017-06-01

Here, I present a database of >160 finite fault models for all earthquakes of M 7.5 and above since 1990, created using a consistent modeling approach. The use of a common approach facilitates easier comparisons between models, and reduces uncertainties that arise when comparing models generated by different authors, data sets and modeling techniques. I use this database to verify published scaling relationships, and for the first time show a clear and intriguing relationship between maximum potency (the product of slip and area) and average potency for a given earthquake. This relationship implies that earthquakes do not reach the potential size given by the tectonic load of a fault (sometimes called ;moment deficit,; calculated via a plate rate over time since the last earthquake, multiplied by geodetic fault coupling). Instead, average potency (or slip) scales with but is less than maximum potency (dictated by tectonic loading). Importantly, this relationship facilitates a more accurate assessment of maximum earthquake size for a given fault segment, and thus has implications for long-term hazard assessments. The relationship also suggests earthquake cycles may not completely reset after a large earthquake, and thus repeat rates of such events may appear shorter than is expected from tectonic loading. This in turn may help explain the phenomenon of ;earthquake super-cycles; observed in some global subduction zones.

Behavior of aircraft antiskid braking systems on dry and wet runway surfaces - A velocity-rate-controlled, pressure-bias-modulated system

NASA Technical Reports Server (NTRS)

Stubbs, S. M.; Tanner, J. A.

1976-01-01

During maximum braking the average ratio of drag-force friction coefficient developed by the antiskid system to maximum drag-force friction coefficient available at the tire/runway interface was higher on dry surfaces than on wet surfaces. The gross stopping power generated by the brake system on the dry surface was more than twice that obtained on the wet surfaces. With maximum braking applied, the average ratio of side-force friction coefficient developed by the tire under antiskid control to maximum side-force friction available at the tire/runway interface of a free-rolling yawed tire was shown to decrease with increasing yaw angle. Braking reduced the side-force friction coefficient on a dry surface by 75 percent as the wheel slip ratio was increased to 0.3; on a flooded surface the coefficient dropped to near zero for the same slip ratio. Locked wheel skids were observed when the tire encountered a runway surface transition from dry to flooded, due in part to the response time required for the system to sense abrupt changes in the runway friction; however, the antiskid system quickly responded by reducing brake pressure and cycling normally during the remainder of the run on the flooded surface.

Joint Inversion of 1-Hz GPS Data and Strong Motion Records for the Rupture Process of the 2008 Iwate-Miyagi Nairiku Earthquake: Objectively Determining Relative Weighting

NASA Astrophysics Data System (ADS)

Wang, Z.; Kato, T.; Wang, Y.

2015-12-01

The spatiotemporal fault slip history of the 2008 Iwate-Miyagi Nairiku earthquake, Japan, is obtained by the joint inversion of 1-Hz GPS waveforms and near-field strong motion records. 1-Hz GPS data from GEONET is processed by GAMIT/GLOBK and then a low-pass filter of 0.05 Hz is applied. The ground surface strong motion records from stations of K-NET and Kik-Net are band-pass filtered for the range of 0.05 ~ 0.3 Hz and integrated once to obtain velocity. The joint inversion exploits a broader frequency band for near-field ground motions, which provides excellent constraints for both the detailed slip history and slip distribution. A fully Bayesian inversion method is performed to simultaneously and objectively determine the rupture model, the unknown relative weighting of multiple data sets and the unknown smoothing hyperparameters. The preferred rupture model is stable for different choices of velocity structure model and station distribution, with maximum slip of ~ 8.0 m and seismic moment of 2.9 × 1019 Nm (Mw 6.9). By comparison with the single inversion of strong motion records, the cumulative slip distribution of joint inversion shows sparser slip distribution with two slip asperities. One common slip asperity extends from the hypocenter southeastward to the ground surface of breakage; another slip asperity, which is unique for joint inversion contributed by 1-Hz GPS waveforms, appears in the deep part of fault where very few aftershocks are occurring. The differential moment rate function of joint and single inversions obviously indicates that rich high frequency waves are radiated in the first three seconds but few low frequency waves.

The Architecture and Frictional Properties of Faults in Shale

NASA Astrophysics Data System (ADS)

De Paola, N.; Imber, J.; Murray, R.; Holdsworth, R.

2015-12-01

The geometry of brittle fault zones in shale rocks, as well as their frictional properties at reservoir conditions, are still poorly understood. Nevertheless, these factors may control the very low recovery factors (25% for gas and 5% for oil) obtained during fracking operations. Extensional brittle fault zones (maximum displacement < 3 m) cut exhumed oil mature black shales in the Cleveland Basin (UK). Fault cores up to 50 cm wide accommodated most of the displacement, and are defined by a stair-step geometry. Their internal architecture is characterised by four distinct fault rock domains: foliated gouges; breccias; hydraulic breccias; and a slip zone up to 20 mm thick, composed of a fine-grained black gouge. Hydraulic breccias are located within dilational jogs with aperture of up to 20 cm. Brittle fracturing and cataclastic flow are the dominant deformation mechanisms in the fault core of shale faults. Velocity-step and slide-hold-slide experiments at sub-seismic slip rates (microns/s) were performed in a rotary shear apparatus under dry, water and brine-saturated conditions, for displacements of up to 46 cm. Both the protolith shale and the slip zone black gouge display shear localization, velocity strengthening behaviour and negative healing rates, suggesting that slow, stable sliding faulting should occur within the protolith rocks and slip zone gouges. Experiments at seismic speed (1.3 m/s), performed on the same materials under dry conditions, show that after initial friction values of 0.5-0.55, friction decreases to steady-state values of 0.1-0.15 within the first 10 mm of slip. Contrastingly, water/brine saturated gouge mixtures, exhibit almost instantaneous attainment of very low steady-state sliding friction (0.1), suggesting that seismic ruptures may efficiently propagate in the slip zone of fluid-saturated shale faults. Stable sliding in faults in shale can cause slow fault/fracture propagation, affecting the rate at which new fracture areas are created and, hence, limiting oil and gas production during reservoir stimulation. However, fluid saturated conditions can favour seismic slip propagation, with fast and efficient creation of new fracture areas. These processes are very effective at dilational jogs, where fluid circulation may be enhanced, facilitating oil and gas production.

Spatial and temporal patterns of fault creep across an active salt system, Canyonlands National Park, Utah

NASA Astrophysics Data System (ADS)

Kravitz, K.; Mueller, K. J.; Furuya, M.; Tiampo, K. F.

2017-12-01

First order conditions that control creeping behavior on faults include the strength of faulted materials, fault maturity and stress changes associated with seismic cycles. We present mapping of surface strain from differential interferometric synthetic aperture radar (DInSAR) of actively creeping faults in Eastern Utah that form by reactivation of older joints and faults. A nine-year record of displacement across the region using descending ERS scenes from 1992-2001 suggests maximum slip rates of 1 mm/yr. Time series analysis shows near steady rates across the region consistent with the proposed ultra-weak nature of these faults as suggested by their dilating nature, based on observations of sinkholes, pit chains and recently opened fissures along their lengths. Slip rates along the faults in the main part of the array are systematically faster with closer proximity to the Colorado River Canyon, consistent with mechanical modeling of the boundary conditions that control the overall salt system. Deeply incised side tributaries coincide with and control the edges of the region with higher strain rates. Comparison of D:L scaling at decadal scales in fault bounded grabens (as defined by InSAR) with previous measurements of total slip (D) to length (L) is interpreted to suggest that faults reached nearly their current lengths relatively quickly (i.e. displaying low displacement to length scaling). We argue this may then have been followed by along strike slip distributions where the centers of the grabens slip more rapidly than their endpoints, resulting in a higher D:L ratio over time. InSAR mapping also points to an increase in creep rates in overlap zones where two faults became hard-linked at breached relay ramps. Additionally, we see evidence for soft-linkage, where displacement profiles along a graben coincide with obvious fault segments. While an endmember case (ultra-weak faults sliding above a plastic substrate), structures in this region highlight mechanical behavior driven by rheological conditions that promote steady state slip in a complex array of extensional faults. Besides defining how creep varies along strike on individual faults, our work also hints at how strain rates may vary within the context of ongoing strain and fault linkage in a complex fault array.

Interseismic Deformation on the San Andreas Fault System

NASA Astrophysics Data System (ADS)

Segall, P.

2001-12-01

Interseismic deformation measurements are most often interpreted in terms of steady slip on buried elastic dislocations. While such models often yield slip-rates that are in reasonable accord with geologic observations, they are: 1) inconsistent with observations of transient deformation following large earthquakes, and 2) tend to predict locking depths significantly deeper than recent large earthquakes. An alternate two-dimensional model of repeating earthquakes that break an elastic plate of thickness H, overlying a viscoelastic half-space with relaxation time tR (Savage and Prescott, 1978) involves 5 parameters; H, tR, t, T, and ˙ {s}, where t is the time since the last quake, T is the earthquake cycle time, and ˙ {s} is the slip-rate. Many parts of the SAF system involve multiple parallel faults, which further increases the number of parameters to be estimated. All hope is not lost, however, if we make use of a priori constraints on slip-rate from geologic studies, and utilize measurements of time dependent strain following the 1906 earthquake, in addition to the present day spatial distribution of deformation-rate. GPS data from the Carrizo Plain segment of the SAF imply a considerably larger relaxation time than inferred from the post-1906 strain-rate transient. This indicates that either the crustal structure differs significantly between northern and central California, or that the simple model is deficient, either due to time-dependent down-dip slip following large earthquakes or non-linear rheology. To test the effect of regional variations in H and tR, I analyze data from the northern San Francisco Bay area (Prescott et al, 2001, JGR), and include the SAF, the Hayward-Rogers Creek (HRC), and Concord-Green Valley faults (CGV). Non-linear optimization using simulated annealing and constrained non-linear least squares yields an optimal model with: H ~ 10 km, tR ~ 34 years, TSAF = 205 years, ˙ {s}SAF ~ 18 mm/yr, tHRC = 225 years, T{ HRC} = 630 years, and ˙ {s}{HRC } ~ 13 mm/yr, ˙ {s}CGV ~ 9 mm/yr. Adding the constraint that the coseismic slip in major Hayward and San Andreas events not exceed 3.0 m and 7.0 m, respectively yields an optimal model with: H ~ 18 km, tR ~ 36 years, TSAF = 280 years, ˙ {s}SAF = 25 mm/yr, tHRC = 225 years, T{ HRC} = 276 years, and ˙ {s}{HRC } ~ 11 mm/yr, ˙ {s}CGV ~ 9 mm/yr. These estimates are in reasonable accord with independent paleoseismic results. The conclusion of this pilot study is that by combining the present day deformation field, post-1906 strain data, and geologic bounds on slip-rate and maximum earthquake slip, we can estimate parameters of considerable geophysical interest, including time since past quakes and average recurrence interval.

Block modeling of crustal deformation in Tierra del Fuego from GNSS velocities

NASA Astrophysics Data System (ADS)

Mendoza, L.; Richter, A.; Fritsche, M.; Hormaechea, J. L.; Perdomo, R.; Dietrich, R.

2015-05-01

The Tierra del Fuego (TDF) main island is divided by a major transform boundary between the South America and Scotia tectonic plates. Using a block model, we infer slip rates, locking depths and inclinations of active faults in TDF from inversion of site velocities derived from Global Navigation Satellite System observations. We use interseismic velocities from 48 sites, obtained from field measurements spanning 20 years. Euler vectors consistent with a simple seismic cycle are estimated for each block. In addition, we introduce far-field information into the modeling by applying constraints on Euler vectors of major tectonic plates. The difference between model and observed surface deformation near the Magallanes Fagnano Fault System (MFS) is reduced by considering finite dip in the forward model. For this tectonic boundary global plate circuits models predict relative movements between 7 and 9 mm yr- 1, while our regional model indicates that a strike-slip rate of 5.9 ± 0.2 mm yr- 1 is accommodated across the MFS. Our results indicate faults dipping 66- 4+ 6° southward, locked to a depth of 11- 5+ 5 km, which are consistent with geological models for the MFS. However, normal slip also dominates the fault perpendicular motion throughout the eastern MFS, with a maximum rate along the Fagnano Lake.

Trench investigation along the Merida section of the Bocono fault (central Venezuelan Andes), Venezuela

USGS Publications Warehouse

Audemard, F.; Pantosti, D.; Machette, M.; Costa, C.; Okumura, K.; Cowan, H.; Diederix, H.; Ferrer, C.

1999-01-01

The Bocono fault is a major NE-SW-trending, dextral fault that extends for about 500 km along the backbone of the Venezuelan Andes. Several large historical earthquakes in this region have been attributed to the Bocono fault, and some of these have been recently associated with specific parts through paleoseismologic investigations. A new trench study has been performed, 60 km to the northeast of Merida in the central Venezuelan Andes, where the fault forms a releasing bend, comprising two conspicuous late Holocene fault strands that are about 1 km apart. The southern and northern strands carry about 70% and 30% (respectively) of the 7-10 mm/yr net slip rate measured in this sector, which is based on a 40 vs. 85-100 m right-lateral offset of the Late Pleistocene Los Zerpa moraines. A trench excavated on the northern strand of the fault (near Morros de los Hoyos, slightly northeast of Apartaderos) across a twin shutter ridge and related sag pond exposed two main fault zones cutting Late Pleistocene alluvial and Holocene peat deposits. Each zone forms a shutter ridge with peat deposits ponded against the uplifted block. The paleoearthquake reconstruction derived from this trench allow us to propose the occurrence of at least 6-8 earthquakes in the past 9000 yr, yielding a maximum average recurrence interval of about 1100-1500 yr. Based on the northern strands average slip rate (2.6 mm/yr), such as earthquake sequence should have accommodated about 23 m of slip since 9 ka, suggesting that the maximum slip per event ranges between 3 and 4 m. No direct evidence for the large 1812 earthquake has been found in the trench, although this earthquake may have ruptured this section of the fault. Further paleoseismic studies will investigate the possibility that this event occurred in the Bocono fault, but ruptured mainly its southern strand in this region.

Strain partitioning in southeastern Alaska: Is the Chatham Strait Fault active?

USGS Publications Warehouse

Brothers, Daniel; Elliott, Julie L.; Conrad, James E.; Haeussler, Peter J.; Kluesner, Jared

2018-01-01

A 1200 km-long transform plate boundary passes through southeastern Alaska and northwestern British Columbia and represents one of the most seismically active, but poorly understood continental margins of North America. Although most of the plate motion is accommodated by the right-lateral Queen Charlotte–Fairweather Fault (QCFF) System, which has produced at least six M > 7 earthquakes since 1920, seismic hazard assessments also include the Chatham Strait Fault (CSF) as a potentially active, 400 km-long strike slip fault that cuts northward through southeastern Alaska, connecting with the Eastern Denali Fault. Nearly the entire length of the CSF is submerged beneath Chatham Strait and Lynn Canal and has never been systematically imaged using high-resolution marine geophysical approaches. In this study we present an integrated analysis of new marine seismic reflectiondata acquired across Lynn Canal and tectonic block modeling constrained by data from continuous and campaign GPS sites. Seismic profiles cross the CSF at twelve locations spanning ∼50 km of fault length; they reveal thick (up to 300 m) packages of glaciomarine sedimentary facies emplaced on an unconformity surface that formed during the Last Glacial Maximum (LGM). Localized warping of post-LGM stratigraphy (∼13.9 kyr B.P. to present) appears to correlate with sediment drape on basement topography and current-controlled deposition. There is no evidence for an active fault along the axis of Lynn Canal in the seismic reflection data. Crustal block models constrained by GPS data allow, but do not require, a maximum slip rate of 2–3 mm/yr along the CSF; higher slip rates on the CSF result in significant misfit to GPS data in the surrounding region. Based on the combined marine geophysical and GPS observations, it is plausible that the CSF has not generated resolvable coseismic deformation in the last ∼13 ka and that the modern slip-rate is <1 mm/yr. We propose that models for strain transfer between the QCFF and the Denali Fault, and seismic hazard maps in general, may need to be reevaluated.

Strain partitioning in Southeastern Alaska: Is the Chatham Strait Fault active?

NASA Astrophysics Data System (ADS)

Brothers, Daniel S.; Elliott, Julie L.; Conrad, James E.; Haeussler, Peter J.; Kluesner, Jared W.

2018-01-01

A 1200 km-long transform plate boundary passes through southeastern Alaska and northwestern British Columbia and represents one of the most seismically active, but poorly understood continental margins of North America. Although most of the plate motion is accommodated by the right-lateral Queen Charlotte-Fairweather Fault (QCFF) System, which has produced at least six M > 7 earthquakes since 1920, seismic hazard assessments also include the Chatham Strait Fault (CSF) as a potentially active, 400 km-long strike slip fault that cuts northward through southeastern Alaska, connecting with the Eastern Denali Fault. Nearly the entire length of the CSF is submerged beneath Chatham Strait and Lynn Canal and has never been systematically imaged using high-resolution marine geophysical approaches. In this study we present an integrated analysis of new marine seismic reflection data acquired across Lynn Canal and tectonic block modeling constrained by data from continuous and campaign GPS sites. Seismic profiles cross the CSF at twelve locations spanning ∼50 km of fault length; they reveal thick (up to 300 m) packages of glaciomarine sedimentary facies emplaced on an unconformity surface that formed during the Last Glacial Maximum (LGM). Localized warping of post-LGM stratigraphy (∼13.9 kyr B.P. to present) appears to correlate with sediment drape on basement topography and current-controlled deposition. There is no evidence for an active fault along the axis of Lynn Canal in the seismic reflection data. Crustal block models constrained by GPS data allow, but do not require, a maximum slip rate of 2-3 mm/yr along the CSF; higher slip rates on the CSF result in significant misfit to GPS data in the surrounding region. Based on the combined marine geophysical and GPS observations, it is plausible that the CSF has not generated resolvable coseismic deformation in the last ∼13 ka and that the modern slip-rate is <1 mm/yr. We propose that models for strain transfer between the QCFF and the Denali Fault, and seismic hazard maps in general, may need to be reevaluated.

Spatially varying stress state in the central U.S. from joint inversion of focal mechanism and maximum horizontal stress data

NASA Astrophysics Data System (ADS)

Carlson, G.; Johnson, K. M.; Rupp, J. A.

2017-12-01

The Midcontinental United States continues to experience anomalously high rates of seismicity and generate large earthquakes despite its location in the cratonic interior, far from any plate boundary. There is renewed interest in Midcontinent seismicity with the concern that fluid injection within the Illinois basin could induce seismicity. In order to better understand the seismic hazard and inform studies of risk mitigation, we present an assessment of the contemporary crustal stress state in the Illinois basin and surrounding region, looking specifically at how the orientation of maximum horizontal compressive stress varies throughout the region. This information will help identify which faults are critically stressed and therefore most likely to fail under increased pore pressures. We conduct a Bayesian stress inversion of focal mechanism solutions and maximum horizontal stress orientations from borehole breakout, core fracture, overcoring, hydraulic fracture, and strain gauge measurements for maximum horizontal compressive stress orientations across the Midcontinent region and produce a map of expected faulting styles. Because distinguishing the slipping fault plane from the auxiliary nodal plane is ambiguous for focal mechanisms, the choice of the fault plane and associated slip vector to use in the inversion is important in the estimation of the stress tensor. The stress inversion provides an objective means to estimate nonlinear parameters including the spatial smoothing parameter, unknown data uncertainties, as well as the selection of focal mechanism nodal planes. We find a systematic rotation of the maximum horizontal stress orientation (SHmax) across a 1000 km width of the Midcontinent. We find that SHmax rotates from N60E to E/W orientation across the southern Illinois basin and returns to N60E in the western Appalachian basin. The stress regime is largely consistent with strike-slip faulting with pockets of a reverse-faulting stress regime near the New Madrid and Wabash Valley seismic zones.

Co-seismic ruptures of the 12 May 2008, Ms 8.0 Wenchuan earthquake, Sichuan: East-west crustal shortening on oblique, parallel thrusts along the eastern edge of Tibet

USGS Publications Warehouse

Liu-Zeng, J.; Zhang, Z.; Wen, L.; Tapponnier, P.; Sun, Jielun; Xing, X.; Hu, G.; Xu, Q.; Zeng, L.; Ding, L.; Ji, C.; Hudnut, K.W.; van der Woerd, J.

2009-01-01

The Ms 8.0, Wenchuan earthquake, which devastated the mountainous western rim of the Sichuan basin in central China, produced a surface rupture over 200??km-long with oblique thrust/dextral slip and maximum scarp heights of ~ 10??m. It thus ranks as one of the world's largest continental mega-thrust events in the last 150??yrs. Field investigation shows clear surface breaks along two of the main branches of the NE-trending Longmen Shan thrust fault system. The principal rupture, on the NW-dipping Beichuan fault, displays nearly equal amounts of thrust and right-lateral slip. Basin-ward of this rupture, another continuous surface break is observed for over 70??km on the parallel, more shallowly NW-dipping Pengguan fault. Slip on this latter fault was pure thrusting, with a maximum scarp height of ~ 3.5??m. This is one of the very few reported instances of crustal-scale co-seismic slip partitioning on parallel thrusts. This out-of-sequence event, with distributed surface breaks on crustal mega-thrusts, highlights regional, ~ EW-directed, present day crustal shortening oblique to the Longmen Shan margin of Tibet. The long rupture and large offsets with strong horizontal shortening that characterize the Wenchuan earthquake herald a re-evaluation of tectonic models anticipating little or no active shortening of the upper crust along this edge of the plateau, and require a re-assessment of seismic hazard along potentially under-rated active faults across the densely populated western Sichuan basin and mountains. ?? 2009 Elsevier B.V.

States of stress and slip partitioning in a continental scale strike-slip duplex: Tectonic and magmatic implications by means of finite element modeling

NASA Astrophysics Data System (ADS)

Iturrieta, Pablo Cristián; Hurtado, Daniel E.; Cembrano, José; Stanton-Yonge, Ashley

2017-09-01

Orogenic belts at oblique convergent subduction margins accommodate deformation in several trench-parallel domains, one of which is the magmatic arc, commonly regarded as taking up the margin-parallel, strike-slip component. However, the stress state and kinematics of volcanic arcs is more complex than usually recognized, involving first- and second-order faults with distinctive slip senses and mutual interaction. These are usually organized into regional scale strike-slip duplexes, associated with both long-term and short-term heterogeneous deformation and magmatic activity. This is the case of the 1100 km-long Liquiñe-Ofqui Fault System in the Southern Andes, made up of two overlapping margin-parallel master faults joined by several NE-striking second-order faults. We present a finite element model addressing the nature and spatial distribution of stress across and along the volcanic arc in the Southern Andes to understand slip partitioning and the connection between tectonics and magmatism, particularly during the interseismic phase of the subduction earthquake cycle. We correlate the dynamics of the strike-slip duplex with geological, seismic and magma transport evidence documented by previous work, showing consistency between the model and the inferred fault system behavior. Our results show that maximum principal stress orientations are heterogeneously distributed within the continental margin, ranging from 15° to 25° counter-clockwise (with respect to the convergence vector) in the master faults and 10-19° clockwise in the forearc and backarc domains. We calculate the stress tensor ellipticity, indicating simple shearing in the eastern master fault and transpressional stress in the western master fault. Subsidiary faults undergo transtensional-to-extensional stress states. The eastern master fault displays slip rates of 5 to 10 mm/yr, whereas the western and subsidiary faults show slips rates of 1 to 5 mm/yr. Our results endorse that favorably oriented subsidiary faults serve as magma pathways, particularly where they are close to the intersection with a master fault. Also, the slip of a fault segment is enhanced when an adjacent fault kinematics is superimposed on the regional tectonic loading. Hence, finite element models help to understand coupled tectonics and volcanic processes, demonstrating that geological and geophysical observations can be accounted for by a small number of key first order boundary conditions.

A Long-term Slip Model for the San Ramón Fault, Santiago de Chile, from Tectonically Reconcilable Boundary Conditions

NASA Astrophysics Data System (ADS)

Aron, F.; Estay, N.; Cembrano, J. M.; Yanez, G. A.

2016-12-01

We constructed a 3D Boundary Elements model simulating subduction of the Nazca plate underneath South America, from 29° to 38° S, to compute long-term surface deformation and slip rates on crustal faults imbedded in the upper-plate wedge of the Andean orogen. We tested our model on the San Ramón Fault (SRF), a major E-dipping, thrust structure limiting the western front of the Main Cordillera with surface expression along the entire, 40 km long, extension of the Santiago de Chile basin. Long-lived thrusting has produced more than 2 km of differential uplift of the mountains. Given its proximity to the country's largest city, this potentially seismogenic fault —dormant during historic times— has drawn increasing public attention. We used earthquake hypocenters captured over a one-year seismic deployment, 2D resistivity profiles, and published geologic cross-sections to determine the geometry of the SRF. The base of the lithosphere and plate interface surfaces were defined based on average Andean values and the Slab1.0 model. The simulation reproduces plate convergence and mechanic decoupling of the lithospheric plates across the subduction seismic cycle using mixed boundary conditions. Relative plate motion is achieved prescribing uniform, far-field horizontal displacement over the depth extension of both the oceanic and continental lithospheric plates. Long-term deformation is carried out in two steps. First, the modeled surfaces are allowed to slip freely emulating continuous slip on the subduction megathrust; subsequently, zero displacement is prescribed on the locking zone of the megathrust down to 40 km depth, while keeping the rest of the surfaces traction free, mimicking interseismic conditions. Long-term slip rate fields obtained for the SRF range between 0.1 and 1% the plate convergence rate, with maximum values near the surface. Interestingly, at an estimated 76-77 mm/yr relative plate motion velocity, those rates agree well with what has been reported on studies at one paleoseismic trench site across the fault. These results might contribute to determining possible seismic scenarios for Santiago but perhaps more importantly, our approach could be use in estimations of long-term slip rates and surface deformation due to other crustal structures with unknown displacement history.

Stick-slip as a monitor of rates, states and frictional properties along thrusts in sand wedges

NASA Astrophysics Data System (ADS)

Rosenau, Matthias; Santimano, Tasca; Ritter, Malte; Oncken, Onno

2014-05-01

We developed a sandbox setup which allows monitoring the push of the moving backwall indenting a layer of sand. Depending on the ratio between indenter compliancy versus strain weakening of the granular material, wedge deformation shows unstable slip marked by force drops of various sizes and at multiple temporal scales. Basically we observe long-period slip instabilities related to strain localization during the formation of new thrusts, intermediate-period slip instabilities related to reactivation of existing thrusts and short-period slip instabilities related to the stick-slip mechanism of slip accumulation along "seismic" faults. Observed stick-slip is characterized by highly correlated size and frequency ("regular stick-slip") and is sensitive to integrated normal load, slip rate and frictional properties along the active thrust(s). By independently constraining the frictional properties using a ring-shear tester, we infer the integrated normal loads on the active faults from the stick-slip events and benchmark the results against a model calculating the normal loads from the wedge geometry. This way we are able to monitor rates, states and frictional properties along thrusts in sand wedges at unprecedented detail. As an example of application, a kinematic analysis of the stick slip events in the sandbox demonstrates how slip rates along thrusts vary systematically within accretion cycles although the kinematic boundary condition is stationary. Accordingly transient fault slip rates may accelerate up to twice the long-term convergence rate during formation of new thrusts and decelerate in the post-thrust formation stage in a non-linear way. Applied to nature this suggests that fault slip rate variations at the thousand-year time scale might be attributable to the elasticity of plates and material weakening rather than changes in plate velocities.

Surface slip and off-fault deformation patterns in the 2013 MW 7.7 Balochistan, Pakistan earthquake: Implications for controls on the distribution of near-surface coseismic slip

NASA Astrophysics Data System (ADS)

Zinke, Robert; Hollingsworth, James; Dolan, James F.

2014-12-01

Comparison of 398 fault offsets measured by visual analysis of WorldView high-resolution satellite imagery with deformation maps produced by COSI-Corr subpixel image correlation of Landsat-8 and SPOT5 imagery reveals significant complexity and distributed deformation along the 2013 Mw 7.7 Balochistan, Pakistan earthquake. Average slip along the main trace of the fault was 4.2 m, with local maximum offsets up to 11.4 m. Comparison of slip measured from offset geomorphic features, which record localized slip along the main strand of the fault, to the total displacement across the entire width of the surface deformation zone from COSI-Corr reveals ˜45% off-fault deformation. While previous studies have shown that the structural maturity of the fault exerts a primary control on the total percentage of off-fault surface deformation, large along-strike variations in the percentage of strain localization observed in the 2013 rupture imply the influence of important secondary controls. One such possible secondary control is the type of near-surface material through which the rupture propagated. We therefore compared the percentage off-fault deformation to the type of material (bedrock, old alluvium, and young alluvium) at the surface and the distance of the fault to the nearest bedrock outcrop (a proxy for sediment thickness along this hybrid strike slip/reverse slip fault). We find significantly more off-fault deformation in younger and/or thicker sediments. Accounting for and predicting such off-fault deformation patterns has important implications for the interpretation of geologic slip rates, especially for their use in probabilistic seismic hazard assessments, the behavior of near-surface materials during coseismic deformation, and the future development of microzonation protocols for the built environment.

Normal-faulting slip maxima and stress-drop variability: a geological perspective

USGS Publications Warehouse

Hecker, S.; Dawson, T.E.; Schwartz, D.P.

2010-01-01

We present an empirical estimate of maximum slip in continental normal-faulting earthquakes and present evidence that stress drop in intraplate extensional environments is dependent on fault maturity. A survey of reported slip in historical earthquakes globally and in latest Quaternary paleoearthquakes in the Western Cordillera of the United States indicates maximum vertical displacements as large as 6–6.5 m. A difference in the ratio of maximum-to-mean displacements between data sets of prehistoric and historical earthquakes, together with constraints on bias in estimates of mean paleodisplacement, suggest that applying a correction factor of 1.4±0.3 to the largest observed displacement along a paleorupture may provide a reasonable estimate of the maximum displacement. Adjusting the largest paleodisplacements in our regional data set (~6 m) by a factor of 1.4 yields a possible upper-bound vertical displacement for the Western Cordillera of about 8.4 m, although a smaller correction factor may be more appropriate for the longest ruptures. Because maximum slip is highly localized along strike, if such large displacements occur, they are extremely rare. Static stress drop in surface-rupturing earthquakes in the Western Cordillera, as represented by maximum reported displacement as a fraction of modeled rupture length, appears to be larger on normal faults with low cumulative geologic displacement (<2 km) and larger in regions such as the Rocky Mountains, where immature, low-throw faults are concentrated. This conclusion is consistent with a growing recognition that structural development influences stress drop and indicates that this influence is significant enough to be evident among faults within a single intraplate environment.

Recent crustal movements in the Sierra Nevada-Walker lane region of California-Nevada: Part i, rate and style of deformation

USGS Publications Warehouse

Slemmons, D.B.; Wormer, D.V.; Bell, E.J.; Silberman, M.L.

1979-01-01

This review of geological, seismological, geochronological and paleobotanical data is made to compare historic and geologic rates and styles of deformation of the Sierra Nevada and western Basin and Range Provinces. The main uplift of this region began about 17 m.y. ago, with slow uplift of the central Sierra Nevada summit region at rates estimated at about 0.012 mm/yr and of western Basin and Range Province at about 0.01 mm/yr. Many Mesozoic faults of the Foothills fault system were reactivated with normal slip in mid-Tertiary time and have continued to be active with slow slip rates. Sparse data indicate acceleration of rates of uplift and faulting during the Late Cenozoic. The Basin and Range faulting appears to have extended westward during this period with a reduction in width of the Sierra Nevada. The eastern boundary zone of the Sierra Nevada has an irregular en-echelon pattern of normal and right-oblique faults. The area between the Sierra Nevada and the Walker Lane is a complex zone of irregular patterns of ho??rst and graben blocks and conjugate normal-to right- and left-slip faults of NW and NE trend, respectively. The Walker Lane has at least five main strands near Walker Lake, with total right-slip separation estimated at 48 km. The NE-trending left-slip faults are much shorter than the Walker Lane fault zone and have maximum separations of no more than a few kilometers. Examples include the 1948 and 1966 fault zone northeast of Truckee, California, the Olinghouse fault (Part III) and possibly the almost 200-km-long Carson Lineament. Historic geologic evidence of faulting, seismologic evidence for focal mechanisms, geodetic measurements and strain measurements confirm continued regional uplift and tilting of the Sierra Nevada, with minor internal local faulting and deformation, smaller uplift of the western Basin and Range Province, conjugate focal mechanisms for faults of diverse orientations and types, and a NS to NE-SW compression axis (??1) and an EW to NW-SE extension axis (??3). ?? 1979.

Slip and Dilation Tendency Anlysis of Neal Hot Springs Geothermal Area

DOE Data Explorer

Faulds, James E.

2013-12-31

Slip and Dilation Tendency in focus areas Critically stressed fault segments have a relatively high likelihood of acting as fluid flow conduits (Sibson, 1994). As such, the tendency of a fault segment to slip (slip tendency; Ts; Morris et al., 1996) or to dilate (dilation tendency; Td; Ferrill et al., 1999) provides an indication of which faults or fault segments within a geothermal system are critically stressed and therefore likely to transmit geothermal fluids. The slip tendency of a surface is defined by the ratio of shear stress to normal stress on that surface: Ts = τ / σn (Morris et al., 1996). Dilation tendency is defined by the stress acting normal to a given surface: Td = (σ1-σn) / (σ1-σ3) (Ferrill et al., 1999). Slip and dilation were calculated using 3DStress (Southwest Research Institute). Slip and dilation tendency are both unitless ratios of the resolved stresses applied to the fault plane by ambient stress conditions. Values range from a maximum of 1, a fault plane ideally oriented to slip or dilate under ambient stress conditions to zero, a fault plane with no potential to slip or dilate. Slip and dilation tendency values were calculated for each fault in the focus study areas at, McGinness Hills, Neal Hot Springs, Patua, Salt Wells, San Emidio, and Tuscarora on fault traces. As dip is not well constrained or unknown for many faults mapped in within these we made these calculations using the dip for each fault that would yield the maximum slip tendency or dilation tendency. As such, these results should be viewed as maximum tendency of each fault to slip or dilate. The resulting along-fault and fault-to-fault variation in slip or dilation potential is a proxy for along fault and fault-to-fault variation in fluid flow conduit potential. Stress Magnitudes and directions Stress field variation within each focus area was approximated based on regional published data and the world stress database (Hickman et al., 2000; Hickman et al., 1998 Robertson-Tait et al., 2004; Hickman and Davatzes, 2010; Davatzes and Hickman, 2006; Blake and Davatzes 2011; Blake and Davatzes, 2012; Moeck et al., 2010; Moos and Ronne, 2010 and Reinecker et al., 2005) as well as local stress information if applicable. For faults within these focus systems we applied either a normal faulting stress regime where the vertical stress (sv) is larger than the maximum horizontal stress (shmax) which is larger than the minimum horizontal stress (sv>shmax>shmin) or strike-slip faulting stress regime where the maximum horizontal stress (shmax) is larger than the vertical stress (sv) which is larger than the minimum horizontal stress (shmax >sv>shmin) depending on the general tectonic province of the system. Based on visual inspection of the limited stress magnitude data in the Great Basin we used magnitudes such that shmin/shmax = .527 and shmin/sv= .46, which are consistent with complete and partial stress field determinations from Desert Peak, Coso, the Fallon area and Dixie valley (Hickman et al., 2000; Hickman et al., 1998 Robertson-Tait et al., 2004; Hickman and Davatzes, 2011; Davatzes and Hickman, 2006; Blake and Davatzes 2011; Blake and Davatzes, 2012). Based on inversion of fault kinematic data, Edwards (2013) interpreted that two discrete stress orientations are preserved at Neal Hot Springs. An older episode of east-west directed extension and a younger episode of southwest-northeast directed sinistral, oblique -normal extension. This interpretation is consistent with the evolution of Cenozoic tectonics in the region (Edwards, 2013). As such we applied a southwest-northeast (060) directed normal faulting stress regime, consistent with the younger extensional episode, to the Neal Hot Springs faults. Under these stress conditions northeast striking steeply dipping fault segments have the highest tendency to dilate and northeast striking 60° dipping fault segments have the highest tendency to slip. Under these stress condition...

Slip and Dilation Tendency Analysis of the Tuscarora Geothermal Area

DOE Data Explorer

Faulds, James E.

2013-12-31

Critically stressed fault segments have a relatively high likelihood of acting as fluid flow conduits (Sibson, 1994). As such, the tendency of a fault segment to slip (slip tendency; Ts; Morris et al., 1996) or to dilate (dilation tendency; Td; Ferrill et al., 1999) provides an indication of which faults or fault segments within a geothermal system are critically stressed and therefore likely to transmit geothermal fluids. The slip tendency of a surface is defined by the ratio of shear stress to normal stress on that surface: Ts = τ / σn (Morris et al., 1996). Dilation tendency is defined by the stress acting normal to a given surface: Td = (σ1-σn) / (σ1-σ3) (Ferrill et al., 1999). Slip and dilation were calculated using 3DStress (Southwest Research Institute). Slip and dilation tendency are both unitless ratios of the resolved stresses applied to the fault plane by ambient stress conditions. Values range from a maximum of 1, a fault plane ideally oriented to slip or dilate under ambient stress conditions to zero, a fault plane with no potential to slip or dilate. Slip and dilation tendency values were calculated for each fault in the focus study areas at, McGinness Hills, Neal Hot Springs, Patua, Salt Wells, San Emidio, and Tuscarora on fault traces. As dip is not well constrained or unknown for many faults mapped in within these we made these calculations using the dip for each fault that would yield the maximum slip tendency or dilation tendency. As such, these results should be viewed as maximum tendency of each fault to slip or dilate. The resulting along-fault and fault-to-fault variation in slip or dilation potential is a proxy for along fault and fault-to-fault variation in fluid flow conduit potential. Stress Magnitudes and directions Stress field variation within each focus area was approximated based on regional published data and the world stress database (Hickman et al., 2000; Hickman et al., 1998 Robertson-Tait et al., 2004; Hickman and Davatzes, 2010; Davatzes and Hickman, 2006; Blake and Davatzes 2011; Blake and Davatzes, 2012; Moeck et al., 2010; Moos and Ronne, 2010 and Reinecker et al., 2005) as well as local stress information if applicable. For faults within these focus systems we applied either a normal faulting stress regime where the vertical stress (sv) is larger than the maximum horizontal stress (shmax) which is larger than the minimum horizontal stress (sv>shmax>shmin) or strike-slip faulting stress regime where the maximum horizontal stress (shmax) is larger than the vertical stress (sv) which is larger than the minimum horizontal stress (shmax >sv>shmin) depending on the general tectonic province of the system. Based on visual inspection of the limited stress magnitude data in the Great Basin we used magnitudes such that shmin/shmax = .527 and shmin/sv= .46, which are consistent with complete and partial stress field determinations from Desert Peak, Coso, the Fallon area and Dixie valley (Hickman et al., 2000; Hickman et al., 1998 Robertson-Tait et al., 2004; Hickman and Davatzes, 2011; Davatzes and Hickman, 2006; Blake and Davatzes 2011; Blake and Davatzes, 2012). Slip and dilation tendency for the Tuscarora geothermal field was calculated based on the faults mapped Tuscarora area (Dering, 2013). The Tuscarora area lies in the Basin and Range Province, as such we applied a normal faulting stress regime to the Tuscarora area faults, with a minimum horizontal stress direction oriented 115, based on inspection of local and regional stress determinations, as explained above. Under these stress conditions north-northeast striking, steeply dipping fault segments have the highest dilation tendency, while north-northeast striking 60° dipping fault segments have the highest tendency to slip. Tuscarora is defined by a left-step in a major north- to-north northeast striking, west-dipping range-bounding normal fault system. Faults within the broad step define an anticlinal accommodation zone...

Experimental investigation of flow and slip transition in nanochannels

NASA Astrophysics Data System (ADS)

Li, Zhigang; Li, Long; Mo, Jingwen

2014-11-01

Flow slip in nanochannels is sought in many applications, such as sea water desalination and molecular separation, because it can enhance fluid transport, which is essential in nanofluidic systems. Previous findings about the slip length for simple fluids at the nanoscale appear to be controversial. Some experiments and simulations showed that the slip length is independent of shear rate, which agrees with the prediction of classic slip theories. However, there is increasing work showing that slip length is shear rate dependent. In this work, we experimentally investigate the Poiseuille flows in nanochannels. It is found that the flow rate undergoes a transition between two linear regimes as the shear rate is varied. The transition indicates that the non-slip boundary condition is valid at low shear rate. When the shear rate is larger than a critical value, slip takes place and the slip length increases linearly with increasing shear rate before approaching a constant value. The results reported in this work can help advance the understanding of flow slip in nanochannels. This work was supported by the Research Grants Council of the Hong Kong Special Administrative Region under Grant Nos. 615710 and 615312. J. Mo was partially supported by the Postgraduate Scholarship through the Energy Program at HKUST.

Axial dispersion, holdup and slip velocity of dispersed phase in a pulsed sieve plate extraction column by radiotracer residence time distribution analysis.

PubMed

Din, Ghiyas Ud; Chughtai, Imran Rafiq; Inayat, Mansoor Hameed; Khan, Iqbal Hussain

2008-12-01

Axial dispersion, holdup and slip velocity of dispersed phase have been investigated for a range of dispersed and continuous phase superficial velocities in a pulsed sieve plate extraction column using radiotracer residence time distribution (RTD) analysis. Axial dispersion model (ADM) was used to simulate the hydrodynamics of the system. It has been observed that increase in dispersed phase superficial velocity results in a decrease in its axial dispersion and increase in its slip velocity while its holdup increases till a maximum asymptotic value is achieved. An increase in superficial velocity of continuous phase increases the axial dispersion and holdup of dispersed phase until a maximum value is obtained, while slip velocity of dispersed phase is found to decrease in the beginning and then it increases with increase in superficial velocity of continuous phase.

Seismic sources in El Salvador. A geological and geodetic contribution

NASA Astrophysics Data System (ADS)

Alonso-Henar, J.; Martínez-Díaz, J. J.; Benito, B.; Alvarez-Gomez, J. A.; Canora, C.; Capote, R.; Staller, A.; Tectónica Activa, Paleosismicidad y. Riesgos Asociados UCM-910368

2013-05-01

El Salvador Fault Zone is a deformation band of 150 km long and 20 km wide within the Salvadorian volcanic arc. This shear band distributes the deformation between main strike-slip faults trending N90°-100°E and around 30 km long, and secondary normal faults trending between N120°E and N170°E. The ESFZ continues westward and is relieved by the Jalpatagua Fault. Eastward ESFZ becomes less clear disappearing at Golfo de Fonseca. The ESFZ deforms and offsets quaternary deposits with a right lateral movement in its main segments. Five segments have been proposed for the whole fault zone, from the Jalpatagua Fault to the Golfo de Fonseca. Paleoseismic studies in the Berlin and San Vicente Segments reveal an important amount of quaternary deformation. In fact, the San Vicente Segment was the source of the February 13, 2001 destructive earthquake. In this work we propose 18 capable seismic sources within El Salvador. The slip rate of each source has been obtained through out the combination of GPS data and paleoseismic data when it has been possible. We also have calculated maximum theoretical intensities produced by the maximum earthquakes related with each fault. We have taken into account several scenarios considering different possible surface rupture lengths up to 50 km and Mw 7.6 in some of the strike slip faults within ESFZ.

Effect of the viscosity of the liquid on the angle of inclination of a wet sandpile*

NASA Astrophysics Data System (ADS)

Samadani, Azadeh; Kudrolli, Arshad

2002-03-01

We study the effect of liquids on the angle of inclination of a wet sandpile in a rotating drum system. In this system, the surface exhibits stick slip motion for slow rotation rates omega, and continuos avalanching above a critical omega. We will focus on the stick-slip regime, where the angle of inclination of the pile oscillates between the maximum angle of stability before an avalanche, and the angle of repose after the avalanche. Both angles are observed to increase and saturate as a function of the volume fraction of the fluid. Furthermore, by changing the viscosity of the fluid using water-glycerol mixtures, we observe that both the maximum angle of stability and the angle of repose increase with the viscosity of the fluid. There are two possible explanations for the increase of the angle of stability of the pile. First, there may be creep motion between the particles giving rise to viscous forces before an avalanche, that are too small to observe visually. The creep motion is also slower than the rate of increase of the surface due to rotation. Second, the average number of liquid bridges between particles may increase with viscosity. We will comment on both possibilities using experimental data and scaling arguments.

InSAR measurements for the 2014 Mw 6.0 Jinggu, Yunnan Earthquake

NASA Astrophysics Data System (ADS)

Chen, Jiajun; Feng, Wanpeng; Sergey, Samsonov; Mahdi, Motagh; Li, Zhenhong; Clarke, Peter

2016-04-01

An earthquake occurred in the southwest of Yunnan, China on 7 October 2014 at 21:49 local time, measured as Mw 6.0 by the United States Geological Survey and Mw 6.1 by the European Alert System. Strong earthquakes are common in this region because of the continental collision between the India and Eurasia plates with a relative convergence rate of 40-50 mm/yr. A detailed study of this earthquake will therefore allow better understanding of regional fault properties. For the first time, Radarsat-2 (RS2) data was employed to investigate co-seismic surface movements of this event. Two ascending RS2 images acquired on 2 October 2014 and 19 November 2014 were used to generate an interferogram, revealing line-of-sight (LOS) displacements with a maximum value of 0.13 m (towards the satellite) in the NW sector. We use PSOKINV to determine fault geometric parameters and slip distribution. First, fault parameters are determined using improved particle swarm optimization. Second, slip distribution over the fault plane is retrieved using an iterative strategy for estimating optimal dip angle and smoothing factors [Feng et al., 2013]. The comparison between the modelled LOS changes and the measured ones shows a good fit, with residuals smaller than 0.02 m. The best-fitting model suggests that the rupture occurred on a left-lateral strike-slip fault with a strike of 323°. The total released moment is equivalent to Mw 6.1 and the main slip zone is confined between depths of 2-8 km. A maximum slip of 1.1 m appears at a depth of 4.3 km, with a rupture length of about 10km. Reference: Feng, W., Z. Li, J. R. Elliott, Y. Fukushima, T. Hoey, A. Singleton, R. Cook, and Z. Xu (2013), The 2011 MW 6.8 Burma earthquake: fault constraints provided by multiple SAR techniques, Geophysical Journal International, doi:10.1093/gji/ggt254.

Regional Slip Tendency Analysis of the Great Basin Region

DOE Data Explorer

Faulds, James E.

2013-09-30

Slip and dilation tendency on the Great Basin fault surfaces (from the USGS Quaternary Fault Database) were calculated using 3DStress (software produced by Southwest Research Institute). Slip and dilation tendency are both unitless ratios of the resolved stresses applied to the fault plane by the measured ambient stress field. - Values range from a maximum of 1 (a fault plane ideally oriented to slip or dilate under ambient stress conditions) to zero (a fault plane with no potential to slip or dilate). - Slip and dilation tendency values were calculated for each fault in the Great Basin. As dip is unknown for many faults in the USGS Quaternary Fault Database, we made these calculations using the dip for each fault that would yield the maximum slip or dilation tendency. As such, these results should be viewed as maximum slip and dilation tendency. - The resulting along‐fault and fault‐to‐fault variation in slip or dilation potential is a proxy for along fault and fault‐to‐fault variation in fluid flow conduit potential. Stress Magnitudes and directions were calculated across the entire Great Basin. Stress field variation within each focus area was approximated based on regional published data and the world stress database (Hickman et al., 2000; Hickman et al., 1998 Robertson‐Tait et al., 2004; Hickman and Davatzes, 2010; Davatzes and Hickman, 2006; Blake and Davatzes 2011; Blake and Davatzes, 2012; Moeck et al., 2010; Moos and Ronne, 2010 and Reinecker et al., 2005). The minimum horizontal stress direction (Shmin) was contoured, and spatial bins with common Shmin directions were calculated. Based on this technique, we subdivided the Great Basin into nine regions (Shmin <070, 070140). Slip and dilation tendency were calculated using 3DStress for the faults within each region using the mean Shmin for the region. Shmin variation throughout Great Basin are shown on Figure 3. For faults within the Great Basin proper, we applied a normal faulting stress regime, where the vertical stress (sv) is larger than the maximum horizontal stress (shmax), which is larger than the minimum horizontal stress (sv>shmax>shmin). Based on visual inspection of the limited stress magnitude data in the Great Basin, we used magnitudes such that shmin/shmax = .527 and shmin/sv= .46. These values are consistent with stress magnitude data at both Dixie Valley (Hickman et al., 2000) and Yucca Mountain (Stock et al., 1985). For faults within the Walker Lane/Eastern California Shear Zone, we applied a strike‐slip faulting stress, where shmax > sv > shmin. Upon visual inspection of limited stress magnitude data from the Walker Lane and Eastern California Shear zone, we chose values such that SHmin/SHmax = .46 and Shmin/Sv= .527 representative of the region. Results: The results of our slip and dilation tendency analysis are shown in Figures 4 (dilation tendency), 5 (slip tendency) and 6 (slip tendency + dilation tendency). Shmin varies from northwest to east‐west trending throughout much of the Great Basin. As such, north‐ to northeast‐striking faults have the highest tendency to slip and to dilate, depending on the local trend of shmin. These results provide a first order filter on faults and fault systems in the Great Basin, affording focusing of local‐scale exploration efforts for blind or hidden geothermal resources.

Slip in the 2015 Mw 7.9 Gorkha and Mw 7.3 Kodari, Nepal, earthquakes revealed by seismic and geodetic data: Delayed slip in the Gorkha and slip deficit between the two earthquakes

NASA Astrophysics Data System (ADS)

Zhang, G.; Hetland, E.; Shan, X.

2017-12-01

We investigate the rupture process of the April 25, 2015 Gorkha, Nepal Mw7.9 earthquake, and its biggest aftershock on May 12, 2015, based on joint inversion of teleseismic body waves, InSAR and GPS measurements. The Gorkha earthquake propagated unilaterally to the southeast along the MFT, with coseismic slip separating into patches up-dip and down-dip of the hypocenter. Slip in the up-dip patch initially surrounded a region on the fault that did not slip. About 15 seconds after being surrounded, this region of no slip then slipped, filling in the slip deficit. The delayed slip accounts for about 20% of the moment release in the Gorkha earthquake. The inferred coseismic slip in the Kodari earthquake is localized to one patch, extending to the south and southeast from the hypocenter, and 20-30 km to the northeast of the main slip patch in the Ghorka earthquake. The maximum coseismic slip in both the Gorkha and Kodari earthquakes is about 4.5 meters.

Slip along the Sultanhanı Fault in Central Anatolia from deformed Pleistocene shorelines of palaeo-lake Konya and implications for seismic hazards in low-strain regions

NASA Astrophysics Data System (ADS)

Melnick, Daniel; Yıldırım, Cengiz; Hillemann, Christian; Garcin, Yannick; Çiner, Attila; Pérez-Gussinyé, Marta; Strecker, Manfred R.

2017-06-01

Central Anatolia is a low-relief, high-elevation region where decadal-scale deformation rates estimated from space geodesy suggest low strain rates within a stiff microplate. However, numerous Quaternary faults have been mapped within this low-strain region and estimating their slip rate and seismic potential is important for hazard assessments in an area of increasing infrastructural development. Here we focus on the Sultanhanı Fault (SF), which constitutes an integral part of the Eskişehir-Cihanbeyli Fault System, and use deformed maximum highstand shorelines of palaeo-lake Konya to estimate tectonic slip rates at millennial scale. Some of these shorelines were previously interpreted as fault scarps, but we provide conclusive evidence for their erosional origin. We found that shoreline-angle elevations estimated from differential GPS profiles record vertical displacements of 10.2 m across the SF. New radiocarbon ages of lacustrine molluscs suggest 22.4 m of relative lake-level fall between 22.1 ± 0.3 and 21.7 ± 0.4 cal. ka BP, constraining the timing of abrupt abandonment of the highstand shoreline. Models of lithospheric rebound associated with regressions of the Tuz Gölü and Konya palaeo-lakes predict only ∼1 m of regional-scale uplift across the Konya Basin. Dislocation models of displaced shorelines suggest fault-slip rates of 1.5 and 1.8 mm yr-1 for planar and listric fault geometries, respectively, providing reasonable results for the latter. We found fault scarps in the Nasuhpınar mudflat that likely represent the most recent ground-breaking rupture of the SF, with an average vertical displacement of 1.2 ± 0.5 m estimated from 54 topographic profiles, equivalent to a M ∼ 6.5-6.9 earthquake based on empirical scaling laws. If such events were characteristic during the ultimate 21 ka, a relatively short recurrence time of ∼800-900 yr would be needed to account for the millennial slip rate. Alternatively, the fault scarp at Nasuhpınar might represent a larger earthquake requiring more frequent smaller events to account for the millennial rate. The relatively fast slip rate of the SF over the past 21 ka is unlikely to have persisted over longer timescales and might reflect spatiotemporal variations in deformation rates within kinematically-linked fault systems within Central Anatolia, or a transient perturbation to the local stress field or fault strength. Such perturbation might have been related to climatically controlled changes in surface and near-surface loads and by interactions among the different tectonic processes that have been proposed to drive the overall slow uplift and associated extension in the Central Anatolian Plateau.

Late Quaternary history of the Owens Valley fault zone, eastern California, and surface rupture associated with the 1872 earthquake

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beanland, S.; Clark, M.M.

1993-04-01

The right-lateral Owens Valley fault zone (OVFZ) in eastern California extends north about 100 km from near the northwest shore of Owens Lake to beyond Big Pine. It passes through Lone Pine near the eastern base of the Alabama Hills and follows the floor of Owens Valley northward to the Poverty Hills, where it steps 3 km to the left and continues northwest across Crater Mountain and through Big Pine. Data from one site suggest an average net slip rate for the OVFZ of 1.5 [+-] 1 mm/yr for the past 300 ky. Several other sites yield an average Holocenemore » net slip rate of 2 [+-] 1 mm/yr. The OVFZ apparently has experienced three major Holocene earthquakes. The minimum average recurrence interval is 5,000 years at the subsidiary Lone Pine fault, whereas it is 3,300 to 5,000 years elsewhere along the OVFZ. The prehistoric earthquakes are not dated, so an average recurrence interval need not apply. However, roughly equal (characteristic) displacement apparently happened during each Holocene earthquake. The Owens Valley fault zone accommodates some of the relative motion (dextral shear) between the North American and Pacific plates along a discrete structure. This shear occurs in the Walker Lane belt of normal and strike-slip faults within the mainly extensional Basin and Range Province. In Owens Valley displacement is partitioned between the OVFZ and the nearby, subparallel, and purely normal range-front faults of the Sierra Nevada. Compared to the OVFZ, these range-front normal faults are very discontinuous and have smaller Holocene slip rates of 0.1 to 0.8 mm/yr, dip slip. Contemporary activity on adjacent faults of such contrasting styles suggests large temporal fluctuations in the relative magnitudes of the maximum and intermediate principal stresses while the extension direction remains consistently east-west.« less

Rushing, distraction, walking on contaminated floors and risk of slipping in limited-service restaurants: a case--crossover study.

PubMed

Verma, Santosh K; Lombardi, David A; Chang, Wen Ruey; Courtney, Theodore K; Huang, Yueng-Hsiang; Brennan, Melanye J; Mittleman, Murray A; Ware, James H; Perry, Melissa J

2011-08-01

This nested case-crossover study examined the association between rushing, distraction and walking on a contaminated floor and the rate of slipping, and whether the effects varied according to weekly hours worked, job tenure and use of slip-resistant shoes. At baseline, workers from 30 limited-service restaurants in the USA reported average work hours, average weekly duration of exposure to each transient risk factor and job tenure at the current location. Use of slip-resistant shoes was determined. During the following 12 weeks, participants reported weekly their slip experience and exposures to the three transient exposures at the time of slipping. The case-crossover design was used to estimate the rate ratios using the Mantel-Haenszel estimator for person-time data. Among 396 participants providing baseline information, 210 reported one or more slips with a total of 989 slips. Rate of slipping was 2.9 times higher when rushing as compared to working at a normal pace (95% CI 2.5 to 3.3). Rate of slipping was also significantly increased by distraction (rate ratio (RR) 1.7, 95% CI 1.5 to 2.0) and walking on a contaminated floor (RR 14.6, 95% CI 12.6 to 17.0). Use of slip-resistant shoes decreased the effects of rushing and walking on a contaminated floor. Rate ratios for all three transient factors decreased monotonically as job tenure increased. The results suggest the importance of these transient risk factors, particularly floor contamination, on rate of slipping in limited-service restaurant workers. Stable characteristics, such as slip-resistant shoes, reduced the effects of transient exposures.

Crustal Deformation and the Seismic Cycle across the Kodiak Islands, Alaska

NASA Technical Reports Server (NTRS)

Sauber, Jeanne; Carver, G.; Cohen, Steven C.; King, Robert

2004-01-01

The Kodiak Islands are located approximately 130 to 250 km from the Alaska-Aleutian Trench where the Pacific plate is underthrusting the North American plate at a rate of about 57 mm/yr. The southern extent of the 1964 Prince William Sound (${M-w}$ = 9.2) earthquake rupture occurred offshore and beneath the eastern portion of the Kodiak Islands. Here we report GPS results (1993-2001) from northern Kodiak Island that span the transition between the 1964 uplift region along the eastern coast and the region of coseismic subsidence further inland. The horizontal velocity vectors range from 22.9 $\\pm$ 2.2 mm/yr at N26.3$\\deg$W $\\pm$ 2.5$\\deg$, about 150 km from the trench, to 5.9 $\\pm$ 1.3 mm/yr at N65.9$\\deg$W $\\pm$ 6.6$\\deg$, about 190 km from the trench. Near the northeastern coast of Kodiak the velocity vector above the shallow, locked main thrust zone is between the orientation of PCFC-NOAM plate motion (N22$/deg$W) and the trench-normal (N3O$\\deg$W). Further west, our geodetic results suggest the accumulation of shear strain that will be released eventually as left-lateral motion on upper plate faults such as the Kodiak Island fault. These results are consistent with the hypothesis that the difference between the Pacific-North American plate motion and the orientation of the down going slab would lead to 4-8 mm/yr of left-lateral slip. Short-term geodetic uplift rates range from 2 - 14 mm/yr, with the maximum uplift located near the axis of maximum subsidence during the 1964 earthquake. We evaluated alternate interseismic models for Kodiak to test the importance of various mechanisms responsible for crustal deformation rates. These models are based on the plate interface slip history inferred from earlier modeling of coseismic and post-seismic geodetic results. The horizontal (trench perpendicular) and vertical deformation rates across Kodiak are consistent with a model that includes the viscoelastic response to : (1) a downgoing Pacific plate interface that is locked at shallow depths,(2) coseismic slip in the 1964 and (3) interseismic creep below the seismogenic zone. The change in orientation of the horizontal velocity vector occurs down-dip from the locked main thrust zone. In southern Kodiak, the coseismic slip in the 1964 earthquake was smaller than in the northern Kodiak region; yet, the horizontal, interseismic velocities as a function of distance from the trench are comparable to those in northern Kodiak. Based on the earthquake history prior to, and following the 1964 earthquake, we hypothesize that the plate interface in southern Kodiak slips in more frequent large earthquakes than in northern Kodiak.

Slip-accumulation patterns and earthquake recurrences along the Talas-Fergana Fault - Contributions of high-resolution geomorphic offsets.

NASA Astrophysics Data System (ADS)

Rizza, M.; Dubois, C.; Fleury, J.; Abdrakhmatov, K.; Pousse, L.; Baikulov, S.; Vezinet, A.

2017-12-01

In the western Tien-Shan Range, the largest intracontinental strike-slip fault is the Karatau-Talas Fergana Fault system. This dextral fault system is subdivided into two main segments: the Karatau fault to the north and the Talas-Fergana fault (TFF) to the south. Kinematics and rates of deformation for the TFF during the Quaternary period are still debated and are poorly constrained. Only a few paleoseismological investigations are availabe along the TFF (Burtman et al., 1996; Korjenkov et al., 2010) and no systematic quantifications of the dextral displacements along the TFF has been undertaken. As such, the appraisal of the TFF behavior demands new tectonic information. In this study, we present the first detailed analysis of the morphology and the segmentation of the TFF and an offset inventory of morphological markers along the TFF. To discuss temporal and spatial recurrence patterns of slip accumulated over multiple seismic events, our study focused on a 60 km-long section of the TFF (Chatkal segment). Using tri-stereo Pleiades satellite images, high-resolution DEMs (1*1 m pixel size) have been generated in order to (i) analyze the fine-scale fault geometry and (ii) thoroughly measure geomorphic offsets. Photogrammetry data obtained from our drone survey on high interest sites, provide higher-resolution DEMs of 0.5 * 0.5 m pixel size.Our remote sensing mapping allows an unprecedented subdivision - into five distinct segments - of the study area. About 215 geomorphic markers have been measured and offsets range from 4.5m to 180 m. More than 80% of these offsets are smaller than 60 m, suggesting landscape reset during glacial maximum. Calculations of Cumulative Offset Probability Density (COPD) for the whole 60 km-long section as well as for each segments support distinct behavior from a segment to another and thus variability in slip-accumulation patterns. Our data argue for uniform slip model behavior along this section of the TFF. Moreover, we excavated a trench and found evidence for two earthquakes. Analysis of radiocarbon and OSL samples collected in the excavation will provide constraints on the timing of those two events. We also collected some surficial samples for cosmogenic dating to determine the geological slip-rate at two sites and to discuss some spatial slip-rate variations along the TFF.

Triggered reverse fault and earthquake due to crustal unloading, northwest Transverse Ranges, California.

USGS Publications Warehouse

Yerkes, R.F.; Ellsworth, W.L.; Tinsley, J.C.

1983-01-01

A reverse-right-oblique surface rupture, associated with a ML 2.5 earthquake, formed in a diatomite quarry near Lompoc, California, in the northwesternmost Transverse Ranges on April 7, 1981. The 575-m-long narrow zone of ruptures formed in clay interbeds in diatomite and diatomaceous shale of the Neogene Monterey Formation. The ruptures parallel bedding, dip 39o-59oS, and trend about N84oE on the north limb of an open symmetrical syncline. Maximum net slip was 25 cm; maximum reverse dip slip was 23 cm, maximum right-lateral strike slip was about 9 cm, and average net slip was about 12 cm. The seismic moment of the earthquake is estimated at 1 to 2 X 1018 dyne/cm and the static stress drop at about 3 bar. The removal of an average of about 44 m of diatomite resulted in an average load reduction of about 5 bar, which decreased the normal stress by about 3.5 bar and increased the shear stress on the tilted bedding plane by about 2 bar. The April 7, 1981, event was a very shallow bedding-plane rupture, apparently triggered by crustal unloading. -Authors

Slow slip and self-similar asymptotics of rate-strengthening faults

NASA Astrophysics Data System (ADS)

Viesca, R. C.; Dublanchet, P.

2016-12-01

We examine how slow slip progresses on rate-strengthening faults. We consider that the source of rate-strengthening may be a linear or non-linear (power-law) viscous fault rheology, a logarithmic rate-dependence, or a Dieterich-Ruina dependence on slip rate and its history. We show the existence of self-similar asymptotic solutions for slip rate of the form V = t^alpha f(x/t^beta). The exponent beta is determined by the nature of the elastic interaction (for slip between elastic half-spaces in contact, beta = 1; and for layer sliding above a substrate, beta = 1/2). The similarity exponent alpha is determined by the type of initial or boundary conditions. Such conditions may be, for example, an imposed (i) boundary slip rate or (ii) a sudden change in stress on the fault. We consider in-plane or anti-plane slip for examples (i) and (ii) and present the asymptotic solutions thereof, which may be found numerically or in closed form. The self-similar behavior of scenario (i) is, for a step increase in stress, that of an initially elevated slip rate decaying in time while spreading in space; and of scenario (ii) is that an elevated slip rate propagating along the fault. Under scenario (i) we show that the disparate fault rheologies share a common closed-form similarity solution for the decay of slip rate following the initial stress change. For comparison, we compute numerical solutions to the evolution equation for slip rate (and state, when applicable) and find precise agreement with the above analysis. We illustrate how the above solutions provide robust, low-parameter models to test whether there is a frictional basis for spatio-temporal observations indicating the accumulation of post-seismic slip or the occurrence of slow slip event. Such observations include those derived from (a) geodetic observations [e.g., Hsu et al., Science 2006], or migration of (b) low-frequency earthquakes and tremor [e.g., Obara and Hirose, Tectonophys. 2006], and of (c) micro-seismicity [e.g., Bourouis and Bernard, Geophys. J. Int., 2007].

A prospective study of floor surface, shoes, floor cleaning and slipping in US limited-service restaurant workers.

PubMed

Verma, Santosh K; Chang, Wen Ruey; Courtney, Theodore K; Lombardi, David A; Huang, Yueng-Hsiang; Brennan, Melanye J; Mittleman, Murray A; Ware, James H; Perry, Melissa J

2011-04-01

Slips and falls are a leading cause of injury at work. Few studies, however, have systematically examined risk factors of slipping outside the laboratory environment. This study examined the association between floor surface characteristics, slip-resistant shoes, floor cleaning frequency and the risk of slipping in limited-service restaurant workers. 475 workers from 36 limited-service restaurants from three major chains in six states in the USA were recruited to participate in a prospective cohort study of workplace slipping. Kitchen floor surface roughness and coefficient of friction (COF) were measured in eight working areas and then averaged within each restaurant. The use of slip-resistant shoes was determined by examining the participant's shoes and noting the presence of a 'slip-resistant' marking on the sole. Restaurant managers reported the frequency of daily kitchen floor cleaning. Participants reported their slip experience and work hours weekly for up to 12 weeks. The survey materials were made available in three languages: English, Spanish and Portuguese. The associations between rate of slipping and risk factors were assessed using a multivariable negative binomial generalised estimating equation model. The mean of individual slipping rate varied among the restaurants from 0.02 to 2.49 slips per 40 work hours. After adjusting for age, gender, BMI, education, primary language, job tenure and restaurant chain, the use of slip-resistant shoes was associated with a 54% reduction in the reported rate of slipping (95% CI 37% to 64%), and the rate of slipping decreased by 21% (95% CI 5% to 34%) for each 0.1 increase in the mean kitchen COF. Increasing floor cleaning frequency was significantly associated with a decreasing rate of slipping when considered in isolation but not after statistical adjustment for other factors. These results provide support for the use of slip-resistant shoes and measures to increase COF as preventive interventions to reduce slips, falls and injuries.

Strain accumulation and rotation in the Eastern California Shear Zone

USGS Publications Warehouse

Savage, J.C.; Gan, Weijun; Svarc, J.L.

2001-01-01

Although the Eastern California Shear Zone (ECSZ) (strike ???N25??W) does not quite coincide with a small circle drawn about the Pacific-North America pole of rotation, trilateration and GPS measurements demonstrate that the motion within the zone corresponds to right-lateral simple shear across a vertical plane (strike N33??W??5??) roughly parallel to the tangent to that local small circle (strike ???N40??W). If the simple shear is released by slip on faults subparallel to the shear zone, the accumulated rotation is also released, leaving no secular rotation. South of the Garlock fault the principal faults (e.g., Calico-Blackwater fault) strike ???N40??W, close enough to the strike of the vertical plane across which maximum right-lateral shear accumulates to almost wholly accommodate that accumulation of both strain and rotation by right-lateral slip. North of the Garlock fault dip slip as well as strike slip on the principal faults (strike ???N20??W) is required to accommodate the simple shear accumulation. In both cases the accumulated rotation is released with the shear strain. The Garlock fault, which transects the ECSZ, is not offset by north-northwest striking faults nor, despite geological evidence for long-term left-lateral slip, does it appear at the present time to be accumulating left-lateral simple shear strain across the fault due to slip at depth. Rather the motion is explained by right-lateral simple shear across the orthogonal ECSZ. Left-lateral slip on the Garlock fault will release the shear strain accumulating there but would augment the accumulating rotation, resulting in a secular clockwise rotation rate ???80 nrad yr-1 (4.6?? Myr-1).

Surface faulting and paleoseismic history of the 1932 Cedar Mountain earthquake area, west-central Nevada, and implications for modern tectonics of the Walker Lane

USGS Publications Warehouse

Bell, J.W.; DePolo, C.M.; Ramelli, A.R.; Sarna-Wojcicki, A. M.; Meyer, C.E.

1999-01-01

The 1932 Cedar Mountain earthquake (Ms 7.2) was one of the largest historical events in the Walker Lane region of western Nevada, and it produced a complicated strike-slip rupture pattern on multiple Quaternary faults distributed through three valleys. Primary, right-lateral surface ruptures occurred on north-striking faults in Monte Cristo Valley; small-scale lateral and normal offsets occurred in Stewart Valley; and secondary, normal faulting occurred on north-northeast-striking faults in the Gabbs Valley epicentral region. A reexamination of the surface ruptures provides new displacement and fault-zone data: maximum cumulative offset is estimated to be 2.7 m, and newly recognized faults extend the maximum width and end-to-end length of the rupture zone to 17 and 75 km, respectively. A detailed Quaternary allostratigraphic chronology based on regional alluvialgeomorphic relationships, tephrochronology, and radiocarbon dating provides a framework for interpreting the paleoseismic history of the fault zone. A late Wisconsinan alluvial-fan and piedmont unit containing a 32-36 ka tephra layer is a key stratigraphic datum for paleoseismic measurements. Exploratory trenching and radiocarbon dating of tectonic stratigraphy provide the first estimates for timing of late Quaternary faulting along the Cedar Mountain fault zone. Three trenches display evidence for six faulting events, including that in 1932, during the past 32-36 ka. Radiocarbon dating of organic soils interstratified with tectonically ponded silts establishes best-fit ages of the pre-1932 events at 4, 5,12,15, and 18 ka, each with ??2 ka uncertainties. On the basis of an estimated cumulative net slip of 6-12 m for the six faulting events, minimum and maximum late Quaternary slip rates are 0.2 and 0.7 mm/yr, respectively, and the preferred rate is 0.4-0.5 mm/yr. The average recurrence (interseismic) interval is 3600 yr. The relatively uniform thickness of the ponded deposits suggests that similar-size, characteristic rupture events may characterize late Quaternary slip on the zone. A comparison of event timing with the average late Quaternary recurrence interval indicates that slip has been largely regular (periodic) rather than temporally clustered. To account for the spatial separation of the primary surface faulting in Monte Cristo Valley from the epicenter and for a factor-of-two-to-three disparity between the instrumentally and geologically determined seismic moments associated with the earthquake, we hypothesize two alternative tectonic models containing undetected subevents. Either model would adequately account for the observed faulting on the basis of wrench-fault kinematics that may be associated with the Walker Lane. The 1932 Cedar Mountain earthquake is considered an important modern analogue for seismotectonic modeling and estimating seismic hazard in the Walker Lane region. In contrast to most other historical events in the Basin and Range province, the 1932 event did not occur along a major range-bounding fault, and no single, throughgoing basement structure can account for the observed rupture pattern. The 1932 faulting supports the concept that major earthquakes in the Basin and Range province can exhibit complicated distributive rupture patterns and that slip rate may not be a reliable criterion for modeling seismic hazard.

Variable rates of late Quaternary strike slip on the San Jacinto fault zone, southern California.

USGS Publications Warehouse

Sharp, R.V.

1981-01-01

3 strike slip displacements of strata with known approximate ages have been measured at 2 locations on the San Jacinto fault zone. Minimum horizontal offset between 5.7 and 8.6km in no more than 0.73Myr NE of Anza indicates 8-12 mm/yr average slip rate since late Pleistocene time. Horizontal slip of 1.7m has been calculated for the youngest sediment of Lake Cahuilla since its deposition 271- 510 yr BP. The corresponding slip rate is 2.8-5.0 mm/yr. Right lateral offset of 10.9m measured on a buried stream channel older than 5060 yr BP but younger than 6820 yr BP yields average slip rates for the intermediate time periods, 400 to 6000 yr BP of 1-2 mm/yr. The rates of slip suggest a relatively quiescent period from about 4000 BC to about 1600 AD.-from Author

Late Pleistocene, Holocene, and decadal constancy of slip-rate of the Doruneh strike-slip fault, Iran.

NASA Astrophysics Data System (ADS)

Walker, R. T.; Fattahi, M.; Mousavi, Z.; Pathier, E.; Sloan, R. A.; Talebian, M.; Thomas, A. L.; Walpersdorf, A.

2014-12-01

The Doruneh left-lateral strike-slip fault of NE Iran has a prominent expression in the landscape, showing that the fault is active in the late Quaternary. Existing estimates of its slip-rate vary, however, which has led to suggestions that it may exhibit temporal changes in activity. Using high-resolution optical satellite imagery we make reconstructions of displacement across four alluvial fans that cross the Doruneh fault, and determine the ages of these fans using luminescence dating, combined with U-series dating of pedogenic carbonates in one case. The four fans, which vary in age from 10-100 kyr, yield estimates of slip rate of ~2-3 mm/yr. We compare the average slip-rate measurements to the rate of accumulation of strain across the Doruneh fault using GPS and InSAR measurements, and find that the slip-rate is likely to have remained constant - within the uncertainty of our measurements - over the last ~100 ka. The slip-rate that we measure is consistent with the E-W left-lateral Doruneh fault accommodating N-S right-lateral faulting by 'bookshelf' faulting, with clockwise rotation about a vertical axis, in a similar manner to the Eastern California Shear Zone.

Millennial strain partitioning and fault interaction revealed by 36Cl cosmogenic nuclide datasets from Abruzzo, Central Italy

NASA Astrophysics Data System (ADS)

Gregory, L. C.; Phillips, R. J.; Roberts, G.; Cowie, P. A.; Shanks, R. P.; McCaffrey, K. J. W.; Wedmore, L. N. J.; Zijerveld, L.

2015-12-01

In zones of distributed continental faulting, it is critical to understand how slip is partitioned onto brittle structures over both long-term millennial time scales and shorter-term individual earthquake cycles. The comparison of slip distributions on different timescales is challenging due to earthquake repeat-times being longer or similar to historical earthquake records, and a paucity of data on fault activity covering millennial to Quaternary scales in detail. Cosmogenic isotope analyses from bedrock fault scarps have the potential to bridge the gap, as these datasets track the exposure of fault planes due to earthquakes with better-than-millennial resolution. In this presentation, we will use an extensive 36Cl dataset to characterise late Holocene activity across a complicated network of normal faults in Abruzzo, Italy, comparing the most recent fault behaviour with the historical earthquake record in the region. Extensional faulting in Abruzzo has produced scarps of exposed bedrock limestone fault planes that have been preserved since the last glacial maximum (LGM). 36Cl accumulates in bedrock fault scarps as the plane is progressively exhumed by earthquakes and thus the concentration of 36Cl measured up the fault plane reflects the rate and patterns of slip. In this presentation, we will focus on the most recent record, revealed at the base of the fault. Utilising new Bayesian modelling techniques on new and previously collected data, we compare evidence for this most recent period of slip (over the last several thousands of years) across 5-6 fault zones located across strike from each other. Each sampling site is carefully characterised using LiDAR and GPR. We demonstrate that the rate of slip on individual fault strands varies significantly, between having periods of accelerated slip to relative quiescence. Where data is compared between across-strike fault zones and with the historical catalogue, it appears that slip is partitioned such that one fault zone takes up a significant portion of strain across the region for hundreds to thousands of years.

46 CFR 56.30-40 - Flexible pipe couplings of the compression or slip-on type.

Code of Federal Regulations, 2011 CFR

2011-10-01

... or slip-on type must not be used as expansion joints. To ensure that the maximum axial displacement... couplings must not be used in cargo holds or in any other space where leakage, undetected flooding, or...

46 CFR 56.30-40 - Flexible pipe couplings of the compression or slip-on type.

Code of Federal Regulations, 2012 CFR

2012-10-01

... or slip-on type must not be used as expansion joints. To ensure that the maximum axial displacement... couplings must not be used in cargo holds or in any other space where leakage, undetected flooding, or...

46 CFR 56.30-40 - Flexible pipe couplings of the compression or slip-on type.

Code of Federal Regulations, 2014 CFR

2014-10-01

... or slip-on type must not be used as expansion joints. To ensure that the maximum axial displacement... couplings must not be used in cargo holds or in any other space where leakage, undetected flooding, or...

46 CFR 56.30-40 - Flexible pipe couplings of the compression or slip-on type.

Code of Federal Regulations, 2013 CFR

2013-10-01

... or slip-on type must not be used as expansion joints. To ensure that the maximum axial displacement... couplings must not be used in cargo holds or in any other space where leakage, undetected flooding, or...

46 CFR 56.30-40 - Flexible pipe couplings of the compression or slip-on type.

Code of Federal Regulations, 2010 CFR

2010-10-01

... or slip-on type must not be used as expansion joints. To ensure that the maximum axial displacement... couplings must not be used in cargo holds or in any other space where leakage, undetected flooding, or...

Slip and Dilation Tendency Analysis of the Patua Geothermal Area

DOE Data Explorer

Faulds, James E.

2013-12-31

Critically stressed fault segments have a relatively high likelihood of acting as fluid flow conduits (Sibson, 1994). As such, the tendency of a fault segment to slip (slip tendency; Ts; Morris et al., 1996) or to dilate (dilation tendency; Td; Ferrill et al., 1999) provides an indication of which faults or fault segments within a geothermal system are critically stressed and therefore likely to transmit geothermal fluids. The slip tendency of a surface is defined by the ratio of shear stress to normal stress on that surface: Ts = τ / σn (Morris et al., 1996). Dilation tendency is defined by the stress acting normal to a given surface: Td = (σ1-σn) / (σ1-σ3) (Ferrill et al., 1999). Slip and dilation were calculated using 3DStress (Southwest Research Institute). Slip and dilation tendency are both unitless ratios of the resolved stresses applied to the fault plane by ambient stress conditions. Values range from a maximum of 1, a fault plane ideally oriented to slip or dilate under ambient stress conditions to zero, a fault plane with no potential to slip or dilate. Slip and dilation tendency values were calculated for each fault in the focus study areas at, McGinness Hills, Neal Hot Springs, Patua, Salt Wells, San Emidio, and Tuscarora on fault traces. As dip is not well constrained or unknown for many faults mapped in within these we made these calculations using the dip for each fault that would yield the maximum slip tendency or dilation tendency. As such, these results should be viewed as maximum tendency of each fault to slip or dilate. The resulting along-fault and fault-to-fault variation in slip or dilation potential is a proxy for along fault and fault-to-fault variation in fluid flow conduit potential. Stress Magnitudes and directions Stress field variation within each focus area was approximated based on regional published data and the world stress database (Hickman et al., 2000; Hickman et al., 1998 Robertson-Tait et al., 2004; Hickman and Davatzes, 2010; Davatzes and Hickman, 2006; Blake and Davatzes 2011; Blake and Davatzes, 2012; Moeck et al., 2010; Moos and Ronne, 2010 and Reinecker et al., 2005) as well as local stress information if applicable. For faults within these focus systems we applied either a normal faulting stress regime where the vertical stress (sv) is larger than the maximum horizontal stress (shmax) which is larger than the minimum horizontal stress (sv>shmax>shmin) or strike-slip faulting stress regime where the maximum horizontal stress (shmax) is larger than the vertical stress (sv) which is larger than the minimum horizontal stress (shmax >sv>shmin) depending on the general tectonic province of the system. Based on visual inspection of the limited stress magnitude data in the Great Basin we used magnitudes such that shmin/shmax = .527 and shmin/sv= .46, which are consistent with complete and partial stress field determinations from Desert Peak, Coso, the Fallon area and Dixie valley (Hickman et al., 2000; Hickman et al., 1998 Robertson-Tait et al., 2004; Hickman and Davatzes, 2011; Davatzes and Hickman, 2006; Blake and Davatzes 2011; Blake and Davatzes, 2012). Slip and dilation tendency analysis for the Patua geothermal system was calculated based on faults mapped in the Hazen Quadrangle (Faulds et al., 2011). Patua lies near the margin between the Basin and Range province, which is characterized by west-northwest directed extension and the Walker Lane province, characterized by west-northwest directed dextral shear. As such, the Patua area likely has been affected by tectonic stress associated with either or both of stress regimes over geologic time. In order to characterize this stress variation we calculated slip tendency at Patua for both normal faulting and strike slip faulting stress regimes. Based on examination of regional and local stress data (as explained above) we applied at shmin direction of 105 to Patua. Whether the vertical stress (sv) magnitude is larger than ...

Slip and Dilation Tendency Anlysis of McGinness Hills Geothermal Area

DOE Data Explorer

Faulds, James E.

2013-12-31

Slip and Dilation Tendency in focus areas Critically stressed fault segments have a relatively high likelihood of acting as fluid flow conduits (Sibson, 1994). As such, the tendency of a fault segment to slip (slip tendency; Ts; Morris et al., 1996) or to dilate (dilation tendency; Td; Ferrill et al., 1999) provides an indication of which faults or fault segments within a geothermal system are critically stressed and therefore likely to transmit geothermal fluids. The slip tendency of a surface is defined by the ratio of shear stress to normal stress on that surface: Ts = τ / σn (Morris et al., 1996). Dilation tendency is defined by the stress acting normal to a given surface: Td = (σ1-σn) / (σ1-σ3) (Ferrill et al., 1999). Slip and dilation were calculated using 3DStress (Southwest Research Institute). Slip and dilation tendency are both unitless ratios of the resolved stresses applied to the fault plane by ambient stress conditions. Values range from a maximum of 1, a fault plane ideally oriented to slip or dilate under ambient stress conditions to zero, a fault plane with no potential to slip or dilate. Slip and dilation tendency values were calculated for each fault in the focus study areas at, McGinness Hills, Neal Hot Springs, Patua, Salt Wells, San Emidio, and Tuscarora on fault traces. As dip is not well constrained or unknown for many faults mapped in within these we made these calculations using the dip for each fault that would yield the maximum slip tendency or dilation tendency. As such, these results should be viewed as maximum tendency of each fault to slip or dilate. The resulting along-fault and fault-to-fault variation in slip or dilation potential is a proxy for along fault and fault-to-fault variation in fluid flow conduit potential. Stress Magnitudes and directions Stress field variation within each focus area was approximated based on regional published data and the world stress database (Hickman et al., 2000; Hickman et al., 1998 Robertson-Tait et al., 2004; Hickman and Davatzes, 2010; Davatzes and Hickman, 2006; Blake and Davatzes 2011; Blake and Davatzes, 2012; Moeck et al., 2010; Moos and Ronne, 2010 and Reinecker et al., 2005) as well as local stress information if applicable. For faults within these focus systems we applied either a normal faulting stress regime where the vertical stress (sv) is larger than the maximum horizontal stress (shmax) which is larger than the minimum horizontal stress (sv>shmax>shmin) or strike-slip faulting stress regime where the maximum horizontal stress (shmax) is larger than the vertical stress (sv) which is larger than the minimum horizontal stress (shmax >sv>shmin) depending on the general tectonic province of the system. Based on visual inspection of the limited stress magnitude data in the Great Basin we used magnitudes such that shmin/shmax = .527 and shmin/sv= .46, which are consistent with complete and partial stress field determinations from Desert Peak, Coso, the Fallon area and Dixie valley (Hickman et al., 2000; Hickman et al., 1998 Robertson-Tait et al., 2004; Hickman and Davatzes, 2011; Davatzes and Hickman, 2006; Blake and Davatzes 2011; Blake and Davatzes, 2012). Slip and dilation tendency for the McGinness Hills geothermal field was calculated based on the faults mapped McGinness Hills area (Siler 2012, unpublished). The McGinness Hills area lies in the Basin and Range Province, as such we applied a normal faulting stress regime to the McGinness area faults, with a minimum horizontal stress direction oriented 115, based on inspection of local and regional stress determinations, as explained above. Under these stress conditions north-northeast striking, steeply dipping fault segments have the highest dilation tendency, while north-northeast striking 60° dipping fault segments have the highest tendency to slip. The McGinness Hills geothermal system is characterized by a left-step in a north-northeast striking west-dipping fault system wit...

Slip rates and spatially variable creep on faults of the northern San Andreas system inferred through Bayesian inversion of Global Positioning System data

USGS Publications Warehouse

Murray, Jessica R.; Minson, Sarah E.; Svarc, Jerry L.

2014-01-01

Fault creep, depending on its rate and spatial extent, is thought to reduce earthquake hazard by releasing tectonic strain aseismically. We use Bayesian inversion and a newly expanded GPS data set to infer the deep slip rates below assigned locking depths on the San Andreas, Maacama, and Bartlett Springs Faults of Northern California and, for the latter two, the spatially variable interseismic creep rate above the locking depth. We estimate deep slip rates of 21.5 ± 0.5, 13.1 ± 0.8, and 7.5 ± 0.7 mm/yr below 16 km, 9 km, and 13 km on the San Andreas, Maacama, and Bartlett Springs Faults, respectively. We infer that on average the Bartlett Springs fault creeps from the Earth's surface to 13 km depth, and below 5 km the creep rate approaches the deep slip rate. This implies that microseismicity may extend below the locking depth; however, we cannot rule out the presence of locked patches in the seismogenic zone that could generate moderate earthquakes. Our estimated Maacama creep rate, while comparable to the inferred deep slip rate at the Earth's surface, decreases with depth, implying a slip deficit exists. The Maacama deep slip rate estimate, 13.1 mm/yr, exceeds long-term geologic slip rate estimates, perhaps due to distributed off-fault strain or the presence of multiple active fault strands. While our creep rate estimates are relatively insensitive to choice of model locking depth, insufficient independent information regarding locking depths is a source of epistemic uncertainty that impacts deep slip rate estimates.

The 2013, Mw 7.7 Balochistan earthquake, energetic strike-slip reactivation of a thrust fault

NASA Astrophysics Data System (ADS)

Avouac, Jean-Philippe; Ayoub, Francois; Wei, Shengji; Ampuero, Jean-Paul; Meng, Lingsen; Leprince, Sebastien; Jolivet, Romain; Duputel, Zacharie; Helmberger, Don

2014-04-01

We analyse the Mw 7.7 Balochistan earthquake of 09/24/2013 based on ground surface deformation measured from sub-pixel correlation of Landsat-8 images, combined with back-projection and finite source modeling of teleseismic waveforms. The earthquake nucleated south of the Chaman strike-slip fault and propagated southwestward along the Hoshab fault at the front of the Kech Band. The rupture was mostly unilateral, propagated at 3 km/s on average and produced a 200 km surface fault trace with purely strike-slip displacement peaking to 10 m and averaging around 6 m. The finite source model shows that slip was maximum near the surface. Although the Hoshab fault is dipping by 45° to the North, in accordance with its origin as a thrust fault within the Makran accretionary prism, slip was nearly purely strike-slip during that earthquake. Large seismic slip on such a non-optimally oriented fault was enhanced possibly due to the influence of the free surface on dynamic stresses or to particular properties of the fault zone allowing for strong dynamic weakening. Strike-slip faulting on thrust fault within the eastern Makran is interpreted as due to eastward extrusion of the accretionary prism as it bulges out over the Indian plate. Portions of the Makran megathrust, some thrust faults in the Kirthar range and strike-slip faults within the Chaman fault system have been brought closer to failure by this earthquake. Aftershocks cluster within the Chaman fault system north of the epicenter, opposite to the direction of rupture propagation. By contrast, few aftershocks were detected in the area of maximum moment release. In this example, aftershocks cannot be used to infer earthquake characteristics.

New investigations of the October 1999 Hector Mine Earthquake surface rupture

NASA Astrophysics Data System (ADS)

Sousa, F.; Harvey, J. C.; Hudnut, K. W.; Akciz, S. O.; Stock, J. M.

2013-12-01

We report on new field and computer based investigation of the surface rupture of the October 16, 1999 Hector Mine Earthquake. In cooperation with the United States Marine Corps Air Ground Combat Center Twentynine Palms (MCAGCC), our team was allowed ground and aerial access to the extent of the surface rupture for limited times during October - December 2012. As far as we know, this was the first scientific access granted to the entire surface rupture since the immediate aftermath of the earthquake, and the first scientific access of any kind to some parts of the maximum slip zone since before the event. This locale is an excellent natural laboratory for detailed study of a major earthquake surface rupture because: 1) complete circumscription within the boundaries of MCAGCC severely limit both past and future human disruption of the rupture, particularly in the mountainous maximum slip zone; 2) groundbreaking aerial LiDAR survey carried out six months after the earthquake was followed up by a higher density, wider swath LiDAR survey in May 2012, making the temporal evolution of this rupture perhaps the most completely physically documented of any major rupture; and 3) field investigation immediately following the event was followed up by computer based offset measurements using the April 2000 LiDAR dataset, providing a database of published offset measurements. Due to time constraints imposed by MCAGGC we focused our new research effort along the ~8 km long maximum slip zone of the rupture, roughly corresponding to the zone of >4 m dextral offset. Our investigation includes 1) walking this entire section of the fault and making >30 measurements of dextral slip while photo documenting the current state of the rupture; 2) creating a difference raster for the entire 8 km maximum slip zone from exactly congruent DEM's made from the 2000 and 2012 LiDAR data sets; 3) documenting the fault traces with a Trimble GeoXH high precision handheld GPS unit (+/- 10 cm); 4) carrying out field checks of a small number of computer-based offset measurements made using the 2000 LiDAR dataset; and 5) high-resolution low-altitude (<100 m AGL) photography of the maximum slip zone during a helicopter overflight. To date, important results include 1) identification of two new maximum slip locations where features are offset 7.9 m +/- 0.5 m and 6.7 m +/- 0.5 m; 2) a database of >30 offset measurements (georeferenced and photo documented) made by our team on the ground; 3) clear changes in fracture visibility in the field, with some fractures more visible, and others no longer visible, compared to the 1999-2000 studies; and 4) examples of a few field checks that both strongly agree and disagree with computer based LiDAR offset measurements.

Slow slip rate and excitation efficiency of deep low-frequency tremors beneath southwest Japan

NASA Astrophysics Data System (ADS)

Daiku, Kumiko; Hiramatsu, Yoshihiro; Matsuzawa, Takanori; Mizukami, Tomoyuki

2018-01-01

We estimated the long-term average slip rate on the plate interface across the Nankai subduction zone during 2002-2013 using deep low-frequency tremors as a proxy for short-term slow slip events based on empirical relations between the seismic moment of short-term slow slip events and tremor activities. The slip rate in each region is likely to compensate for differences between the convergence rate and the slip deficit rate of the subducting Philippine Sea plate estimated geodetically, although the uncertainty is large. This implies that the strain because of the subduction of the plate is partially stored as the slip deficit and partially released by slow slip events during the interseismic period. The excitation efficiency of the tremors for the slow slip events differs among regions: it is high in the northern Kii region. Some events in the western Shikoku region show a somewhat large value. Antigorite serpentinite of two types exists in the mantle wedge beneath southwest Japan. Slips with more effective excitation of tremors presumably occur in high-temperature conditions in the antigorite + olivine stability field. Other slip events with low excitation efficiency are distributed in the antigorite + brucite stability field. Considering the formation reactions of these minerals and their characteristic structures, events with high excitation efficiency can be correlated with a high pore fluid pressure condition. This result suggests that variation in pore fluid pressure on the plate interface affects the magnitude of tremors excited by slow slip events.

Shear-strain energy rate distribution caused by the interplate locking along the Nankai Trough, southwest Japan: An integration analysis using stress tensor inversion and slip deficit inversion

NASA Astrophysics Data System (ADS)

Saito, T.; Noda, A.; Yoshida, K.; Tanaka, S.

2017-12-01

In the Nankai Trough, southwest Japan, the Philippine Sea Plate descends beneath the Eurasian plate. The locking, or the slip deficit, on the plate interface causes stress fluctuation in the inland area. The interplate locking does not always result in stress accumulation but also causes stress release. The stress increase/decrease is not determined only from the stress fluctuation but also depends on the background stress, in particular, its orientation. This study proposes a method to estimate the shear-strain energy increase/decrease distribution caused by the interplate locking. We at first investigated the background stress field in and around the Nankai Trough. The spatial distribution of the principal stress orientations and the stress ratio were estimated by analysis of 130,000 focal mechanisms of small earthquakes (e.g., Yoshida et al. 2015 Tectonophysics). For example, in an area called Chugoku region, the maximum and minimum compression axes were E-W and N-S directions, respectively. We also estimated the slip-deficit rate at the plate interface by analyzing GNSS data and calculated the stress fluctuation due to the deficit (e.g., Noda et al. 2013 GJI). The interplate locking causes the maximum compression in the direction of plate convergence. This is significantly different from the orientations of the background stress characterized by the E-W compressional strike-slip stress regime.. By combining the results of the background stress and the stress fluctuation, we made a map indicating the shear-strain energy change due to the interplate locking. In the Chugoku region, the shear-strain energy decreases due to the interplate locking. This is because the N-S compressional stress caused by the interplate locking compensates the N-S extensional stress in the background. The shear-strain energy increases in some parts of the analyzed areas. By statistically comparing the shear strain energy rate with the seismicity in the inland area, we found that the seismicity tends to be high where the interplate locking increases the shear-strain energy. Our results suggest that the stress fluctuation due to the interplate locking is not dominant in the background stress but surely contributes to the inland seismicity in southwest Japan.

Amorphization and Frictional Processes in Smectite-Quartz Gouge Mixtures Sheared from Sub-seismic to Seismic Slip Rates

NASA Astrophysics Data System (ADS)

Aretusini, S.; Mittempergher, S.; Spagnuolo, E.; Di Toro, G.; Gualtieri, A.; Plümper, O.

2015-12-01

Slipping zones in shallow sections of megathrusts and large landslides are often made of smectite and quartz gouge mixtures. Experiments aimed at investigating the frictional processes operating at high slip rates (>1 m/s) may unravel the mechanics of these natural phenomena. Here we present a new dataset obtained with two rotary shear apparatus (ROSA, Padua University; SHIVA, INGV-Rome). Experiments were performed at room humidity and temperature on four mixtures of smectite (Ca-Montmorillonite) and quartz with 68, 50, 25, 0 wt% of smectite. The gouges were slid for 3 m at normal stress of 5 MPa and slip rate V from 300 µm/s to 1.5 m/s. Temperature during the experiments was monitored with four thermocouples and modeled with COMSOL Multiphysics. In smectite-rich mixtures, the friction coefficient µ evolved with slip according to three slip rate regimes: in regime 1 (V<0.1 m/s) initial slip-weakening was followed by slip-strengthening; in regime 2 (0.10.3 m/s) µ had strong slip-weakening behavior. Instead, in quartz-rich mixtures the gouge had a monotonic slip-weakening behavior, independently of V. Temperature modelling showed that the fraction of work rate converted into heat decreased with increasing smectite content and slip rate. Quantitative X-ray powder diffraction (Rietveld method) indicates that the production of amorphous material from smectite breakdown increased with frictional work but was independent of work rate. Scanning Electron Microscopy investigation evidenced strain localization and presence of dehydrated clays for V≥0.3 m/s; instead, for V<0.3 m/s, strain was distributed and the gouge layer pervasively foliated. In conclusion, amorphization of the sheared gouges was not responsible of the measured frictional weakening. Instead, slip-weakening was concomitant to strain localization and possible vaporization of water adsorbed on smectite grain surfaces.

Source characteristics of the 2015 MW 7.8 Gorkha (Nepal) earthquake and its MW 7.2 aftershock from space geodesy

NASA Astrophysics Data System (ADS)

Feng, Wanpeng; Lindsey, Eric; Barbot, Sylvain; Samsonov, Sergey; Dai, Keren; Li, Peng; Li, Zhenhong; Almeida, Rafael; Chen, Jiajun; Xu, Xiaohua

2017-08-01

On April 25, 2015, a destructive MW 7.8 earthquake struck the capital of Nepal, Kathmandu, killing more than 8800 people and destroying numerous historical structures. We analyze six coseismic interferograms from several satellites (ALOS-2, Sentinel-1 A, and RADARSAT-2), as well as three-dimensional displacements at six GPS stations to investigate fault structure and slip distribution of the Gorkha earthquake. Using a layered crustal structure, the best-fit slip model shows that the preferred dip angle of the mainshock fault is 6 ± 3.5° and the major slip is concentrated within depths of 8-15 km. The maximum slip of 6.0 m occurs at a depth of 11 km, 70 km south east of the epicenter. The coseismic rupture extends 150 km eastward of the epicentre with a cumulative geodetic moment of 7.8 × 1020 Nm, equivalent to an earthquake of MW 7.84. We also investigate the MW 7.2 aftershock on 12 May 2015 using another three postseismic interferograms from ALOS2, RADARSAT-2, and Sentinel-1 A. The InSAR-based best-fit slip model of the largest aftershock implies that its major slip is next to the eastern lower end of the mainshock rupture with a similar maximum slip of 6 m at a depth of 13 km. This study generates various coseismic geodetic measurements to determine the source parameters of the MW 7.8 Gorkha earthquake and 12 May MW 7.2 afershock, providing an additional chance to understand the local fault structure and slip extent.

Inversion analysis of slip distribution of the 2008 Iwate-Miyagi Nairiku earthquake: Very high stress-drop or a conjugate fault slip?

NASA Astrophysics Data System (ADS)

Fukahata, Y.; Fukushima, Y.

2009-05-01

On 14 June 2008, the Iwate-Miyagi Nairiku earthquake struck northeast Japan, where active seismicity has been observed under east-west compressional stress fields. The magnitude and hypocenter depth of the earthquake are reported as Mj 7.2 and 8 km, respectively. The earthquake is considered to have occurred on a west-dipping reverse fault with a roughly north-south strike. The earthquake caused significant surface displacements, which were detected by PALSAR, a Synthetic Aperture Radar (SAR) onboard the Japanese ALOS satellite. Several pairs of PALSAR images from six different paths are available to measure the coseismic displacements. Interferometric SAR (InSAR) is useful to obtain crustal displacements in the region where coseismic displacement is not so large (less than 1 m), whereas range and azimuth offsets provide displacement measurements up to a few meters on the whole processed area. We inverted the obtained displacement data to estimate slip distribution on the fault. Since the precise location and direction of the fault are not well known, the inverse problem is nonlinear. Following the method of Fukahata and Wright (2008), we resolved the weak non-linearity based on Akaike's Bayesian Information Criterion. We first estimated slip distribution by assuming a pure dip slip. The optimal fault geometry was estimated at dip 26 and strike 203 degrees. The maximum slip is more than 8 m and most slips concentrate at shallow depths (less than 4 km). The azimuth offset data suggest non-negligible right lateral slip components, so we next estimated slip distribution without fixing the rake angle. Again, a large slip area with the maximum slip of about 8 m in the shallow depth was obtained. Such slip models contradict with our existing common sense; our results indicate that the released strain is more than 10 to the power of -3. Range and azimuth offsets computed from SAR images obtained from both ascending and descending orbits appear to be more consistent with a conjugate fault slip, which contributes to lower the stress drop possibly to a level typical to this kind of earthquakes.

Design study of steel V-Belt CVT for electric vehicles

NASA Technical Reports Server (NTRS)

Swain, J. C.; Klausing, T. A.; Wilcox, J. P.

1980-01-01

A continuously variable transmission (CVT) design layout was completed. The intended application was for coupling the flywheel to the driveline of a flywheel battery hybrid electric vehicle. The requirements were that the CVT accommodate flywheel speeds from 14,000 to 28,000 rpm and driveline speeds of 850 to 5000 rpm without slipping. Below 850 rpm a slipping clutch was used between the CVT and the driveline. The CVT was required to accommodate 330 ft-lb maximum torque and 100 hp maximum transient. The weighted average power was 22 hp, the maximum allowable full range shift time was 2 seconds and the required lift was 2600 hours. The resulting design utilized two steel V-belts in series to accommodate the required wide speed ratio. The size of the CVT, including the slipping clutch, was 20.6 inches long, 9.8 inches high and 13.8 inches wide. The estimated weight was 155 lb. An overall potential efficiency of 95 percent was projected for the average power condition.

The Mechanics of Transient Fault Slip and Slow Earthquakes

NASA Astrophysics Data System (ADS)

Marone, C.; Leeman, J.; Scuderi, M.; Saffer, D. M.; Collettini, C.

2015-12-01

Earthquakes are understood as frictional stick-slip instabilities in which stored elastic energy is released suddenly, driving catastrophic failure. In normal (fast) earthquakes the rupture zone expands at a rate dictated by elastic wave speeds, a few km/s, and fault slip rates reach 1-10 m/s. However, tectonic faults also fail in slow earthquakes with rupture durations of months and fault slip speeds of ~100 micron/s or less. We know very little about the mechanics of slow earthquakes. What determines the rupture propagation velocity in slow earthquakes and in other forms of quasi-dynamic rupture? What processes limit stress drop and fault slip speed in slow earthquakes? Existing lab studies provide some help via observations of complex forms of stick-slip, creep-slip, or, in a few cases, slow slip. However, these are mainly anecdotal and rarely include examples of repetitive slow slip or systematic measurements that could be used to isolate the underlying mechanisms. Numerical studies based on rate and state friction also shed light on transiently accelerating slip, showing that slow slip can occur if: 1) fault rheology involves a change in friction rate dependence (a-b) with velocity or unusually large values of the frictional weakening distance Dc, or 2) fault zone elastic stiffness equals the critical frictional weakening rate kc = (b-a)/Dc. Recent laboratory work shows that the latter can occur much more commonly that previously thought. We document the complete spectrum of stick-slip behaviors from transient slow slip to fast stick-slip for a narrow range of conditions around k/kc = 1.0. Slow slip occurs near the threshold between stable and unstable failure, controlled by the interplay of fault zone frictional properties, normal stress, and elastic stiffness of the surrounding rock. Our results provide a generic mechanism for slow earthquakes, consistent with the wide range of conditions for which slow slip has been observed.

Shape fabric development in rigid clast populations under pure shear: The influence of no-slip versus slip boundary conditions

NASA Astrophysics Data System (ADS)

Mulchrone, Kieran F.; Meere, Patrick A.

2015-09-01

Shape fabrics of elliptical objects in rocks are usually assumed to develop by passive behavior of inclusions with respect to the surrounding material leading to shape-based strain analysis methods belonging to the Rf/ϕ family. A probability density function is derived for the orientational characteristics of populations of rigid ellipses deforming in a pure shear 2D deformation with both no-slip and slip boundary conditions. Using maximum likelihood a numerical method is developed for estimating finite strain in natural populations deforming for both mechanisms. Application to a natural example indicates the importance of the slip mechanism in explaining clast shape fabrics in deformed sediments.

Focal mechanisms of recent earthquakes in the Southern Korean Peninsula

NASA Astrophysics Data System (ADS)

Park, Jong-Chan; Kim, Woohan; Chung, Tae Woong; Baag, Chang-Eob; Ree, Jin-Han

2007-06-01

We evaluate the stress field in and around the southern Korean Peninsula with focal mechanism solutions, using the data collected from 71 earthquakes (ML = 1.9-5.2) between 1999 and 2004. For this, the hypocentres were relocated and well-constrained fault plane solutions were obtained from the data set of 1270 clear P-wave polarities and 46 SH/P amplitude ratios. The focal mechanism solutions indicate that the prevailing faulting types in South Korea are strike-slip-dominant-oblique-slip faultings with minor reverse-slip component. The maximum principal stresses (σ1) estimated from fault-slip inversion analysis of the focal mechanism solutions show a similar orientation with E-W trend (269° -275°) and low-angle plunge (10° -25°) for all tectonic provinces in South Korea, consistent with the E-W trending maximum horizontal stress (σHmax) of the Amurian microplate reported from in situ stress measurements and earthquake focal mechanisms. The directions of the intermediate (σ2) and minimum (σ3) principal stresses of the Gyeongsang Basin are, however, about 90 deg off from those of the other tectonic provinces on a common σ2-σ3 plane, suggesting a permutation of σ2 and σ3. Our results incorporated with those from the kinematic studies of the Quaternary faults imply that NNW- to NE-striking faults (dextral strike-slip or oblique-slip with a reverse-slip component) are highly likely to generate earthquakes in South Korea.

Coseismic slip distribution of the February 27, 2010 Mw 8.9 Maule, Chile earthquake

USGS Publications Warehouse

Pollitz, Fred F.; Brooks, Ben; Tong, Xiaopeng; Bevis, Michael G.; Foster, James H.; Burgmann, Roland

2011-01-01

[1] Static offsets produced by the February 27, 2010 Mw = 8.8 Maule, Chile earthquake as measured by GPS and InSAR constrain coseismic slip along a section of the Andean megathrust of dimensions 650 km (in length) × 180 km (in width). GPS data have been collected from both campaign and continuous sites sampling both the near-field and far field. ALOS/PALSAR data from several ascending and descending tracks constrain the near-field crustal deformation. Inversions of the geodetic data for distributed slip on the megathrust reveal a pronounced slip maximum of order 15 m at ∼15–25 km depth on the megathrust offshore Lloca, indicating that seismic slip was greatest north of the epicenter of the bilaterally propagating rupture. A secondary slip maximum appears at depth ∼25 km on the megathrust just west of Concepción. Coseismic slip is negligible below 35 km depth. Estimates of the seismic moment based on different datasets and modeling approaches vary from 1.8 to 2.6 × 1022 N m. Our study is the first to model the static displacement field using a layered spherical Earth model, allowing us to incorporate both near-field and far-field static displacements in a consistent manner. The obtained seismic moment of 1.97 × 1022 N m, corresponding to a moment magnitude of 8.8, is similar to that obtained by previous seismic and geodetic inversions.

Intrinsic And Extrinsic Controls On Unsteady Deformation Rates, Northern Apennine Mountains, Italy

NASA Astrophysics Data System (ADS)

Anastasio, D. J.; Gunderson, K. L.; Pazzaglia, F. J.; Kodama, K. P.

2017-12-01

The slip rates of faults in the Northern Apennine Mountains were unsteady at 104-105 year timescales during the Neogene and Quaternary. Fault slip rates were recovered from growth strata and uplifted fluvial terraces associated with the Salsomaggiore, Quatto Castella, and Castevetro fault-related folds, sampled along the Stirone, Enza, and Panaro Rivers, respectively. The forelimb stratigraphy of each anticline was dated using rock magnetic-based cyclostratigraphy, which varies with Milankovitch periodicity, multispecies biostratigraphy, magnetostratigraphy, OSL luminescence dating, TCN burial dating, and radiocarbon dating of uplifted and folded fluvial terraces. Fault slip magnitudes were constrained with trishear forward models. We observed decoupled deformation and sediment accumulation rates at each structure. From 3.5Ma deformation of a thick and thin-skinned thrusts was temporally variable and controlled by intrinsic rock processes, whereas, the more regional Pede-Apenninic thrust fault, a thick-skinned thrust underlying the mountain front, was likely activated because of extrinsic forcing from foreland basin sedimentation rate accelerations since 1.4Ma. We found that reconstructed slip rate variability increased as the time resolution increased. The reconstructed slip history of the thin-skinned thrust faults was characterized relatively long, slow fold growth and associated fault slip, punctuated by shorter, more rapid periods limb rotation, and slip on the underlying thrust fault timed asynchronously. Thrust fault slip rates slip rates were ≤ 0.1 to 6 mm/yr at these intermediate timescales. The variability of slip rates on the thrusts is likely related to strain partitioning neighboring faults within the orogenic wedge. The studied structures slowed down at 1Ma when there was a switch to slower synchronous fault slip coincident with orogenic wedge thickening due to the emplacement of the out of sequence Pene-Apenninic thrust fault that was emplaced at 1.4±0.7 mm/yr. Both tectonic control and climate controlled variability on syntectonic sedimentation was observed in the growth sections.

Distribution of aseismic slip rate on the Hayward fault inferred from seismic and geodetic data

USGS Publications Warehouse

Schmidt, D.A.; Burgmann, R.; Nadeau, R.M.; d'Alessio, M.

2005-01-01

We solve for the slip rate distribution on the Hayward fault by performing a least squares inversion,of geodetic and seismic data sets. Our analysis focuses on the northern 60 km of the fault. Interferometric synthetic aperture radar (InSAR) data from 13 independent ERS interferograms are stacked to obtain range change rates from 1992 to 2000. Horizontal surface displacement rates at 141 bench marks are measured using GPS from 1994 to 2003. Surface creep observations and estimates of deep slip rates determined from characteristic repeating earthquake sequences are also incorporated in the inversion. The fault is discretized into 283 triangular dislocation elements that approximate the nonplanar attributes of the fault surface. South of the city of Hayward, a steeply, east dipping fault geometry accommodates the divergence of the surface trace and the microseismicity at depth. The inferred slip rate distribution is consistent with a fault that creeps aseismically at a rate of ???5 mm/yr to a depth of 4-6 km. The interferometric synthetic aperture radar (InSAR) data require an aseismic slip rate that approaches the geologic slip rate on the northernmost fault segment beneath Point Pinole, although the InSAR data might be complicated by a small dip-slip component at this location. A low slip rate patch of <1 mm/yr is inferred beneath San Leandro consistent with the source location of the 1868 earthquake. We calculate that the entire fault is accumulating a slip rate deficit equivalent to a Mw = 6.77 ?? 0.05 per century. However, this estimate of potential coseismic moment represents an upper bound because we do not know how much of the accumulated strain will be released through aseismic processes such as afterslip. Copyright 2005 by the American Geophysical Union.

Evidence for a high slip rate of the Calico fault in the Eastern California Shear Zone

NASA Astrophysics Data System (ADS)

Xie, S.; Wetmore, P. H.; Owen, L. A.; Gallant, E.; Dixon, T. H.

2016-12-01

Fault slip rates provide important constraint on seismic hazard assessments. Geologic and geodetic estimates of slip rates across the Eastern California Shear Zone (ECSZ) reveal a discrepancy between the two data sets. Most studies attempting to reconcile the discrepancy have focused on off-fault deformation and the technique limitation of short-term geodetic measurements, while there is less concern about the relatively small number of cited geologic slip rates. The Calico fault is central fault in the Mojave Desert portion of the ECSZ, where published geologic slip rates are between 1 and 2 mm/yr. We determine new geologic slip rates of the Calico fault by dating two offset alluvial fans near the town of Newberry Springs, California. Correlation of the offset fans was based on geomorphic and soil development characteristics. Offset magnitudes are based on high-resolution topography and orthoimagery, and by cropping and matching the alluvial fans along the fault trace. Surface displacements of the two offset fans are 80 m and 1120 m. Surface exposure ages of alluvial fan samples are dated using the production of 10Be terrestrial cosmogenic nuclide (TCN). The fan with an 80 m offset produced an age of 40 ka, yielding a slip rate of 2 mm/yr, consistent with previous studies. The fan with displacement of 1120 m produced an age of 290 ka, yielding a slip rate of 4 mm/yr, indicating that the Calico fault likely had a much higher slip rate early and has decreased more recently.

Slip and Dilation Tendency Analysis of the San Emidio Geothermal Area

DOE Data Explorer

Faulds, James E.

2013-12-31

Critically stressed fault segments have a relatively high likelihood of acting as fluid flow conduits (Sibson, 1994). As such, the tendency of a fault segment to slip (slip tendency; Ts; Morris et al., 1996) or to dilate (dilation tendency; Td; Ferrill et al., 1999) provides an indication of which faults or fault segments within a geothermal system are critically stressed and therefore likely to transmit geothermal fluids. The slip tendency of a surface is defined by the ratio of shear stress to normal stress on that surface: Ts = τ / σn (Morris et al., 1996). Dilation tendency is defined by the stress acting normal to a given surface: Td = (σ1-σn) / (σ1-σ3) (Ferrill et al., 1999). Slip and dilation were calculated using 3DStress (Southwest Research Institute). Slip and dilation tendency are both unitless ratios of the resolved stresses applied to the fault plane by ambient stress conditions. Values range from a maximum of 1, a fault plane ideally oriented to slip or dilate under ambient stress conditions to zero, a fault plane with no potential to slip or dilate. Slip and dilation tendency values were calculated for each fault in the focus study areas at, McGinness Hills, Neal Hot Springs, Patua, Salt Wells, San Emidio, and Tuscarora on fault traces. As dip is not well constrained or unknown for many faults mapped in within these we made these calculations using the dip for each fault that would yield the maximum slip tendency or dilation tendency. As such, these results should be viewed as maximum tendency of each fault to slip or dilate. The resulting along-fault and fault-to-fault variation in slip or dilation potential is a proxy for along fault and fault-to-fault variation in fluid flow conduit potential. Stress Magnitudes and directions Stress field variation within each focus area was approximated based on regional published data and the world stress database (Hickman et al., 2000; Hickman et al., 1998 Robertson-Tait et al., 2004; Hickman and Davatzes, 2010; Davatzes and Hickman, 2006; Blake and Davatzes 2011; Blake and Davatzes, 2012; Moeck et al., 2010; Moos and Ronne, 2010 and Reinecker et al., 2005) as well as local stress information if applicable. For faults within these focus systems we applied either a normal faulting stress regime where the vertical stress (sv) is larger than the maximum horizontal stress (shmax) which is larger than the minimum horizontal stress (sv>shmax>shmin) or strike-slip faulting stress regime where the maximum horizontal stress (shmax) is larger than the vertical stress (sv) which is larger than the minimum horizontal stress (shmax >sv>shmin) depending on the general tectonic province of the system. Based on visual inspection of the limited stress magnitude data in the Great Basin we used magnitudes such that shmin/shmax = .527 and shmin/sv= .46, which are consistent with complete and partial stress field determinations from Desert Peak, Coso, the Fallon area and Dixie valley (Hickman et al., 2000; Hickman et al., 1998 Robertson-Tait et al., 2004; Hickman and Davatzes, 2011; Davatzes and Hickman, 2006; Blake and Davatzes 2011; Blake and Davatzes, 2012). Slip and dilation tendency for the San Emidio geothermal field was calculated based on the faults mapped Tuscarora area (Rhodes, 2011). The San Emidio area lies in the Basin and Range Province, as such we applied a normal faulting stress regime to the San Emidio area faults, with a minimum horizontal stress direction oriented 115, based on inspection of local and regional stress determinations, as explained above. This is consistent with the shmin determined through inversion of fault data by Rhodes (2011). Under these stress conditions north-northeast striking, steeply dipping fault segments have the highest dilation tendency, while north-northeast striking 60° dipping fault segments have the highest tendency to slip. Interesting, the San Emidio geothermal field lies in an area of primarily north striking faults, which...

Slip and Dilation Tendency Analysis of the Salt Wells Geothermal Area

DOE Data Explorer

Faulds, James E.

2013-12-31

Critically stressed fault segments have a relatively high likelihood of acting as fluid flow conduits (Sibson, 1994). As such, the tendency of a fault segment to slip (slip tendency; Ts; Morris et al., 1996) or to dilate (dilation tendency; Td; Ferrill et al., 1999) provides an indication of which faults or fault segments within a geothermal system are critically stressed and therefore likely to transmit geothermal fluids. The slip tendency of a surface is defined by the ratio of shear stress to normal stress on that surface: Ts = τ / σn (Morris et al., 1996). Dilation tendency is defined by the stress acting normal to a given surface: Td = (σ1-σn) / (σ1-σ3) (Ferrill et al., 1999). Slip and dilation were calculated using 3DStress (Southwest Research Institute). Slip and dilation tendency are both unitless ratios of the resolved stresses applied to the fault plane by ambient stress conditions. Values range from a maximum of 1, a fault plane ideally oriented to slip or dilate under ambient stress conditions to zero, a fault plane with no potential to slip or dilate. Slip and dilation tendency values were calculated for each fault in the focus study areas at, McGinness Hills, Neal Hot Springs, Patua, Salt Wells, San Emidio, and Tuscarora on fault traces. As dip is not well constrained or unknown for many faults mapped in within these we made these calculations using the dip for each fault that would yield the maximum slip tendency or dilation tendency. As such, these results should be viewed as maximum tendency of each fault to slip or dilate. The resulting along-fault and fault-to-fault variation in slip or dilation potential is a proxy for along fault and fault-to-fault variation in fluid flow conduit potential. Stress Magnitudes and directions Stress field variation within each focus area was approximated based on regional published data and the world stress database (Hickman et al., 2000; Hickman et al., 1998 Robertson-Tait et al., 2004; Hickman and Davatzes, 2010; Davatzes and Hickman, 2006; Blake and Davatzes 2011; Blake and Davatzes, 2012; Moeck et al., 2010; Moos and Ronne, 2010 and Reinecker et al., 2005) as well as local stress information if applicable. For faults within these focus systems we applied either a normal faulting stress regime where the vertical stress (sv) is larger than the maximum horizontal stress (shmax) which is larger than the minimum horizontal stress (sv>shmax>shmin) or strike-slip faulting stress regime where the maximum horizontal stress (shmax) is larger than the vertical stress (sv) which is larger than the minimum horizontal stress (shmax >sv>shmin) depending on the general tectonic province of the system. Based on visual inspection of the limited stress magnitude data in the Great Basin we used magnitudes such that shmin/shmax = .527 and shmin/sv= .46, which are consistent with complete and partial stress field determinations from Desert Peak, Coso, the Fallon area and Dixie valley (Hickman et al., 2000; Hickman et al., 1998 Robertson-Tait et al., 2004; Hickman and Davatzes, 2011; Davatzes and Hickman, 2006; Blake and Davatzes 2011; Blake and Davatzes, 2012). Slip and dilation tendency for the Salt Wells geothermal field was calculated based on the faults mapped in the Bunejug Mountains quadrangle (Hinz et al., 2011). The Salt Wells area lies in the Basin and Range Province (N. Hinz personal comm.) As such we applied a normal faulting stress regime to the Salt Wells area faults, with a minimum horizontal stress direction oriented 105, based on inspection of local and regional stress determinations. Under these stress conditions north-northeast striking, steeply dipping fault segments have the highest dilation tendency, while north-northeast striking 60° dipping fault segments have the highest tendency to slip. Several such faults intersect in high density in the core of the accommodation zone in the Bunejug Mountains and local to the Salt Wells geothermal .

Vitrinite reflectance and Raman spectra of carbonaceous material as indicators of frictional heating on faults: Constraints from friction experiments

NASA Astrophysics Data System (ADS)

Furuichi, Hiroyuki; Ujiie, Kohtaro; Kouketsu, Yui; Saito, Tsubasa; Tsutsumi, Akito; Wallis, Simon

2015-08-01

Vitrinite reflectance (Ro) and Raman spectra of carbonaceous material (RSCM) are both widely used as indicators of the maximum attained temperatures in sedimentary and metamorphic rocks. However, the potential of these methods to estimate temperature increases associated with fault slip has not been closely studied. To examine this issue, friction experiments were conducted on a mixture of powdered clay-rich fault material and carbonaceous material (CM) at slip rates of 0.15 mm/s and 1.3 m/s in nitrogen (N2) gas with or without distilled water. After the experiments, we measured Ro and RSCM and compared to those in starting material. The results indicate that when fault material suffers rapid heating at >500 °C in ∼9 s at 1.3 m/s, Ro and the intensity ratio of D1 and D2 Raman bands of CM (ID2/ID1) markedly increase. Comminution with very small temperature rise in ∼32 min at 0.15 mm/s is responsible for very limited changes in Ro and ID2/ID1. Our results demonstrate that Ro and RSCM could be useful for the detection of frictional heating on faults when the power density is ≥0.52 MW/m2. However, the conventionally used Ro and RSCM geothermometers are inadequate for the estimation of peak temperature during seismic fault slip. The reaction kinetics incorporating the effects of rapid heating at high slip rates and studies of the original microtexture and composition of CM are required to establish a reliable thermometer for frictional heating on faults.

Late Quaternary slip rate determination by CRN dating on the Haiyuan fault, China, and implication for complex geometry fault systems

NASA Astrophysics Data System (ADS)

Matrau, Rémi; Klinger, Yann; Van der Woerd, Jérôme; Liu-Zeng, Jing; Li, Zhanfei; Xu, Xiwei

2017-04-01

Late Quaternary slip rate determination by CRN dating on the Haiyuan fault, China, and implication for complex geometry fault systems Matrau Rémi, Klinger Yann, Van der Woerd Jérôme, Liu-Zeng Jing, Li Zhanfei, Xu Xiwei The Haiyuan fault in Gansu Province, China, is a major left-lateral strike-slip fault forming the northeastern boundary of the Tibetan plateau and accommodating part of the deformation from the India-Asia collision. Geomorphic and geodetic studies of the Haiyuan fault show slip rates ranging from 4 mm/yr to 19 mm/yr from east to west along 500 km of the fault. Such discrepancy could be explained by the complex geometry of the fault system, leading to slip distribution on multiple branches. Combining displacement measurements of alluvial terraces from high-resolution Pléiades images and 10Be - 26Al cosmogenic radionuclides (CRN) dating, we bracket the late Quaternary slip rate along the Hasi Shan fault segment (37°00' N, 104°25' E). At our calibration site, terrace riser offsets for 5 terraces ranging from 6 m to 227 m and CRN ages ranging from 6.5±0.6 kyr to 41±4 kyr - yield geological left-lateral slip rates from 2.0 mm/yr to 4.4 mm/yr. We measured consistent terrace riser offset values along the entire 25 km-long segment, which suggests that some external forcing controls the regional river-terrace emplacement, regardless of each specific catchment. Hence, we extend our slip rate determination to the entire Hasi Shan fault segment to be 4.0±1.0 mm/yr since the last 40 kyr. This rate is consistent with other long-term rates of 4 mm/yr to 5 mm/yr east and west of Hasi Shan - as well as geodetic rates of 4 mm/yr to 6 mm/yr west of Hasi Shan. However, Holocene terraces and moraines offsets have suggested higher rates of 15 to 20 mm/yr further west. Such disparate rates may be explained by slip distribution on multiple branches. In particular, the Zhongwei fault splay in the central part of the Haiyuan fault, with a slip rate of 4-5 mm/yr could partly explain the faster rates on the western single stranded Haiyuan fault. In addition we constrained 0.55±0.1 mm/yr of uplift rate along the Hasi Shan, where the fault strike veers southward, indicating slip partitioning. Our slip rate along the Hasi Shan segment is consistent with most of the long-term and short-term slip rates ( 5 mm/yr) measured along the central and eastern parts of the Haiyuan fault. However the discrepancy with other studies to the west highlights the major implication of complex geometries on the slip distribution over large fault systems.

Late Holocene slip rate of the San Andreas fault and its accommodation by creep and moderate-magnitude earthquakes at Parkfield, California

USGS Publications Warehouse

Toke, N.A.; Arrowsmith, J.R.; Rymer, M.J.; Landgraf, A.; Haddad, D.E.; Busch, M.; Coyan, J.; Hannah, A.

2011-01-01

Investigation of a right-laterally offset channel at the Miller's Field paleoseismic site yields a late Holocene slip rate of 26.2 +6.4/-4.3 mm/yr (1??) for the main trace of the San Andreas fault at Park-field, California. This is the first well-documented geologic slip rate between the Carrizo and creeping sections of the San Andreas fault. This rate is lower than Holocene measurements along the Carrizo Plain and rates implied by far-field geodetic measurements (~35 mm/yr). However, the rate is consistent with historical slip rates, measured to the northwest, along the creeping section of the San Andreas fault (<30 mm/yr). The paleoseismic exposures at the Miller's Field site reveal a pervasive fabric of clay shear bands, oriented clockwise oblique to the San Andreas fault strike and extending into the upper-most stratigraphy. This fabric is consistent with dextral aseismic creep and observations of surface slip from the 28 September 2004 M6 Parkfield earthquake. Together, this slip rate and deformation fabric suggest that the historically observed San Andreas fault slip behavior along the Parkfield section has persisted for at least a millennium, and that significant slip is accommodated by structures in a zone beyond the main San Andreas fault trace. ?? 2011 Geological Society of America.

Dynamic rupture modeling with laboratory-derived constitutive relations

USGS Publications Warehouse

Okubo, P.G.

1989-01-01

A laboratory-derived state variable friction constitutive relation is used in the numerical simulation of the dynamic growth of an in-plane or mode II shear crack. According to this formulation, originally presented by J.H. Dieterich, frictional resistance varies with the logarithm of the slip rate and with the logarithm of the frictional state variable as identified by A.L. Ruina. Under conditions of steady sliding, the state variable is proportional to (slip rate)-1. Following suddenly introduced increases in slip rate, the rate and state dependencies combine to produce behavior which resembles slip weakening. When rupture nucleation is artificially forced at fixed rupture velocity, rupture models calculated with the state variable friction in a uniformly distributed initial stress field closely resemble earlier rupture models calculated with a slip weakening fault constitutive relation. Model calculations suggest that dynamic rupture following a state variable friction relation is similar to that following a simpler fault slip weakening law. However, when modeling the full cycle of fault motions, rate-dependent frictional responses included in the state variable formulation are important at low slip rates associated with rupture nucleation. -from Author

Variable slip-rate and slip-per-event on a plate boundary fault: The Dead Sea fault in northern Israel

NASA Astrophysics Data System (ADS)

Wechsler, Neta; Rockwell, Thomas K.; Klinger, Yann

2018-01-01

We resolved displacement on buried stream channels that record the past 3400 years of slip history for the Jordan Gorge (JGF) section of the Dead Sea fault in Israel. Based on three-dimensional (3D) trenching, slip in the past millennium amounts to only 2.7 m, similar to that determined in previous studies, whereas the previous millennium experienced two to three times this amount of displacement with nearly 8 m of cumulative slip, indicating substantial short term variations in slip rate. The slip rate averaged over the past 3400 years, as determined from 3D trenching, is 4.1 mm/yr, which agrees well with geodetic estimates of strain accumulation, as well as with longer-term geologic slip rate estimates. Our results indicate that: 1) the past 1200 years appear to significantly lack slip, which may portend a significant increase in future seismic activity; 2) short-term slip rates for the past two millennia have varied by more than a factor of two and suggest that past behavior is best characterized by clustering of earthquakes. From these observations, the earthquake behavior of the Jordan Gorge fault best fits is a "weak segment model" where the relatively short fault section (20 km), bounded by releasing steps, fails on its own in moderate earthquakes, or ruptures with adjacent segments.

Coseismic and Afterslip Model Related to 25 April 2015, Mw7.8 Gorkha, Nepal Earthquake and its Potential Future Risk Regions

NASA Astrophysics Data System (ADS)

Wang, S.; Xu, C.; Jiang, G.

2016-12-01

Evidences from geologic, geophysical and geomorphic prove that 2015 Mw 7.8 Gorkha(Nepal) earthquake happened on the two ramp-flats fault structure of Main Himalayan Thrust(MHT). We approximated this more realistic fault model by a smooth curved fault surface, which was derived by the method of hybrid iterative inversion algorithm(HIIA) with additional constraints from coseismic geodetic data. Then the coseismic slip distribution of 2015 Gorkha earthquake was imaged based on this curved variably triangular sized fault model. The inverted maximum thrust and right-lateral slip components are 6 and 1.5 m, respectively, with the maximum slip magnitude 6.2 m located at a depth of 15 km. The released seismic moment derived from our best slip model is 8.58×1020 Nm, equivalent to a moment magnitude of Mw 7.89. We find two interesting tongue-shape slip areas, the maximum slip is about 1.5 m, along the up-dip of fault plane, which tappers off at the depth of 7 km, the up-dip propagation of ruptures may be impeded by the complicated geometry structures on the MHT interface. Coulomb Failure Stress(CFS), triggered by our optimal slip model, indicating a potential shallower rupture in the future. Considering historical earthquakes distribution and the calculated strain and strain gradient before this earthquake, earthquakes are expected to occur in the northwest areas of the epicenter. The spatio-temporal afterslip model over the first 180 days following the Mw 7.8 main shock was infered from the post-seismic GPS time series. One significant afterslip region can be observed in the downdip of the regions that ruptured by coseismic slip. Another afterslip region arresting our attention, is located around 40 km depth, with about 180 mm slip amplitude, but tappers off at the depth of 50 km. What's more, afterslip mainly occurs within 100 days after the 2015 Gorkha earthquake. Under the assumption of rigidity modulus u = 30 GPa, the released seismic moment by afterslip corresponding to 8.0×1019 Nm, equivalent moment magnitude is Mw 7.23. Our coseismic and afterslip models are in line with previous studies, but with a more accurate geometric fault model.

Effects of isotropic and anisotropic slip on droplet impingement on a superhydrophobic surface

NASA Astrophysics Data System (ADS)

Clavijo, Cristian E.; Crockett, Julie; Maynes, Daniel

2015-12-01

The dynamics of single droplet impingement on micro-textured superhydrophobic surfaces with isotropic and anisotropic slip are investigated. While several analytical models exist to predict droplet impact on superhydrophobic surfaces, no previous model has rigorously considered the effect of the shear-free region above the gas cavities resulting in an apparent slip that is inherent for many of these surfaces. This paper presents a model that accounts for slip during spreading and recoiling. A broad range of Weber numbers and slip length values were investigated at low Ohnesorge numbers. The results show that surface slip exerts negligible influence throughout the impingement process for low Weber numbers but can exert significant influence for high Weber numbers (on the order of 102). When anisotropic slip prevails, the droplet exhibits an elliptical shape at the point of maximum spread, with greater eccentricity for increasing slip and increasing Weber number. Experiments were performed on isotropic and anisotropic micro-structured superhydrophobic surfaces and the agreement between the experimental results and the model is very good.

Paleomagnetic, structural, and seismological evidence for oblique-slip deformation in fault-related folds in the Rocky Mountain Foreland, Colorado Plateau, and central Coast Ranges

NASA Astrophysics Data System (ADS)

Tetreault, Joya Liana

The two geologic questions I address in this research are: do fault-related folds accommodate oblique-slip shortening, and how is oblique-slip deformation absorbed within the folded strata? If the strata is deforming as a strike-slip shear zone, then we should be able to observe material rotations produced by strike-slip shear by measuring paleomagnetic vertical-axis rotations. I have approached these problems by applying paleomagnetic vertical-axis rotations, minor fault analyses, and focal mechanism strain inversions to identify evidence of strike-slip shear and to quantify oblique-slip deformation within fault-related folds in the Rocky Mountain Foreland, Colorado Plateau, and the central Coast Ranges. Clockwise paleomagnetic vertical-axis rotations and compressive paleostress rotations of 15-40º in the forelimb of the Grayback Monocline, northeastern Front Range Colorado, indicate that this Laramide fold is absorbing right-lateral shear from a N90E regional shortening direction. This work shows that paleomagnetic vertical-axis rotations in folded strata can be used to identify strike-slip motion on an underlying fault, and that oblique-slip deformation is localized in the forelimb of the fold. I applied the same paleomagnetic methods to identify oblique-slip on the underlying faults of the Nacimiento, East Kaibab, San Rafael, and Grand Hogback monoclines of the Colorado Plateau. The absence of paleomagnetic rotations and structural evidence for small displacements at the Nacimiento and East Kaibab monoclines indicate minor (<1km) right-lateral slip is being accommodated in these folds. Paleomagnetic vertical-axis rotations are found in the forelimbs of the San Rafael and Grand Hogback monoclines, yielding strike-slip displacements of ˜5km within these two folds. These results are consistent with a northeast Laramide compressive stress direction. In the Coalinga anticline, central Coast Ranges, California, clockwise paleomagnetic rotations and an 8º counterclockwise deflection of the maximum shortening direction (derived from focal mechanisms strain inversions of the upper 7km) are compatible with right-lateral shear. The maximum shortening direction in the area of the mainshock rupture is fold-normal, indicating that strike-slip displacement is confined to the main fault plane and not distributed to the hanging wall. The San Andreas Fault is therefore partitioning a small amount of strike-slip to the Coalinga anticline.

Does fault strengthening in laboratory rock friction experiments really depend primarily upon time and not slip?

NASA Astrophysics Data System (ADS)

Bhattacharya, Pathikrit; Rubin, Allan M.; Beeler, Nicholas M.

2017-08-01

The popular constitutive formulations of rate-and-state friction offer two end-member views on whether friction evolves only with slip (Slip law) or with time even without slip (Aging law). While rate stepping experiments show support for the Slip law, laboratory-observed frictional behavior near-zero slip rates has traditionally been inferred as supporting Aging law style time-dependent healing, in particular, from the slide-hold-slide experiments of Beeler et al. (1994). Using a combination of new analytical results and explicit numerical (Bayesian) inversion, we show instead that the slide-hold-slide data of Beeler et al. (1994) favor slip-dependent state evolution during holds. We show that, while the stiffness-independent rate of growth of peak stress (following reslides) with hold duration is a property shared by both the Aging and (under a more restricted set of parameter combinations) Slip laws, the observed stiffness dependence of the rate of stress relaxation during long holds is incompatible with the Aging law with constant rate-state parameters. The Slip law consistently fits the evolution of the stress minima at the end of the holds well, whether fitting jointly with peak stresses or otherwise. But neither the Aging nor Slip laws fit all the data well when a - b is constrained to values derived from prior velocity steps. We also attempted to fit the evolution of stress peaks and minima with the Kato-Tullis hybrid law and the shear stress-dependent Nagata law, both of which, even with the freedom of an extra parameter, generally reproduced the best Slip law fits to the data.

Viscous Moment, Mechanism of Slow Slip, and Subduction Megathrust Viscosity

NASA Astrophysics Data System (ADS)

Fagereng, A.

2015-12-01

Slow slip events (SSEs) represent transient slip velocities slower than earthquakes but faster than steady, average plate motion. SSEs repeating at the same location have characteristic slip magnitude and duration. Contrary to earthquakes, however, average slip relates to neither duration nor area. Variations in duration, slip, and slip rate can instead be tied to variations in effective viscosity, calculated from a viscous definition of moment. In this paradigm, the observation that deep slow slip events are slower and longer, implies a higher effective viscosity than in shallower, colder SSEs. Observed variations in effective viscosity and slip rate can be interpreted in terms of differences in driving stress and shear zone width, and likely arise in anastomosing shear zones containing a heterogeneous mixture of materials.

The last interglacial period at Guantanamo Bay, Cuba and an estimate of late Quaternary tectonic uplift rate in a strike-slip regime

NASA Astrophysics Data System (ADS)

Schweig, E. S.; Muhs, D. R.; Simmons, K. R.; Halley, R. B.

2015-12-01

Guantanamo Bay, Cuba is an area dominated by a strike-slip tectonic regime and is therefore expected to have very low Quaternary uplift rates. We tested this hypothesis by study of an unusually well preserved emergent reef terrace around the bay. Up to 12 m of unaltered, growth-position reef corals are exposed at about 40 sections examined around ˜40 km of coastline. Maximum reef elevations in the protected, inner part of the bay are ˜11-12 m, whereas outer-coast shoreline angles of wave-cut benches are as high as ˜14 m. Fifty uranium-series analyses of unrecrystallized corals from six localities yield ages ranging from ˜134 ka to ˜115 ka, when adjusted for small biases due to slightly elevated initial 234U/238U values. Thus, ages of corals correlate this reef to the peak of the last interglacial period, marine isotope stage (MIS) 5.5. Previously, we dated the Key Largo Limestone to the same high-sea stand in the tectonically stable Florida Keys. Estimates of paleo-sea level during MIS 5.5 in the Florida Keys are ~6.6 to 8.3 m above present. Assuming a similar paleo-sea level in Cuba, this yields a long-term tectonic uplift rate of 0.04-0.06 m/ka over the past ~120 ka. This estimate supports the hypothesis that the tectonic uplift rate should be low in this strike-slip regime. Nevertheless, on the southeast coast of Cuba, east of our study area, we have observed flights of multiple marine terraces, suggesting either (1) a higher uplift rate or (2) an unusually well-preserved record of pre-MIS 5.5 terraces not observed at Guantanamo Bay.

Simulated tsunami inundation for a range of Cascadia megathrust earthquake scenarios at Bandon, Oregon, USA

USGS Publications Warehouse

Witter, Robert C.; Zhang, Yinglong J.; Wang, Kelin; Priest, George R.; Goldfinger, Chris; Stimely, Laura; English, John T.; Ferro, Paul A.

2013-01-01

Characterizations of tsunami hazards along the Cascadia subduction zone hinge on uncertainties in megathrust rupture models used for simulating tsunami inundation. To explore these uncertainties, we constructed 15 megathrust earthquake scenarios using rupture models that supply the initial conditions for tsunami simulations at Bandon, Oregon. Tsunami inundation varies with the amount and distribution of fault slip assigned to rupture models, including models where slip is partitioned to a splay fault in the accretionary wedge and models that vary the updip limit of slip on a buried fault. Constraints on fault slip come from onshore and offshore paleoseismological evidence. We rank each rupture model using a logic tree that evaluates a model’s consistency with geological and geophysical data. The scenarios provide inputs to a hydrodynamic model, SELFE, used to simulate tsunami generation, propagation, and inundation on unstructured grids with <5–15 m resolution in coastal areas. Tsunami simulations delineate the likelihood that Cascadia tsunamis will exceed mapped inundation lines. Maximum wave elevations at the shoreline varied from ∼4 m to 25 m for earthquakes with 9–44 m slip and Mw 8.7–9.2. Simulated tsunami inundation agrees with sparse deposits left by the A.D. 1700 and older tsunamis. Tsunami simulations for large (22–30 m slip) and medium (14–19 m slip) splay fault scenarios encompass 80%–95% of all inundation scenarios and provide reasonable guidelines for land-use planning and coastal development. The maximum tsunami inundation simulated for the greatest splay fault scenario (36–44 m slip) can help to guide development of local tsunami evacuation zones.

Tsunamis from strike-slip earthquakes in the Wharton Basin, northeast Indian Ocean: March 2016 Mw7.8 event and its relationship with the April 2012 Mw 8.6 event

NASA Astrophysics Data System (ADS)

Heidarzadeh, Mohammad; Harada, Tomoya; Satake, Kenji; Ishibe, Takeo; Takagawa, Tomohiro

2017-12-01

The Wharton Basin, off southwest Sumatra, ruptured to a large intraplate left-lateral strike-slip Mw 7.8 earthquake on 2016 March 2. The epicentre was located ∼800 km to the south of another similar-mechanism intraplate Mw 8.6 earthquake in the same basin on 2012 April 11. Small tsunamis from these strike-slip earthquakes were registered with maximum amplitudes of 0.5-1.5 cm on DARTs and 1-19 cm on tide gauges for the 2016 event, and the respective values of 0.5-6 and 6-40 cm for the 2012 event. By using both teleseismic body waves and tsunami observations of the 2016 event, we obtained optimum slip models with rupture velocity (Vr) in the range of 2.8-3.6 km s-1 belonging to both EW and NS faults. While the EW fault plane cannot be fully ruled out, we chose the best model as the NS fault plane with a Vr of 3.6 km s-1, a maximum slip of 7.7 m and source duration of 33 s. The tsunami energy period bands were 4-15 and 7-24 min for the 2016 and 2012 tsunamis, respectively, reflecting the difference in source sizes. Seismicity in the Wharton Basin is dominated by large strike-slip events including the 2012 (Mw 8.6 and 8.2) and 2016 (Mw 7.8) events, indicating that these events are possible tsunami sources in the Wharton Basin. Cumulative number and cumulative seismic-moment curves revealed that most earthquakes are of strike-slip mechanisms and the largest seismic-moment is provided by the strike-slip earthquakes in this basin.

A New Geological Slip Rate Estimate for the Calico Fault, Eastern California: Implications for Geodetic Versus Geologic Rate Estimates in the Eastern California Shear Zone

NASA Astrophysics Data System (ADS)

Wetmore, P. H.; Xie, S.; Gallant, E.; Owen, L. A.; Dixon, T. H.

2017-12-01

Fault slip rate is fundamental to accurate seismic hazard assessment. In the Mojave Desert section of the Eastern California Shear Zone previous studies have suggested a discrepancy between short-term geodetic and long-term geologic slip rate estimates. Understanding the origin of this discrepancy could lead to better understanding of stress evolution, and improve earthquake hazard estimates in general. We measured offsets in alluvial fans along the Calico fault near Newberry Springs, California, and used exposure age dating based on the cosmogenic nuclide 10Be to date the offset landforms. We derive a mean slip rate of 3.6 mm/yr, representing an average over the last few hundred thousand years, significantly faster than previous estimates. Considering numerous faults in the Mojave Desert and limited geologic slip rate estimates, it is premature to claim a geologic versus geodetic "discrepancy" for the ECSZ. More slip rate data, from all faults with the ECSZ, are needed to provide a statistically meaningful assessment of the geologic rates for each of the faults comprising the ECSZ.

Laboratory constraints on models of earthquake recurrence

NASA Astrophysics Data System (ADS)

Beeler, N. M.; Tullis, Terry; Junger, Jenni; Kilgore, Brian; Goldsby, David

2014-12-01

In this study, rock friction "stick-slip" experiments are used to develop constraints on models of earthquake recurrence. Constant rate loading of bare rock surfaces in high-quality experiments produces stick-slip recurrence that is periodic at least to second order. When the loading rate is varied, recurrence is approximately inversely proportional to loading rate. These laboratory events initiate due to a slip-rate-dependent process that also determines the size of the stress drop and, as a consequence, stress drop varies weakly but systematically with loading rate. This is especially evident in experiments where the loading rate is changed by orders of magnitude, as is thought to be the loading condition of naturally occurring, small repeating earthquakes driven by afterslip, or low-frequency earthquakes loaded by episodic slip. The experimentally observed stress drops are well described by a logarithmic dependence on recurrence interval that can be cast as a nonlinear slip predictable model. The fault's rate dependence of strength is the key physical parameter. Additionally, even at constant loading rate the most reproducible laboratory recurrence is not exactly periodic, unlike existing friction recurrence models. We present example laboratory catalogs that document the variance and show that in large catalogs, even at constant loading rate, stress drop and recurrence covary systematically. The origin of this covariance is largely consistent with variability of the dependence of fault strength on slip rate. Laboratory catalogs show aspects of both slip and time predictability, and successive stress drops are strongly correlated indicating a "memory" of prior slip history that extends over at least one recurrence cycle.

Preventing Slips and Falls through Leisure-Time Physical Activity: Findings from a Study of Limited-Service Restaurants

PubMed Central

Caban-Martinez, Alberto J.; Courtney, Theodore K.; Chang, Wen-Ruey; Lombardi, David A.; Huang, Yueng-Hsiang; Brennan, Melanye J.; Perry, Melissa J.; Katz, Jeffrey N.; Verma, Santosh K.

2014-01-01

Background/Objective Physical activity has been shown to be beneficial at improving health in some medical conditions and in preventing injury. Epidemiologic studies suggest that physical activity is one factor associated with a decreased risk for slips and falls in the older (≥65 years) adult population. While the risk of slips and falls is generally lower in younger than in older adults; little is known of the relative contribution of physical activity in preventing slips and falls in younger adults. We examined whether engagement in leisure-time physical activity (LTPA) was protective of slips and falls among a younger/middle-aged (≤50 years old) working population. Methods 475 workers from 36 limited-service restaurants in six states in the U.S. were recruited to participate in a prospective cohort study of workplace slipping. Information on LTPA was collected at the time of enrollment. Participants reported their slip experience and work hours weekly for up to 12 weeks. We investigated the association between the rate of slipping and the rate of major slipping (i.e., slips that resulted in a fall and/or injury) and LTPA for workers 50 years of age and younger (n = 433, range 18–50 years old) using a multivariable negative binomial generalized estimating equation model. Results The rate of major slips among workers who engaged in moderate (Adjusted Rate Ratio (RR)  = 0.65; 95% Confidence Interval (CI)  =  [0.18–2.44]) and vigorous (RR = 0.64; 95%CI  =  [0.18–2.26]) LTPA, while non-significant, were approximately one-third lower than the rate of major slips among less active workers. Conclusion While not statistically significant, the results suggest a potential association between engagement in moderate and vigorous LTPA and the rate of major slips in younger adults. Additional studies that examine the role of occupational and non-occupational physical activity on the risk of slips, trips and falls among younger and middle aged adults appear warranted. PMID:25329816

Estimating Stresses, Fault Friction and Fluid Pressure from Topography and Coseismic Slip Models

NASA Astrophysics Data System (ADS)

Styron, R. H.; Hetland, E. A.

2014-12-01

Stress is a first-order control on the deformation state of the earth. However, stress is notoriously hard to measure, and researchers typically only estimate the directions and relative magnitudes of principal stresses, with little quantification of the uncertainties or absolute magnitude. To improve upon this, we have developed methods to constrain the full stress tensor field in a region surrounding a fault, including tectonic, topographic, and lithostatic components, as well as static friction and pore fluid pressure on the fault. Our methods are based on elastic halfspace techniques for estimating topographic stresses from a DEM, and we use a Bayesian approach to estimate accumulated tectonic stress, fluid pressure, and friction from fault geometry and slip rake, assuming Mohr-Coulomb fault mechanics. The nature of the tectonic stress inversion is such that either the stress maximum or minimum is better constrained, depending on the topography and fault deformation style. Our results from the 2008 Wenchuan event yield shear stresses from topography up to 20 MPa (normal-sinistral shear sense) and topographic normal stresses up to 80 MPa on the faults; tectonic stress had to be large enough to overcome topography to produce the observed reverse-dextral slip. Maximum tectonic stress is constrained to be >0.3 * lithostatic stress (depth-increasing), with a most likely value around 0.8, trending 90-110°E. Minimum tectonic stress is about half of maximum. Static fault friction is constrained at 0.1-0.4, and fluid pressure at 0-0.6 * total pressure on the fault. Additionally, the patterns of topographic stress and slip suggest that topographic normal stress may limit fault slip once failure has occurred. Preliminary results from the 2013 Balochistan earthquake are similar, but yield stronger constraints on the upper limits of maximum tectonic stress, as well as tight constraints on the magnitude of minimum tectonic stress and stress orientation. Work in progress on the Wasatch fault suggests that maximum tectonic stress may also be able to be constrained, and that some of the shallow rupture segmentation may be due in part to localized topographic loading. Future directions of this work include regions where high relief influences fault kinematics (such as Tibet).

Continental deformation accommodated by non-rigid passive bookshelf faulting: An example from the Cenozoic tectonic development of northern Tibet

NASA Astrophysics Data System (ADS)

Zuza, Andrew V.; Yin, An

2016-05-01

Collision-induced continental deformation commonly involves complex interactions between strike-slip faulting and off-fault deformation, yet this relationship has rarely been quantified. In northern Tibet, Cenozoic deformation is expressed by the development of the > 1000-km-long east-striking left-slip Kunlun, Qinling, and Haiyuan faults. Each have a maximum slip in the central fault segment exceeding 10s to ~ 100 km but a much smaller slip magnitude (~< 10% of the maximum slip) at their terminations. The along-strike variation of fault offsets and pervasive off-fault deformation create a strain pattern that departs from the expectations of the classic plate-like rigid-body motion and flow-like distributed deformation end-member models for continental tectonics. Here we propose a non-rigid bookshelf-fault model for the Cenozoic tectonic development of northern Tibet. Our model, quantitatively relating discrete left-slip faulting to distributed off-fault deformation during regional clockwise rotation, explains several puzzling features, including the: (1) clockwise rotation of east-striking left-slip faults against the northeast-striking left-slip Altyn Tagh fault along the northwestern margin of the Tibetan Plateau, (2) alternating fault-parallel extension and shortening in the off-fault regions, and (3) eastward-tapering map-view geometries of the Qimen Tagh, Qaidam, and Qilian Shan thrust belts that link with the three major left-slip faults in northern Tibet. We refer to this specific non-rigid bookshelf-fault system as a passive bookshelf-fault system because the rotating bookshelf panels are detached from the rigid bounding domains. As a consequence, the wallrock of the strike-slip faults deforms to accommodate both the clockwise rotation of the left-slip faults and off-fault strain that arises at the fault ends. An important implication of our model is that the style and magnitude of Cenozoic deformation in northern Tibet vary considerably in the east-west direction. Thus, any single north-south cross section and its kinematic reconstruction through the region do not properly quantify the complex deformational processes of plateau formation.

Fault geometric complexity and how it may cause temporal slip-rate variation within an interacting fault system

NASA Astrophysics Data System (ADS)

Zielke, Olaf; Arrowsmith, Ramon

2010-05-01

Slip-rates along individual faults may differ as a function of measurement time scale. Short-term slip-rates may be higher than the long term rate and vice versa. For example, vertical slip-rates along the Wasatch Fault, Utah are 1.7+/-0.5 mm/yr since 6ka, <0.6 mm/yr since 130ka, and 0.5-0.7 mm/yr since 10Ma (Friedrich et al., 2003). Following conventional earthquake recurrence models like the characteristic earthquake model, this observation implies that the driving strain accumulation rates may have changed over the respective time scales as well. While potential explanations for such slip-rate variations may be found for example in the reorganization of plate tectonic motion or mantle flow dynamics, causing changes in the crustal velocity field over long spatial wavelengths, no single geophysical explanation exists. Temporal changes in earthquake rate (i.e., event clustering) due to elastic interactions within a complex fault system may present an alternative explanation that requires neither variations in strain accumulation rate or nor changes in fault constitutive behavior for frictional sliding. In the presented study, we explore this scenario and investigate how fault geometric complexity, fault segmentation and fault (segment) interaction affect the seismic behavior and slip-rate along individual faults while keeping tectonic stressing-rate and frictional behavior constant in time. For that, we used FIMozFric--a physics-based numerical earthquake simulator, based on Okada's (1992) formulations for internal displacements and strains due to shear and tensile faults in a half-space. Faults are divided into a large number of equal-sized fault patches which communicate via elastic interaction, allowing implementation of geometrically complex, non-planar faults. Each patch has assigned a static and dynamic friction coefficient. The difference between those values is a function of depth--corresponding to the temperature-dependence of velocity-weakening that is observed in laboratory friction experiments and expressed in an [a-b] term in Rate-State-Friction (RSF) theory. Patches in the seismic zone are incrementally loaded during the interseismic phase. An earthquake initiates if shear stress along at least one (seismic) patch exceeds its static frictional strength and may grow in size due to elastic interaction with other fault patches (static stress transfer). Aside from investigating slip-rate variations due to the elastic interactions within a fault system with this tool, we want to show how such modeling results can be very useful in exploring the physics underlying the patterns that the paleoseismology sees and that those methods (simulation and observations) can be merged, with both making important contributions. Using FIMozFric, we generated synthetic seismic records for a large number of fault geometries and structural scenarios to investigate along-fault slip accumulation patterns and the variability of slip at a point. Our simulations show that fault geometric complexity and the accompanied fault interactions and multi-fault ruptures may cause temporal deviations from the average fault slip-rate, in other words phases of earthquake clustering or relative quiescence. Slip-rates along faults within an interacting fault system may change even when the loading function (stressing rate) remains constant and the magnitude of slip rate change is suggested to be proportional to the magnitude of fault interaction. Thus, spatially isolated and structurally mature faults are expected to experience less slip-rate changes than strongly interacting and less mature faults. The magnitude of slip-rate change may serve as a proxy for the magnitude of fault interaction and vice versa.

Slow slip event at Kilauea Volcano

USGS Publications Warehouse

Poland, Michael P.; Miklius, Asta; Wilson, J. David; Okubo, Paul G.; Montgomery-Brown, Emily; Segall, Paul; Brooks, Benjamin; Foster, James; Wolfe, Cecily; Syracuse, Ellen; Thurbe, Clifford

2010-01-01

Early in the morning of 1 February 2010 (UTC; early afternoon 31 January 2010 local time), continuous Global Positioning System (GPS) and tilt instruments detected a slow slip event (SSE) on the south flank of Kilauea volcano, Hawaii. The SSE lasted at least 36 hours and resulted in a maximum of about 3 centimeters of seaward displacement. About 10 hours after the start of the slip, a flurry of small earthquakes began (Figure 1) in an area of the south flank recognized as having been seismically active during past SSEs [Wolfe et al., 2007], suggesting that the February earthquakes were triggered by stress associated with slip [Segall et al., 2006].

Bayesian explorations of fault slip evolution over the earthquake cycle

NASA Astrophysics Data System (ADS)

Duputel, Z.; Jolivet, R.; Benoit, A.; Gombert, B.

2017-12-01

The ever-increasing amount of geophysical data continuously opens new perspectives on fundamental aspects of the seismogenic behavior of active faults. In this context, the recent fleet of SAR satellites including Sentinel-1 and COSMO-SkyMED permits the use of InSAR for time-dependent slip modeling with unprecedented resolution in time and space. However, existing time-dependent slip models rely on spatial smoothing regularization schemes, which can produce unrealistically smooth slip distributions. In addition, these models usually do not include uncertainty estimates thereby reducing the utility of such estimates. Here, we develop an entirely new approach to derive probabilistic time-dependent slip models. This Markov-Chain Monte Carlo method involves a series of transitional steps to predict and update posterior Probability Density Functions (PDFs) of slip as a function of time. We assess the viability of our approach using various slow-slip event scenarios. Using a dense set of SAR images, we also use this method to quantify the spatial distribution and temporal evolution of slip along a creeping segment of the North Anatolian Fault. This allows us to track a shallow aseismic slip transient lasting for about a month with a maximum slip of about 2 cm.

Present-Day Strain Transfer Across the Yakutat Collision in SW Yukon - SE Alaska: The Death of the Southern Denali Fault?

NASA Astrophysics Data System (ADS)

Marechal, A.; Mazzotti, S.; Ritz, J. F.; Ferry, M. A.; Freymueller, J. T.

2014-12-01

In SW Yukon-SE Alaska, the present-day Pacific-North America relative motion is highly oblique to the main plate boundary, resulting in strong strain-partitioning tectonics that link the Aleutian subduction to the west to Queen Charlotte transform to the south. This transition region is also the site of present-day orogeny and accretion of the Yakutat Terrane to the Northern Cordillera. Multiple datasets (GPS, geomorphology, seismicity) are integrated to characterize and quantify strain patterns, with particular emphasis on strain partitioning between strike-slip and shortening deformation. New GPS data straddling the main faults (Denali, Totschunda, Fairweather) indicate that, south of the collision corner, 95% of the Pacific-North America strike-slip motion is accommodated on the plate-boundary Fairweather Fault, leaving near-zero motion on the Denali Fault only ~100 km inboard. In contrast, the fault-perpendicular component is strongly distributed between shortening offshore, in the orogen, and inland outward motion. In the region of highest convergence obliquity, GPS data show a diffuse indentor-like deformation, with strong along-strike variations of the main fault slip rates. Preliminary results of a regional geomorphology study give further information about the Denali Fault, where previous data suggest a velocity decrease from 8 mm/yr (Matmon et al.,2006) to 4 mm/yr (Seitz et al., 2010). A high resolution DEM processed from Pleiades satellite imagery highlights a significant vertical component on the Denali Fault and very little to no strike-slip movement in its southern part. Metric-scale displacements are measured along the "inactive" part of the fault showing recent vertical deformation since the Last Glacial Maximum (~20 kyrs ago). In contrast, significant dextral offsets on post-LGM structures are measured on the southern Totschunda Fault. Ongoing datation of geomorphological markers (Be10, OSL) will give us new slip-rate estimates along the southern part of the main transpressional faults (Denali, Totschunda). Our preliminary results suggest that, both south and north of the collision front, the lithospheric scale Denali Fault does not show any significant strike slip movement and that deformation is mostly accommodated along the Fairweather and Totschunda Faults.

Seismic slip on clay nano-foliation

NASA Astrophysics Data System (ADS)

Aretusini, S.; Pluemper, O.; Passelègue, F. X.; Spagnuolo, E.; Di Toro, G.

2017-12-01

Deformation processes active at seismic slip rates (ca. 1 m/s) on smectite-rich slipping zones are not well understood, although they likely control the mechanical behaviour of: i) subduction zone faults affected by tsunamigenic earthquakes (e.g. Japan Trench affected by Tohoku-Oki 2011 earthquake), ii) plate-boundary faults (e.g. San Andreas Fault), and iii) landslide decollements (e.g. 1963 Vajont landslide). Here we present a set of rotary experiments performed on water-dampened 2 mm thick clay-rich (70% wt. smectite and 30% wt. opal) gouge layers sheared at slip rates V ranging from 0.01 to 1.3 m/s, for 3 m of displacement under 5 MPa normal stress. Microstructural analyses were conducted on pre- and post-sheared gouges using focused ion beam scanning electron and transmission electron microscopy. All sheared gouges were slip weakening in the first 0.1 m of displacement, with friction coefficient decreasing from 0.3-0.45 to 0.5-0.15. Then, with progressive slip, gouges evolved to slip-strengthening (final friction coefficient of 0.35-0.48) at V ≤0.1 m/s and slip-neutral (final friction of 0.05) at V=1.3 m/s. Despite the large difference in the imposed slip rate and frictional behaviour, the slipping zone always consisted of a nano-foliation defined by sub-micrometric smectite crystals wrapping opal grains. The nano-foliated layer thickness decreased from 1.5 mm at V≤0.1 m/s to 0.15 mm at V=1.3 m/s. The presence of a similar nano-foliation in all the smectite-rich wet gouges suggests the activation of similar deformation processes, dominated by frictional slip on grain boundary and basal planes. The variation of deformed thickness with slip rate shows that dynamic weakening, occurring only at seismic slip rates, is controlled by strain localization.

Slip-deficit rate distribution along the Nankai trough, southwest Japan, with elastic lithosphere and viscoelastic asthenosphere

NASA Astrophysics Data System (ADS)

Noda, A.; Saito, T.; Fukuyama, E.

2017-12-01

In southwest Japan, great thrust earthquakes occurred on the plate interface along the Nankai trough with a recurrence time of about 100 yr. Most studies estimated slip deficits on the seismogenic zone from interseismic GNSS velocity data assuming elastic slip-response functions (e.g. Loveless and Meade, 2016; Yokota et al., 2016). The observed surface velocities, however, include effects of viscoelastic relaxation in the asthenosphere caused by slip history of seismic cycles on the plate interface. Following Noda et al. (2013, GJI), the interseismic surface velocities due to seismic cycle can be represented by the superposition of (1) completely relaxed viscoelastic response to steady slip rate over the whole plate interface, (2) completely relaxed viscoelastic response to steady slip deficit rate in the seismogenic zone, and (3) surface velocity due to viscoelastic stress relaxation after the last interplate earthquake. Subtracting calculated velocities due to steady slip (1) from velocity data observed after the postseismic stress relaxation (3) decays sufficiently, we can formulate an inverse problem of estimating slip deficit rates from the residual velocities using completely relaxed slip-response functions. In an elastic (lithosphere) - viscoelastic (asthenosphere) layered half-space, the completely relaxed responses do not depend on the viscosity of asthenosphere, but depend on the thickness of lithosphere. In this study, we investigate the effects of structure model on the estimation of slip deficit rate distribution. First, we analyze GNSS daily coordinate data (GEONET F3 Solution, GSI), and obtain surface velocity data for overlapped periods of 6 yr (1996-2002, 1999-2005, 2002-2008, 2005-2011). There is no significant temporal change in the velocity data, which suggests that postseismic stress relaxations after the 1944 Tonankai and the 1946 Nankai earthquakes decayed sufficiently. Next, we estimate slip deficit rate distribution from velocity data from 2005 to 2011 together with seafloor geodetic data (Yokota et al., 2016). There is a significant difference between the results using elastic and completely relaxed responses. While the result using elastic responses shows high slip-deficit rate zone in coastal regions, they are located trenchward if using completely relaxed responses.

Slow-slip events on the Whillans Ice Plain, Antarctica, described using rate-and-state friction as an ice stream sliding law

NASA Astrophysics Data System (ADS)

Lipovsky, Bradley Paul; Dunham, Eric M.

2017-04-01

The Whillans Ice Plain (WIP), Antarctica, experiences twice daily tidally modulated stick-slip cycles. Slip events last about 30 min, have sliding velocities as high as ˜0.5 mm/s (15 km/yr), and have total slip ˜0.5 m. Slip events tend to occur during falling ocean tide: just after high tide and just before low tide. To reproduce these characteristics, we use rate-and-state friction, which is commonly used to simulate tectonic faulting, as an ice stream sliding law. This framework describes the evolving strength of the ice-bed interface throughout stick-slip cycles. We present simulations that resolve the cross-stream dimension using a depth-integrated treatment of an elastic ice layer loaded by tides and steady ice inflow. Steady sliding with rate-weakening friction is conditionally stable with steady sliding occurring for sufficiently narrow ice streams relative to a nucleation length. Stick-slip cycles occur when the ice stream is wider than the nucleation length or, equivalently, when effective pressures exceed a critical value. Ice streams barely wider than the nucleation length experience slow-slip events, and our simulations suggest that the WIP is in this slow-slip regime. Slip events on the WIP show a sense of propagation, and we reproduce this behavior by introducing a rate-strengthening region in the center of the otherwise rate-weakening ice stream. If pore pressures are raised above a critical value, our simulations predict that the WIP would exhibit quasi-steady tidally modulated sliding as observed on other ice streams. This study validates rate-and-state friction as a sliding law to describe ice stream sliding styles.

Limit on slip rate and timing of recent seismic ground-ruptures on the Jinghong fault, SE of the eastern Himalayan syntaxis

NASA Astrophysics Data System (ADS)

Shi, Xuhua; Weldon, Ray; Liu-Zeng, Jing; Wang, Yu; Weldon, Elise; Sieh, Kerry; Li, Zhigang; Zhang, Jinyu; Yao, Wenqian; Li, Zhanfei

2018-06-01

Quantifying slip rates and earthquake occurrence of active faults on the Shan Plateau, southeast of the eastern Himalayan syntaxis, is critical to assessing the seismic hazard and understanding the kinematics and geodynamics of this region. Most previous estimates of slip rates are averaged over either many millions of years using offset geological markers or decades using GPS. Well-constrained millennial slip rates of these faults remain sparse and constraints on recurrence rates of damaging earthquakes exist only for a few faults. Here we investigate the millennial slip rate and timing of recent earthquakes on the Jinghong fault, one of the geomorphically most significant sinistral-slip faults on the central Shan Plateau. We map and reconstruct fault offset (18 ± 5 m) of alluvial fan features at Manpa on the central Jinghong fault, using a 0.1 m-resolution digital surface model obtained from an unmanned aerial vehicle survey. We establish a slip rate, ≤2.5 ± 0.7 mm/yr over the past 7000 years, using pit-exposed stratigraphy. This millennial slip rate is consistent with rates averaged over both decadal and million-year timescales. Excavations at three sites near the town of Gelanghe on the northeastern Jinghong fault demonstrate 1) that the last seismic ground-rupture occurred between 482 and 889 cal yr BP, most likely in the narrower window 824-767 cal yr BP, if the lack of large earthquakes in the historical earthquake record is reliable, and 2) that multiple fault ruptures have occurred since 3618 cal yr BP. Combining this finding with a lack of large earthquakes in the 800-year-long Chinese historic record in this region, we suggest an average recurrence interval of seismic ground-ruptures on the order of 1000 years. This recurrence interval is consistent with the slip rate of the Jinghong fault and the size and earthquake frequency on other sinistral faults on the Shan Plateau.

Fabrication of hydroxyapatite ceramics with controlled pore characteristics by slip casting.

PubMed

Yao, Xiumin; Tan, Shouhong; Jiang, Dongliang

2005-02-01

Porous hydroxyapatite (HAp) ceramics with controlled pore characteristics were fabricated using slip casting method by mixing PMMA with HAp powder. The optimum conditions of HAp slip for slip casting was achieved by employing various experimental techniques, zeta potential and sedimentation, as a function of pH of the slips in the pH range of 4-12. HAp suspensions displayed an absolute maximum in zeta potential values and a minimum in sedimentation height at pH 11.5. The optimal amount of dispersant for the HAp suspensions was found at 1.0 wt% according to the viscosity of 25 vol% HAp slurry. The rheological behaviour of HAp slurry displays a shear-thinning behavior without thixotropy, which is needed in slip casting processing. The pore characteristics of sintered porous hydroxyapatite bioceramics can be controlled by added PMMA particle size and volume. The obtained ceramics exhibit higher strength than those obtained by dry pressing.

Temporal slip rate variability in the Lower Rhine Embayment, Northwest Europe

NASA Astrophysics Data System (ADS)

Gold, Ryan; Kuebler, Simon; Friedrich, Anke

2016-04-01

Low strain regions may be characterized by long periods of seismic quiescence, punctuated by periods of clustered earthquake activity. This type of non-periodic recurrence behavior challenges accurate seismic hazard analysis. The Lower Rhine Embayment in the German-Belgium-Netherland border region presents a unique opportunity to characterize the long-term record of faulting to evaluate the periodicity of earthquake occurrence in a low strain region. The Lower Rhine Embayment is covered by a high-resolution record of Quaternary terraces associated with the Rhine and Maas (Meuse) Rivers and their tributaries. These terraces are cut by numerous NW-trending faults and record cumulative displacements that exceed 100 m in numerous locations. In this study, we exploit this rich record of faulted fluvial terraces and find convincing evidence for temporally varying rates of Quaternary fault movement across the Lower Rhine Embayment. First, we document a significant increase in vertical fault slip rates since 700 ka, compared to the average slip rate since the start of the Quaternary using the top and base of the Main Terrace, respectively. Increases in slip rate exceed 500% along many of the faults, including the Swist/Erft, Stockheim, Viersen, Sandgewand, and Kirspenich fault systems. This increase in fault slip rate corresponds to a regional period of increased tectonic uplift of the Rhenish Massif, increased volcanism in Eifel, and incision of the Rhine River. In a second and related analysis, we synthesize terrace offset and age information from the Feldbiss fault system along the western boundary of the Lower Rhine Embayment, which transects a flight of Quaternary terraces associated with the Mass river. This analysis reveals evidence for secular variation in slip rate. In particular, we identify two periods of higher slip rate (800-400 ka and 130-100 ka), where fault slip rate exceeds the longer-term average slip rate of 0.04-0.05 mm/yr by as much as a factor of two. These results show that in the Lower Rhine Embayment low-strain region, the tempo of strain release (and therefore earthquakes) is non-steady. This variable slip behavior should be incorporated into future efforts to characterize seismic hazard across the region.

Horizontal slip along Alleghanian joints of the Appalachian plateau: evidence showing that mild penetrative strain does little to change the pristine appearance of early joints

NASA Astrophysics Data System (ADS)

Engelder, Terry; Haith, Benjamin F.; Younes, Amgad

2001-07-01

Some Alleghanian joints in black shales of the Geneseo and Middlesex Formations of the Catskill Delta complex, Finger Lakes district, New York, slipped horizontally up to 8 cm. Horizontal slip is measured by the offset of ENE-striking joints. Alleghanian joints striking 330-350° display a right-lateral slip with an average value of 1.9 cm, while joints striking 004-010° slip in the left-lateral sense with an average value of 1.3 cm. The maximum horizontal stress (SH) driving this slip falls between 350° and 004°, the orientation of local Alleghanian layer-parallel shortening as indicated by both disjunctive and pencil cleavage. By commonality of orientation, we infer that slip on Alleghanian joints is driven contemporaneously with layer-parallel shortening. If so, the offset ENE-striking joints predate the Alleghanian stress field. These observations mean that both pre-Alleghanian and early Alleghanian joints persist through a period of penetrative strain.

Pre-, Co-, and Post-Seismic Fault Slip in the Northern Chile Seismic Gap Associated with the April 1, 2014 (Mw 8.2) Pisagua Earthquake.

NASA Astrophysics Data System (ADS)

Simons, M.; Duputel, Z.; Fielding, E. J.; Galetzka, J.; Genrich, J. F.; Jiang, J.; Jolivet, R.; Kanamori, H.; Moore, A. W.; Ortega Culaciati, F. H.; Owen, S. E.; Riel, B. V.; Rivera, L. A.; Carrizo, D.; Cotte, N.; Jara, J.; Klotz, J.; Norabuena, E. O.; Ortega, I.; Socquet, A.; Samsonov, S. V.; Valderas Bermejo, M.

2014-12-01

The April 1, 2014 (Mw 8.2) Pisagua Earthquake occurred in Northern Chile, within a long recognized seismic gap in the Central Andean region that last experienced major megathrust events in 1868 and 1877. We built a continuous GPS network starting in 2005, with the ultimate goal of understanding the kinematics and dynamics of this portion of the subduction zone. Using observations from this network, as well as others in the region, combined with InSAR, seismic and tsunami observations, we obtain estimates of inter-seismic, co-seismic and initial post-seismic fault slip using an internally consistent Bayesian unregularized approach. We evaluate the extent of spatial overlap between regions of fault slip during this different time periods. Of particular interest to this event is the extent and nature of any geodetic evidence for transient slow fault slip preceding the Pisagua Earthquake mainshock. To this end, we compare daily and high rate GPS solutions, the former of which shows long period transient motion started about 15 days before the mainshock and with maximum registered amplitude of 14.2 +/- 2 [mm] at site PSGA. Contrary to published findings, we find that pre-seismic deformation seen by the GPS network can be explained as coseismic motion associated with the multiple foreshocks.

Spontaneous Aseismic and Seismic Slip Transients on Evolving Faults Simulated in a Continuum-Mechanics Framework

NASA Astrophysics Data System (ADS)

Herrendoerfer, R.; Gerya, T.; van Dinther, Y.

2016-12-01

The convergent plate motion in subduction zones is accommodated by different slip modes: potentially dangerous seismic slip and imperceptible, but instrumentally detectable slow slip transients or steady slip. Despite an increasing number of observations and insights from laboratory experiments, it remains enigmatic which local on- and off-fault conditions favour slip modes of different source characteristics (i.e., slip velocity, duration, seismic moment). Therefore, we are working towards a numerical model that is able to simulate different slip modes in a consistent way with the long-term evolution of the fault system. We extended our 2D, continuum mechanics-based, visco-elasto-plastic seismo-thermo-mechanical (STM) model, which simulated cycles of earthquake-like ruptures, albeit only at plate tectonic slip rates (van Dinther et al, JGR, 2013). To model a wider slip spectrum including seismic slip rates, we, besides improving the general numerical approach, implemented an invariant reformulation of the conventional rate-and state dependent friction (RSF) and an adaptive time-stepping scheme (Lapusta and Rice, JGR, 2001). In a simple setup with predominantly elastic plates that are juxtaposed along a predefined fault of certain width, we vary the characteristic slip distance, the mean normal stress and the size of the rate-weakening zone. We show that the resulting stability transitions from decaying oscillations, periodic slow slip, complex periodic to seismic slip agree with those of conventional RSF seismic cycle simulations (e.g. Liu and Rice, JGR, 2007). Additionally, we will present results of the investigation concerning the effect of the fault width and geometry on the generation of different slip modes. Ultimately, instead of predefining a fault, we simulate the spatio-temporal evolution of a complex fault system that is consistent with the plate motions and rheology. For simplicity, we parametrize the fault development through linear slip-weakening of cohesion and apply RSF friction only in cohesionless material. We report preliminary results of the interaction between slip modes and the fault growth during different fault evolution stages.

The Evolution of the Seismic-Aseismic Transition During the Earthquake Cycle: Constraints from the Time-Dependent Depth Distribution of Aftershocks

NASA Astrophysics Data System (ADS)

Rolandone, F.; Bürgmann, R.; Nadeau, R.; Freed, A.

2003-12-01

We have demonstrated that in the aftermath of large earthquakes, the depth extent of aftershocks shows an immediate deepening from pre-earthquake levels, followed by a time-dependent postseismic shallowing. We use these seismic data to constrain the variation of the depth of the seismic-aseismic transition with time throughout the earthquake cycle. Most studies of the seismic-aseismic transition have focussed on the effect of temperature and/or lithology on the transition either from brittle faulting to viscous flow or from unstable to stable sliding. They have shown that the maximum depth of seismic activity is well correlated with the spatial variations of these two parameters. However, little has been done to examine how the maximum depth of seismogenic faulting varies locally, at the scale of a fault segment, during the course of the earthquake cycle. Geologic and laboratory observations indicate that the depth of the seismic-aseismic transition should vary with strain rate and thus change with time throughout the earthquake cycle. We quantify the time-dependent variations in the depth of seismicity on various strike-slip faults in California before and after large earthquakes. We specifically investigate (1) the deepening of the aftershocks relative to the background seismicity, (2) the time constant of the postseismic shallowing of the deepest earthquakes, and (3) the correlation of the time-dependent pattern with the coseismic slip distribution and the expected stress increase. Together with geodetic measurements, these seismological observations form the basis for developing more sophisticated models for the mechanical evolution of strike-slip shear zones during the earthquake cycle. We develop non-linear viscoelastic models, for which the brittle-ductile transition is not fixed, but varies with assumed temperature and calculated stress gradients. We use them to place constraints on strain rate at depth, on time-dependent rheology, and on the partitioning of deformation between brittle faulting and distributed viscous flow associated with the earthquake cycle.

Slow Earthquakes and The Mechanics of Slow Frictional Stick-Slip

NASA Astrophysics Data System (ADS)

Marone, Chris; Scuderi, Marco; Leeman, John; Saffer, Demian; Collettini, Cristiano; Johnson, Paul

2015-04-01

Slow earthquakes represent one mode of the spectrum of fault slip behaviors ranging from steady aseismic slip to normal earthquakes. Like normal earthquakes, slow earthquakes can occur repetitively, such that a fault fails in a form of stick-slip failure defined by interseismic strain accumulation and slow, quasidynamic slip. The mechanics of frictional stick-slip and seismogenic faulting appear to apply to slow earthquakes, however, the mechanisms that limit dynamic slip velocity, rupture propagation speed, and the scaling between moment and duration of slow earthquakes are poorly understood. Here, we describe laboratory experiments that explore the mechanics of repetitive, slow frictional stick-slip failure. We document the role of loading stiffness and friction constitutive behavior in dictating the properties of repetitive, frictional stick-slip. Our results show that a spectrum of dynamic and quasidynamic slip velocities can occur in stick-slip events depending on the relation between loading stiffness k and the rheologic critical stiffness kc given, in the context of rate and state friction, by the ratio of the friction rate parameter (b-a) divided by the critical friction distance Dc. Slow slip is favored by conditions for which k is ~ equal to kc, whereas normal, fast stick slip occurs when k/kc < 1. We explore the role of elastic coupling and spatially extended slip propagation by comparing slow slip results for shear in a layer driven by forcing blocks of varying stiffness. We evaluate our data in the framework of rate and state friction laws and focus on the frictional mechanics of slow stick-slip failure with special attention paid to the connections between quasidynamic failure and mechanisms of the brittle-ductile transition in fault rocks.

Late Quaternary activity of the Ecemiş Fault Zone, Turkey; implications from cosmogenic 36Cl dating of offset alluvial fans

NASA Astrophysics Data System (ADS)

Akif Sarıkaya, Mehmet; Yıldırım, Cengiz; Çiner, Attila

2014-05-01

The Ecemiş Fault Zone is the southernmost segment of the Central Anatolian Fault Zone. The tectonic trough of the fault zone defines the boundary between the Central and Eastern Taurides Ranges. The presence of faulted alluvial fans and colluvium within this trough provide favorable conditions to unravel the Late Quaternary slip-rate of the fault zone by cosmogenic surface exposure dating. In this context, we focused on the main strand of the fault zone and also on the Cevizlik Fault that delimits the mountain front of the Aladaǧlar, Eastern Taurides. Geomorphic mapping and topographic surveying indicate four different alluvial fan levels deposited along the main strand. Our topographic survey reveals 60±5 m horizontal and 18±2 m vertical displacement of the oldest fan surface (AF1) associated with the main strand of the fault zone. We dated the surface of the AF1 with 13 cosmogenic 36Cl samples. Our results indicate that the AF1 surface was abandoned maximum 105.3±1.5 ka ago. Accordingly, we propose 0.57±0.05 mm/yr horizontal and 0.17±0.02 mm/yr vertical mean slip-rates since 100 ka for the main strand. On the other hand, we measured 20±2 m vertical displacement on the colluvium along the Cevizlik Fault. The surface exposure age of the colluvium yielded 21.9±0.3 ka that translates to 0.91±0.09 mm/yr vertical slip-rate for the Cevizlik Fault. Our results reveal significant Quaternary deformation, and low strain rates might indicate very long earthquake recurrence intervals along the fault zone.

Evidence for Recent Activity on the Chatham Strait Fault from Seismic Reflection and GPS Modeling, Southeastern Alaska

NASA Astrophysics Data System (ADS)

Conrad, J. E.; Brothers, D. S.; Elliott, J.; Haeussler, P. J.

2016-12-01

Chatham Strait and its northern extension, Lynn Canal, form the southern end of the Denali fault system, which arcs across southern Alaska and the Yukon Territory. Paleozoic rocks are offset by 180 km across Chatham Strait, confirming a history of significant dextral faulting. Tertiary volcanic rocks on either side of the fault, dated on one side at 28 Ma, have been interpreted as a piercing point indicating post-Oligocene movement. Historical seismic activity is low along the length of Chatham Strait fault (CSF), but the prominent geomorphological expression of the CSF continues to invite the idea that the fault is active and carries some component of modern plate motion, linking to the Eastern Denali fault at the northern end of Lynn Canal. In 2015, the USGS collected high-frequency chirp and multichannel seismic (MCS) reflection profiles in Lynn Canal, in order to image evidence of deformation related to offset along the CSF. During the Last Glacial Maximum, Lynn Canal was completely filled with ice, which mostly removed older sediments and left an irregular but freshly scraped bedrock surface upon deglaciation. MCS profiles image a sequence of younger onlapping sediments that thicken from about 150 m in the north part of the study area to over 250 m in the south. These sediments record the transition from an initial outwash phase with rapid deposition during early stages of deglaciation to deposition in current open-water conditions in depths of 275-325 m that span the last 12,000-14,000 years. Seismic reflection profiles show only minor and localized faulting in these sediments, and there is no evidence of any continuous deformation along the axis of Lynn Canal that would suggest significant offset along the CSF. Fault models constrained by GPS data allow, but do not require, a maximum slip rate of about 2-3 mm/yr along the CSF; higher slip rates on the CSF result in significant misfit to GPS data in the surrounding region. Overall, our results suggest that slip rates may be <1 mm/yr, and it is plausible that the CSF has no current activity.

Mirror-like slip surfaces in dolostone: natural and experimental constraints on a potential seismic marker

NASA Astrophysics Data System (ADS)

Fondriest, M.; Smith, S. A.; Di Toro, G.; Nielsen, S. B.

2012-12-01

The lack of clear geological markers of seismic faulting represents a major limitation in our current comprehension of earthquake physics. At present pseudotachylytes (i.e. friction-induced melts) are the only unambiguously identified indicator of ancient seismicity in exhumed fault zones, but pseudotachylytes are not found in many rock types, including carbonates. We report the occurrence of small-displacement, mirror-like slip surfaces from a fault zone cutting dolostones. A combination of field observations and rotary shear friction experiments suggests that such slip surfaces: 1) are formed only at seismic slip rates, and 2) could potentially be used to estimate power dissipation during individual slip events. The Foiana Line (FL) is a major NNE-SSW-trending sinistral transpressive fault in the Italian Southern Alps. The outcropping fault zone consists of a <300 m wide zone of heavily fractured ("pulverized") dolostones cut by a network of mirror-like slip surfaces. The slip surfaces have displacements ranging between 0.04 m and 0.5 m and their mirror-like appearance indicates that the wavelength of surface roughness is <1 μm. The slip surfaces have mainly dip-slip reverse kinematics and were exhumed from ~2 km depth. Resolved normal stress on the slip surfaces is estimated in the range 30-50 MPa. To understand how the mirror-like slip surfaces may have developed, slow- to high-velocity rotary-shear experiments using SHIVA (INGV, Rome) were performed on 3 mm thick layers of dolomite gouge (grain size <250 μm) collected from the FL. Tests were conducted using a purpose-built gouge sample holder at slip rates of 0.0001-1.13 m/s, normal stresses up to 26 MPa and displacements in the range 0.02-3.5 m. At seismic slip rates of 1.13 m/s the dolomite gouge shows a dramatic reduction of the friction coefficient (μ) from a peak value of ~0.7 to a steady-state value of ~0.25. The gouge starts to weaken above a threshold velocity in the range 0.19-0.49 m/s following a transient phase of strengthening. During the tests the instantaneous power density (shear stress*slip rate) dissipated on the sample reaches values of 6-10 MW/m2 over distances of 0.02-1 m, comparable to those of natural earthquakes. At 26 MPa normal stress a mirror-like slip surface is formed after only 0.03 m of slip. At intermediate slip rates (0.113 m/s) only moderate reductions in μ are observed. Instantaneous power density is ~1 MW/m2 and the mirror-like slip surface starts to develop after 0.1 m of slip. At sub-seismic slip rates (0.0001-0.0013 m/s) μ remains ~0.7, instantaneous power density is ~0.02 MW/m2, and no mirror-like slip surface develops. Microstructural observations suggest that the natural and experimental slip zones are comparable: both have a compacted layer up to 20 μm thick immediately below the mirror-like slip surface in which deformation is strongly localized. The layer consists of partially-welded dolomite clasts 0.1-10 μm in size. In the experimental samples, chemical analyses recognized small (<100 μm long), discontinuous patches of periclase and Mg-calcite nanoparticles formed by dolomite decomposition. Field, experimental and microstructural data suggest that mirror-like slip surfaces in dolostone develop at seismic conditions, when instantaneous power density is of the order of 1-10 MW/m2.

Fault connectivity, distributed shortening, and impacts on geologic- geodetic slip rate discrepancies in the central Mojave Desert, California

NASA Astrophysics Data System (ADS)

Selander, J.; Oskin, M. E.; Cooke, M. L.; Grette, K.

2015-12-01

Understanding off-fault deformation and distribution of displacement rates associated with disconnected strike-slip faults requires a three-dimensional view of fault geometries. We address problems associated with distributed faulting by studying the Mojave segment of the East California Shear Zone (ECSZ), a region dominated by northwest-directed dextral shear along disconnected northwest- southeast striking faults. We use a combination of cross-sectional interpretations, 3D Boundary Element Method (BEM) models, and slip-rate measurements to test new hypothesized fault connections. We find that reverse faulting acts as an important means of slip transfer between strike-slip faults, and show that the impacts of these structural connections on shortening, uplift, strike-slip rates, and off-fault deformation, help to reconcile the overall strain budget across this portion of the ECSZ. In detail, we focus on the Calico and Blackwater faults, which are hypothesized to together represent the longest linked fault system in the Mojave ECSZ, connected by a restraining step at 35°N. Across this restraining step the system displays a pronounced displacement gradient, where dextral offset decreases from ~11.5 to <2 km from south to north. Cross-section interpretations show that ~40% of this displacement is transferred from the Calico fault to the Harper Lake and Blackwater faults via a set of north-dipping thrust ramps. Late Quaternary dextral slip rates follow a similar pattern, where 1.4 +0.8/-0.4 mm/yr of slip along the Calico fault south of 35°N is distributed to the Harper Lake, Blackwater, and Tin Can Alley faults. BEM model results using revised fault geometries for the Mojave ECSZ show areas of uplift consistent with contractional structures, and fault slip-rates that more closely match geologic data. Overall, revised fault connections and addition of off-fault deformation greatly reduces the discrepancy between geodetic and geologic slip rates.

Biomechanical testing of bioabsorbable cannulated screws for slipped capital femoral epiphysis fixation.

PubMed

Kroeber, Markus W; Rovinsky, David; Haskell, Andrew; Heilmann, Moira; Llotz, Jeff; Otsuka, Norman

2002-06-01

This study compared cannulated 4.5-mm bioabsorbable screws made of self-reinforced poly-levolactic acid to cannulated 4.5-mm steel and titanium screws for resistance to shear stress and ability to generate compression in a polyurethane foam model of slipped capital femoral epiphysis fixation. The maximum shear stress resisted by the three screw types was similar (self-reinforced poly-levolactic acid 371 +/- 146 MPa, steel 442 +/- 43 MPa, and titanium 470 +/- 91 MPa). The maximum compression generated by both the self-reinforced poly-levolactic acid screw (68.5 +/- 3.3 N) and the steel screw (63.3 +/- 5.9 N) was greater than that for the titanium screw (3 +/- 1.4 N, P <.05). These data suggest cannulated self-reinforced poly-levolactic acid screws can be used in the treatment of slipped capital femoral epiphysis because of their sufficient biomechanical strength.

The vertical slip rate of the Sertengshan piedmont fault, Inner Mongolia, China

NASA Astrophysics Data System (ADS)

Zhang, Hao; He, Zhongtai; Ma, Baoqi; Long, Jianyu; Liang, Kuan; Wang, Jinyan

2017-08-01

The vertical slip rate of a normal fault is one of the most important parameters for evaluating its level of activity. The Sertengshan piedmont fault has been studied since the 1980s, but its absolute vertical slip rate has not been determined. In this paper, we calculate the displacements of the fault by measuring the heights of piedmont terraces on the footwall and the stratigraphic depths of marker strata in the hanging wall. We then calculate the vertical slip rate of the fault based on the displacements and ages of the marker strata. We selected nine sites uniformly along the fault to study the vertical slip rates of the fault. The results show that the elevations of terraces T3 and T1 are approximately 1060 m and 1043 m, respectively. The geological boreholes in the basin adjacent to the nine study sites reveal that the elevation of the bottom of the Holocene series is between 1017 and 1035 m and that the elevation of the top of the lacustrine strata is between 925 and 1009 m. The data from the terraces and boreholes also show that the top of the lacustrine strata is approximately 65 ka old. The vertical slip rates are calculated at 0.74-1.81 mm/a since 65 ka and 0.86-2.28 mm/a since the Holocene. The slip rate is the highest along the Wujiahe segment and is lower to the west and east. Based on the findings of a previous study on the fault system along the northern margin of the Hetao graben basin, the vertical slip rates of the Daqingshan and Langshan faults are higher than those of the Sertengshan and Wulashan faults, and the strike-slip rates of these four northern Hetao graben basin faults are low. These results agree with the vertical slip components of the principal stress field on the faults. The results of our analysis indicate that the Langshankou, Wujiahe, and Wubulangkou areas and the eastern end of the Sertengshan fault are at high risk of experiencing earthquakes in the future.

Slip rate and tremor genesis in Cascadia

USGS Publications Warehouse

Wech, Aaron G.; Bartlow, Noel M.

2014-01-01

At many plate boundaries, conditions in the transition zone between seismogenic and stable slip produce slow earthquakes. In the Cascadia subduction zone, these events are consistently observed as slow, aseismic slip on the plate interface accompanied by persistent tectonic tremor. However, not all slow slip at other plate boundaries coincides spatially and temporally with tremor, leaving the physics of tremor genesis poorly understood. Here we analyze seismic, geodetic, and strainmeter data in Cascadia to observe for the first time a large, tremor-generating slow earthquake change from tremor-genic to silent and back again. The tremor falls silent at reduced slip speeds when the migrating slip front pauses as it loads the stronger adjacent fault segment to failure. The finding suggests that rheology and slip-speed-regulated stressing rate control tremor genesis, and the same section of fault can slip both with and without detectable tremor, limiting tremor's use as a proxy for slip.

Earthquake Nucleation on Faults With Heterogeneous Frictional Properties, Normal Stress

NASA Astrophysics Data System (ADS)

Ray, Sohom; Viesca, Robert C.

2017-10-01

We examine the development of an instability of fault slip rate. We consider a slip rate and state dependence of fault frictional strength, in which frictional properties and normal stress are functions of position. We pose the problem for a slip rate distribution that diverges quasi-statically within finite time in a self-similar fashion. Scenarios of property variations are considered and the corresponding self-similar solutions found. We focus on variations of coefficients, a and b, respectively, controlling the magnitude of a direct effect on strength due to instantaneous changes in slip rate and of strength evolution due to changes in a state variable. These results readily extend to variations in fault-normal stress, σ, or the characteristic slip distance for state evolution, Dc. We find that heterogeneous properties lead to a finite number of self-similar solutions, located about critical points of the distributions: maxima, minima, and between them. We examine the stability of these solutions and find that only a subset is asymptotically stable, occurring at just one of the critical point types. Such stability implies that during instability development, slip rate and state evolution can be attracted to develop in the manner of the self-similar solution, which is also confirmed by solutions to initial value problems for slip rate and state. A quasi-static slip rate divergence is ultimately limited by inertia, leading to the nucleation of an outward expanding dynamic rupture: asymptotic stability of self-similar solutions then implies preferential sites for earthquake nucleation, which are determined by distribution of frictional properties.

Steady, modest slip over multiple earthquake cycles on the Owens Valley and Little Lake fault zones

NASA Astrophysics Data System (ADS)

Amos, C. B.; Haddon, E. K.; Burgmann, R.; Zielke, O.; Jayko, A. S.

2015-12-01

A comprehensive picture of current plate-boundary deformation requires integration of short-term geodetic records with longer-term geologic strain. Comparing rates of deformation across these time intervals highlights potential time-dependencies in both geodetic and geologic records and yields critical insight into the earthquake deformation process. The southern Walker Lane Belt in eastern California represents one location where short-term strain recorded by geodesy apparently outpaces longer-term geologic fault slip measured from displaced rocks and landforms. This discrepancy persists both for individual structures and across the width of the deforming zone, where ~1 cm/yr of current dextral shear exceeds Quaternary slip rates summed across individual faults. The Owens Valley and Little Lake fault systems form the western boundary of the southern Walker Lane and host a range of published slip rate estimates from ~1 - 7 mm/yr over varying time intervals based on both geodetic and geologic measurements. New analysis of offset geomorphic piercing lines from airborne lidar and field measurements along the Owens Valley fault provides a snapshot of deformation during individual earthquakes and over many seismic cycles. Viewed in context of previously reported ages from pluvial and other landforms in Owens Valley, these offsets suggest slip rates of ~0.6 - 1.6 mm/yr over the past 103 - 105 years. Such rates agree with similar estimates immediately to the south on the Little Lake fault, where lidar measurements indicate dextral slip averaging ~0.6 - 1.3 mm/yr over comparable time intervals. Taken together, these results suggest steady, modest slip in the absence of significant variations over the Mid-to-Late Quaternary for a ~200 km span of the southwestern Walker Lane. Our findings argue against the presence of long-range fault interactions and slip-rate variations for this portion of the larger, regional fault network. This result also suggests that faster slip-rate estimates from geodetic measurements reflect transients over much shorter time scales. Additionally, the persistence of relatively faster geodetic shear in comparison with time-averaged fault slip leaves open the possibility of significant off-fault deformation or slip on subsidiary structures across the Owens Valley.

A method for mapping apparent stress and energy radiation applied to the 1994 Northridge earthquake fault zone

USGS Publications Warehouse

McGarr, A.; Fletcher, Joe B.

2000-01-01

Using the Northridge earthquake as an example, we demonstrate a new technique able to resolve apparent stress within subfaults of a larger fault plane. From the model of Wald et al. (1996), we estimated apparent stress for each subfault using τa = (G/β)/2 where G is the modulus of rigidity, β is the shear wave speed, and is the average slip rate. The image of apparent stress mapped over the Northridge fault plane supports the idea that the stresses causing fault slip are inhomogeneous, but limited by the strength of the crust. Indeed, over the depth range 5 to 17 km, maximum values of apparent stress for a given depth interval agree with τa(max)=0.06S(z), where S is the laboratory estimate of crustal strength as a function of depth z. The seismic energy from each subfault was estimated from the product τaDA, where A is subfault area and D its slip. Over the fault zone, we found that the radiated energy is quite variable spatially, with more than 50% of the total coming from just 15% of the subfaults.

Modeling of rock friction 2. Simulation of preseismic slip

USGS Publications Warehouse

Dieterich, J.H.

1979-01-01

The constitutive relations developed in the companion paper are used to model detailed observations of preseismic slip and the onset of unstable slip in biaxial laboratory experiments. The simulations employ a deterministic plane strain finite element model to represent the interactions both within the sliding blocks and between the blocks and the loading apparatus. Both experiments and simulations show that preseismic slip is controlled by initial inhomogeneity of shear stress along the sliding surface relative to the frictional strength. As a consequence of the inhomogeneity, stable slip begins at a point on the surface and the area of slip slowly expands as the external loading increases. A previously proposed correlation between accelerating rates of stable slip and growth of the area of slip is supported by the simulations. In the simulations and in the experiments, unstable slip occurs shortly after a propagating slip event traverses the sliding surface and breaks out at the ends of the sample. In the model the breakout of stable slip causes a sudden acceleration of slip rates. Because of velocity dependency of the constitutive relationship for friction, the rapid acceleration of slip causes a decrease in frictional strength. Instability occurs when the frictional strength decreases with displacement at a rate that exceeds the intrinsic unloading characteristics of the sample and test machine. A simple slider-spring model that does not consider preseismic slip appears to approximate the transition adequately from stable sliding to unstable slip as a function of normal stress, machine stiffness, and surface roughness for small samples. However, for large samples and for natural faults the simulations suggest that the simple model may be inaccurate because it does not take into account potentially large preseismic displacements that will alter the friction parameters prior to instability. Copyright ?? 1979 by the American Geophysical Union.

Constraints on the frequency-magnitude relation and maximum magnitudes in the UK from observed seismicity and glacio-isostatic recovery rates

NASA Astrophysics Data System (ADS)

Main, Ian; Irving, Duncan; Musson, Roger; Reading, Anya

1999-05-01

Earthquake populations have recently been shown to have many similarities with critical-point phenomena, with fractal scaling of source sizes (energy or seismic moment) corresponding to the observed Gutenberg-Richter (G-R) frequency-magnitude law holding at low magnitudes. At high magnitudes, the form of the distribution depends on the seismic moment release rate Msolar and the maximum magnitude m_max . The G-R law requires a sharp truncation at an absolute maximum magnitude for finite Msolar. In contrast, the gamma distribution has an exponential tail which allows a soft or `credible' maximum to be determined by negligible contribution to the total seismic moment release. Here we apply both distributions to seismic hazard in the mainland UK and its immediate continental shelf, constrained by a mixture of instrumental, historical and neotectonic data. Tectonic moment release rates for the seismogenic part of the lithosphere are calculated from a flexural-plate model for glacio-isostatic recovery, constrained by vertical deformation rates from tide-gauge and geomorphological data. Earthquake focal mechanisms in the UK show near-vertical strike-slip faulting, with implied directions of maximum compressive stress approximately in the NNW-SSE direction, consistent with the tectonic model. Maximum magnitudes are found to be in the range 6.3-7.5 for the G-R law, or 7.0-8.2 m_L for the gamma distribution, which compare with a maximum observed in the time period of interest of 6.1 m_L . The upper bounds are conservative estimates, based on 100 per cent seismic release of the observed vertical neotectonic deformation. Glacio-isostatic recovery is predominantly an elastic rather than a seismic process, so the true value of m_max is likely to be nearer the lower end of the quoted range.

New geologic slip rates for the Agua Blanca Fault, northern Baja California, Mexico

NASA Astrophysics Data System (ADS)

Gold, P. O.; Behr, W. M.; Fletcher, J. M.; Hinojosa-Corona, A.; Rockwell, T. K.

2015-12-01

Within the southern San Andreas transform plate boundary system, relatively little is known regarding active faulting in northern Baja California, Mexico, or offshore along the Inner Continental Borderland. The inner offshore system appears to be fed from the south by the Agua Blanca Fault (ABF), which strikes northwest across the Peninsular Ranges of northern Baja California. Therefore, the geologic slip rate for the ABF also provides a minimum slip rate estimate for the offshore system, which is connected to the north to faults in the Los Angeles region. Previous studies along the ABF determined slip rates of ~4-6 mm/yr (~10% of relative plate motion). However, these rates relied on imprecise age estimates and offset geomorphic features of a type that require these rates to be interpreted as minima, allowing for the possibility that the slip rate for the ABF may be greater. Although seismically quiescent, the surface trace of the ABF clearly reflects Holocene activity, and given its connectivity with the offshore fault system, more quantitative slip rates for the ABF are needed to better understand earthquake hazard for both US and Mexican coastal populations. Using newly acquired airborne LiDAR, we have mapped primary and secondary fault strands along the segmented western 70 km of the ABF. Minimal development has left the geomorphic record of surface slip remarkably well preserved, and we have identified abundant evidence meter to km scale right-lateral displacement, including new Late Quaternary slip rate sites. We verified potential reconstructions at each site during summer 2015 fieldwork, and selected an initial group of three high potential slip rate sites for detailed mapping and geochronologic analyses. Offset landforms, including fluvial terrace risers, alluvial fans, and incised channel fill deposits, record displacements of ~5-80 m, and based on minimal soil development, none appear older than early Holocene. To quantitatively constrain landform ages, we collected surface and depth profile samples for 10Be cosmogenic exposure dating. We also identified sites for new paleoseismic excavations, and documented evidence of the last two earthquakes, each of which produced ~2.5 m of surface displacement. We expect new Holocene slip rates for the Agua Blanca Fault to be forthcoming in fall of 2015.

Perception of slipperiness and prospective risk of slipping at work

PubMed Central

Courtney, Theodore K; Verma, Santosh K; Chang, Wen-Ruey; Huang, Yueng-Hsiang; Lombardi, David A; Brennan, Melanye J; Perry, Melissa J

2013-01-01

Objectives Falls are a leading cause of injury at work, and slipping is the predominant cause of falling. Prior research has suggested a modest correlation between objective measures (such as coefficient of friction, COF) and subjective measures of slipperiness (such as worker perceptions) in the workplace. However, the degree of association between subjective measures and the actual risk of slipping at the workplace is unknown. This study examined the association between perception of slipperiness and the risk of slipping. Methods 475 workers from 36 limited-service restaurants participated in a 12-week prospective cohort study. At baseline, demographic information was collected, participants rated floor slipperiness in eight areas of the restaurant, and work environment factors, such as COF, were measured. Restaurant-level and area-level mean perceptions of slipperiness were calculated. Participants then reported their slip experience at work on a weekly basis for the next 12 weeks. The associations between perception of slipperiness and the rate of slipping were assessed. Results Adjusting for age, gender, body mass index, education, primary language, mean COF, use of slip-resistant shoes, and restaurant chain, each 1-point increase in mean restaurant-level perception of slipperiness (4-point scale) was associated with a 2.71 times increase in the rate of slipping (95% CI 1.25 to 5.87). Results were similar for area-level perception within the restaurant (rate ratios (RR) 2.92, 95% CI 2.41 to 3.54). Conclusions Perceptions of slipperiness and the subsequent rate of slipping were strongly associated. These findings suggest that safety professionals, risk managers and employers could use aggregated worker perceptions of slipperiness to identify slipping hazards and, potentially, to assess intervention effectiveness. PMID:22935953

Perception of slipperiness and prospective risk of slipping at work.

PubMed

Courtney, Theodore K; Verma, Santosh K; Chang, Wen-Ruey; Huang, Yueng-Hsiang; Lombardi, David A; Brennan, Melanye J; Perry, Melissa J

2013-01-01

Falls are a leading cause of injury at work, and slipping is the predominant cause of falling. Prior research has suggested a modest correlation between objective measures (such as coefficient of friction, COF) and subjective measures of slipperiness (such as worker perceptions) in the workplace. However, the degree of association between subjective measures and the actual risk of slipping at the workplace is unknown. This study examined the association between perception of slipperiness and the risk of slipping. 475 workers from 36 limited-service restaurants participated in a 12-week prospective cohort study. At baseline, demographic information was collected, participants rated floor slipperiness in eight areas of the restaurant, and work environment factors, such as COF, were measured. Restaurant-level and area-level mean perceptions of slipperiness were calculated. Participants then reported their slip experience at work on a weekly basis for the next 12 weeks. The associations between perception of slipperiness and the rate of slipping were assessed. Adjusting for age, gender, body mass index, education, primary language, mean COF, use of slip-resistant shoes, and restaurant chain, each 1-point increase in mean restaurant-level perception of slipperiness (4-point scale) was associated with a 2.71 times increase in the rate of slipping (95% CI 1.25 to 5.87). Results were similar for area-level perception within the restaurant (rate ratios (RR) 2.92, 95% CI 2.41 to 3.54). Perceptions of slipperiness and the subsequent rate of slipping were strongly associated. These findings suggest that safety professionals, risk managers and employers could use aggregated worker perceptions of slipperiness to identify slipping hazards and, potentially, to assess intervention effectiveness.

Effects of asperity contact on stick-slip dynamics

NASA Astrophysics Data System (ADS)

Yamaguchi, Tetsuo

2017-04-01

It is believed that asperity contact plays an important role in fricton, in particular in onset of dynamic slip or stick-slip motions. However, there remains very few studies controling asperities and observing their effects on mascoscopic stick-slip behavior or frictional constitutive laws. Here we perform stick-slip friction experiments between compliant gels with well-controlled asperity shape/size/configurations by molding technique. We find that, as curvature radius of the asperity becomes larger and the normal stress becomes smaller, velocity dependence turns from rate-strengthening to rate-weakening and accordingly, frictional behavior transitions from steady sliding, slow slip to fast slip. In this talk, we discuss the asperity size effects based on microscopic/macroscopic observations as well as a theoretical argument.

Simulating spontaneous aseismic and seismic slip events on evolving faults

NASA Astrophysics Data System (ADS)

Herrendörfer, Robert; van Dinther, Ylona; Pranger, Casper; Gerya, Taras

2017-04-01

Plate motion along tectonic boundaries is accommodated by different slip modes: steady creep, seismic slip and slow slip transients. Due to mainly indirect observations and difficulties to scale results from laboratory experiments to nature, it remains enigmatic which fault conditions favour certain slip modes. Therefore, we are developing a numerical modelling approach that is capable of simulating different slip modes together with the long-term fault evolution in a large-scale tectonic setting. We extend the 2D, continuum mechanics-based, visco-elasto-plastic thermo-mechanical model that was designed to simulate slip transients in large-scale geodynamic simulations (van Dinther et al., JGR, 2013). We improve the numerical approach to accurately treat the non-linear problem of plasticity (see also EGU 2017 abstract by Pranger et al.). To resolve a wide slip rate spectrum on evolving faults, we develop an invariant reformulation of the conventional rate-and-state dependent friction (RSF) and adapt the time step (Lapusta et al., JGR, 2000). A crucial part of this development is a conceptual ductile fault zone model that relates slip rates along discrete planes to the effective macroscopic plastic strain rates in the continuum. We test our implementation first in a simple 2D setup with a single fault zone that has a predefined initial thickness. Results show that deformation localizes in case of steady creep and for very slow slip transients to a bell-shaped strain rate profile across the fault zone, which suggests that a length scale across the fault zone may exist. This continuum length scale would overcome the common mesh-dependency in plasticity simulations and question the conventional treatment of aseismic slip on infinitely thin fault zones. We test the introduction of a diffusion term (similar to the damage description in Lyakhovsky et al., JMPS, 2011) into the state evolution equation and its effect on (de-)localization during faster slip events. We compare the slip spectrum in our simulations to conventional RSF simulations (Liu and Rice, JGR, 2007). We further demonstrate the capability of simulating the evolution of a fault zone and simultaneous occurrence of slip transients. From small random initial distributions of the state variable in an otherwise homogeneous medium, deformation localizes and forms curved zones of reduced states. These spontaneously formed fault zones host slip transients, which in turn contribute to the growth of the fault zone.

Frictional properties of the biogenic oozes from the CRISP drilling project: possible evidence of past slip-to-the-trench

NASA Astrophysics Data System (ADS)

Vannucchi, P.; Spagnuolo, E.; Aretusini, S.; Di Toro, G.; Tsutsumi, A.; Ujiie, K.; Namiki, Y.

2015-12-01

The 2011 Tohoku EQ revealed that co-seismic displacement along the megathrust can reach the deformation front of subduction zones. Since then the global significance of slip-to-the-trench has become an important field of study; hence investigation of past events at other active megathrusts is critical. Offshore SE Costa Rica the deformation front of the Caribbean forearc is formed by a ~10 km-wide accretionary wedge. Here, drill Site U141 has revealed a record of frontal thrusts detached along biogenic ooze, which correlates lithologically with the "reference" Site U1381. This biogenic ooze contains >70% of organic components.There are up to 15% silica-rich elements in the upper part of the formation, while clay increases downsection. The biogenic ooze is overlain by silty clay, in which smectite is the dominant mineral. Low- to high-velocity friction experiments were performed on the biogenic ooze and the silty clay to investigate the velocity dependence of friction and the micromechanical foundation of strain localization within fontal thrusts. These experiments were performed at slip-rates of 3 µms-1 to 3.5 ms-1and σn up to 12 MPa, under both room-humidity and water saturated conditions. These experimental results indicate that, at low slip-rates, the biogenic ooze is stronger than the silty clay. At increasing slip-rates silty clays have a positive dependence of friction, while biogenic oozes show a sharp decrease of their friction coefficient as slip-rate increases. This rate-weakening behavior of the biogenic oozes may enhance co-seismic slip along the megathrust. The implication of these mechanical measurements is that the geological structures found in the forearc toe offshore SE Costa Rica were formed by locally high slip-rates that have enhanced slip propagation to the trench. Under slow slip-rates, deformation can have localized easier by creeping within the clays than in the oozes as seen. As Tsunami earthquakes are known to form with pronounced slip-to-the trench, the presence of biogenic oozes could be an indicator for past and potential tsunamigenic events. If so, this would be the case for the MAT from Guatemala to Costa Rica where similar biogenic ooze is found at all drill sites. Specifically, biogenic ooze may have formed the slip surface of the 1992 Nicaragua tsunami EQ. This needs to be tested.

The Hills are Alive: Dynamic Ridges and Valleys in a Strike-Slip Environment

NASA Astrophysics Data System (ADS)

Duvall, A. R.; Tucker, G. E.

2014-12-01

Strike-slip fault zones have long been known for characteristic landforms such as offset and deflected rivers, linear strike-parallel valleys, and shutter ridges. Despite their common presence, questions remain about the mechanics of how these landforms arise or how their form varies as a function of slip rate, geomorphic process, or material properties. We know even less about what happens far from the fault, in drainage basin headwaters, as a result of strike-slip motion. Here we explore the effects of horizontal fault slip rate, bedrock erodibility, and hillslope diffusivity on river catchments that drain across an active strike-slip fault using the CHILD landscape evolution model. Model calculations demonstrate that lateral fault motion induces a permanent state of landscape disequilibrium brought about by fault offset-generated river lengthening alternating with abrupt shortening due to stream capture. This cycle of shifting drainage patterns and base level change continues until fault motion ceases thus creating a perpetual state of transience unique to strike-slip systems. Our models also make the surprising prediction that, in some cases, hillslope ridges oriented perpendicular to the fault migrate laterally in conjunction with fault motion. Ridge migration happens when slip rate is slow enough and/or diffusion and river incision are fast enough that the hillslopes can respond to the disequilibrium brought about by strike-slip motion. In models with faster slip rates, stronger rocks or less-diffusive hillslopes, ridge mobility is limited or arrested despite the fact that the process of river lengthening and capture continues. Fast-slip cases also develop prominent steep fault-facing hillslope facets proximal to the fault valley and along-strike topographic profiles with reduced local relief between ridges and valleys. Our results demonstrate the dynamic nature of strike-slip landscapes that vary systematically with a ratio of bedrock erodibility (K) and hillslope diffusivity (D) to the rate of horizontal advection of topography (v). These results also reveal a potential set of recognizable geomorphic signatures within strike-slip systems that should be looked to as indicators of fault activity and/or material properties.

The role of capital realignment versus in situ stabilization for the treatment of slipped capital femoral epiphysis.

PubMed

Souder, Christopher D; Bomar, James D; Wenger, Dennis R

2014-12-01

Slipped capital femoral epiphysis (SCFE) can be treated by a variety of methods with the traditional method of in situ pin fixation being most commonly used. More recently, the Modified Dunn (Mod. Dunn) procedure consisting of capital realignment has been popularized as a treatment method for SCFE, particularly for more severe cases. Over the last 5 years, our institution has selectively used this method for more complex cases. The purpose of this article is to evaluate the differences between these 2 treatment methods in terms of avascular necrosis (AVN) rate, reoperation rate, and complication rate. Eighty-eight hips that were surgically treated for SCFE between July 2004 and June 2012 met our inclusion criteria. The in situ fixation group included 71 hips, whereas 17 hips were anatomically reduced with the Mod. Dunn procedure. Loder classification, severity, acuity, complication rate, and reoperation rate were determined for the 2 cohorts. The χ analysis was performed to evaluate the relationship between the treatment method and outcome. As expected, stable slips did well with in situ pinning with no cases of AVN, even in more severe slips. Ten stable slips were treated with the Mod. Dunn approach and 2 (20%) developed AVN. Unstable slips were more difficult to treat with 3 of the 7 hips stabilized in situ developing AVN (43%). Two of the 7 unstable slips treated by the Mod. Dunn procedure developed AVN (29%). The other outcomes studied (reoperation rate and complication rate) were not significantly related to the surgical treatment method (P = 0.732 and 0.261, respectively). In situ pinning remains a safe and predictable method for treatment of stable SCFE with no AVN noted, even in severe slips. Attempts to anatomically reduce stable slips led to severe AVN in 20% of cases, thus this treatment approach should be considered with caution. Treatment of unstable slips remains problematic with high AVN rates noted whether treated by in situ fixation or capital realignment (Mod. Dunn). Level III retrospective comparative study.

Kinematic Modeling of the 2011, Mw7.1 Van, Eastern Turkey Earthquake Using Teleseismic, Regional and GPS Data

NASA Astrophysics Data System (ADS)

Konca, A.

2013-12-01

A kinematic model for the Mw7.1 2011 Van Earthquake was obtained using regional, teleseismic and GPS data. One issue regarding regional data is that 1D Green's functions may not be appropriate due to complications in the upper mantle and crust that affects the Pnl waveforms. In order to resolve whether the 1D Green's function is appropriate, an aftershock of the main event was also modeled, which is then used as a criterion in the selection of the regional stations. The GPS data itself is not sufficient to obtain a slip model, but helps constrain the slip distribution. The slip distribution is up-dip and bilateral with more slip toward west, where the maximum slip reaches 4 meters. The rupture velocity is about 1.5 km/s.

Stick-slip instabilities in sheared granular flow: The role of friction and acoustic vibrations.

PubMed

Lieou, Charles K C; Elbanna, Ahmed E; Langer, J S; Carlson, J M

2015-08-01

We propose a theory of shear flow in dense granular materials. A key ingredient of the theory is an effective temperature that determines how the material responds to external driving forces such as shear stresses and vibrations. We show that, within our model, friction between grains produces stick-slip behavior at intermediate shear rates, even if the material is rate strengthening at larger rates. In addition, externally generated acoustic vibrations alter the stick-slip amplitude, or suppress stick-slip altogether, depending on the pressure and shear rate. We construct a phase diagram that indicates the parameter regimes for which stick-slip occurs in the presence and absence of acoustic vibrations of a fixed amplitude and frequency. These results connect the microscopic physics to macroscopic dynamics and thus produce useful information about a variety of granular phenomena, including rupture and slip along earthquake faults, the remote triggering of instabilities, and the control of friction in material processing.

A fault-based model for crustal deformation, fault slip-rates and off-fault strain rate in California

USGS Publications Warehouse

Zeng, Yuehua; Shen, Zheng-Kang

2016-01-01

We invert Global Positioning System (GPS) velocity data to estimate fault slip rates in California using a fault‐based crustal deformation model with geologic constraints. The model assumes buried elastic dislocations across the region using Uniform California Earthquake Rupture Forecast Version 3 (UCERF3) fault geometries. New GPS velocity and geologic slip‐rate data were compiled by the UCERF3 deformation working group. The result of least‐squares inversion shows that the San Andreas fault slips at 19–22  mm/yr along Santa Cruz to the North Coast, 25–28  mm/yr along the central California creeping segment to the Carrizo Plain, 20–22  mm/yr along the Mojave, and 20–24  mm/yr along the Coachella to the Imperial Valley. Modeled slip rates are 7–16  mm/yr lower than the preferred geologic rates from the central California creeping section to the San Bernardino North section. For the Bartlett Springs section, fault slip rates of 7–9  mm/yr fall within the geologic bounds but are twice the preferred geologic rates. For the central and eastern Garlock, inverted slip rates of 7.5 and 4.9  mm/yr, respectively, match closely with the geologic rates. For the western Garlock, however, our result suggests a low slip rate of 1.7  mm/yr. Along the eastern California shear zone and southern Walker Lane, our model shows a cumulative slip rate of 6.2–6.9  mm/yr across its east–west transects, which is ∼1  mm/yr increase of the geologic estimates. For the off‐coast faults of central California, from Hosgri to San Gregorio, fault slips are modeled at 1–5  mm/yr, similar to the lower geologic bounds. For the off‐fault deformation, the total moment rate amounts to 0.88×1019  N·m/yr, with fast straining regions found around the Mendocino triple junction, Transverse Ranges and Garlock fault zones, Landers and Brawley seismic zones, and farther south. The overall California moment rate is 2.76×1019  N·m/yr, which is a 16% increase compared with the UCERF2 model.

Co-seismic and cumulative slip along the Kokoxili Mw 7.9 earthquake rupture (Kunlun Fault, northeastern Tibet)

NASA Astrophysics Data System (ADS)

van der Woerd, J.; Klinger, Y.; Xu, X.; Ledortz, K.; Tapponnier, P.; Li, H.; King, G.; Ma, W.; Chen, W.

2009-04-01

Co-seismic slip values along a strike-slip rupture are found to be very irregular with variations up to one order of magnitude. Data usually scattered and sparse, are more dense and continuous with slip functions derived from InSAR or image correlations. Whether the fast variations in slip along strike reveals long-lived structures of the fault plane at depth, only incomplete slip at the surface or inelastic accommodation of slip remains debated. In addition, how these slip disparities are accommodated with time is unclear. The surface breaks of the Kokoxili Mw 7.9 event sytematically follow the geomorphic trace of the fault, which bears evidence for cumulative displacements. In the epicentral area, the rupture steps along the highest ice-capped summit of the region, the Buka Daban Feng. Evidence for normal fault breaks, left-lateral ruptures and steep triangular facets indicate that the Buka Daban Feng, a 40 km-long range reaching about 6800 m a.s.l. formed as a result of continuous oblique left-normal faulting. Normal faulting is attested by hanging glaciers, a steep southeastern flank and hot springs along coseismic and cumulative surface ruptures. Left-lateral movement along the main oblique normal fault has displaced the distal frontal moraines of almost all glacial valleys. West of the Buka Daban Feng, the western most ruptured strand is continuous between Kushiwan and Tayang lakes (about 60 km long) with coseismic left-lateral offsets reaching 4-5 m. To the east, at one site, the rupture splays into 4 main, N90°E-striking strands across a 1200x300m pull-apart. Three strands show right-stepping scarps with maximum throws of 1 m. The northern strand shows 3 m of purely normal throw. On NS profiles, the coseismic subsidence of the pull-apart floor was about 2 m, 1/10th of its 20 m depth, consistent with the repetition of 10 comparable earthquakes. East of the pull-apart 5 +/- 0.2 m sinistral slip are measured on the single stranded rupture. A similar coseismic sinistral slip value (4.8 +/- 0.4 m), with a thrust throw of 0.75 m, is found across two lake shorelines (1 and 2.3 meters above lake level), about 1.5 km farther east. At one river channel site, 15 km farther east, we measured a larger coseismic sinistral offset. The lowest terrace riser, between the active river bed and the lowest terrace is offset by about 10 m. Two older terrace risers show cumulative offsets twice as large (about 20 m). The largest cumulative offset measured reaches 50 m. Thirty kilometers yet farther east, near a glacial outlet at the foot of the Yuxi Shan, 4 distinct rills are offset by 3.5 m along the main surface break while smaller offsets (1-1.5 m) characterize a secondary break 250 m southwards. We have investigated in more detail the co-seismic and paleo-seismic slip near the central part of the rupture, where a set of about 10 inset terraces is used to infer the slip history of the fault. The particularly low co-seismic slip value at the site, about 2.4 +/- 0.6 m, lower than the value derived from Spot image correlation or from Insar, follows a maximum slip value of about 8 m only a few kilometres to the west. Site interpretation from field data, total station measurements and high resolution Ikonos images allow to reconstruct the different riser offsets across the damaged rupture zone. 10Be cosmogenic nuclide exposure ages of cobbles from the surface of the terraces allow to constrain the age the terraces and to infer an average slip-rate of 10-15 mm/yr in good agreement with previous results along the fault. When a characteristic slip model is considered, and depending of the measurement method or location of coseismic slip, the recurrence time for events comparable to the Mw 7.9 Kokoxili event may vary from 200 to 800 years.

Slowing extrusion tectonics: Lowered estimate of post-Early Miocene slip rate for the Altyn Tagh fault

USGS Publications Warehouse

Yue, Y.; Ritts, B.D.; Graham, S.A.; Wooden, J.L.; Gehrels, G.E.; Zhang, Z.

2004-01-01

Determination of long-term slip rate for the Altyn Tagh fault is essential for testing whether Asian tectonics is dominated by lateral extrusion or distributed crustal shortening. Previous slip-history studies focused on either Quaternary slip-rate measurements or pre-Early Miocene total-offset estimates and do not allow a clear distinction between rates based on the two. The magmatic and metamorphic history revealed by SHRIMP zircon dating of clasts from Miocene conglomerate in the Xorkol basin north of the Altyn Tagh fault strikingly matches that of basement in the southern Qilian Shan and northern Qaidam regions south of the fault. This match requires that the post-Early Miocene long-term slip rate along the Altyn Tagh fault cannot exceed 10 mm/year, supporting the hypothesis of distributed crustal thickening for post-Early Miocene times. This low long-term slip rate and recently documented large pre-Early Miocene cumulative offset across the fault support a two-stage evolution, wherein Asian tectonics was dominated by lateral extrusion before the end of Early Miocene, and since then has been dominated by distributed crustal thickening and rapid plateau uplift. ?? 2003 Elsevier B.V. All rights reserved.

GPS Imaging of Time-Variable Earthquake Hazard: The Hilton Creek Fault, Long Valley California

NASA Astrophysics Data System (ADS)

Hammond, W. C.; Blewitt, G.

2016-12-01

The Hilton Creek Fault, in Long Valley, California is a down-to-the-east normal fault that bounds the eastern edge of the Sierra Nevada/Great Valley microplate, and lies half inside and half outside the magmatically active caldera. Despite the dense coverage with GPS networks, the rapid and time-variable surface deformation attributable to sporadic magmatic inflation beneath the resurgent dome makes it difficult to use traditional geodetic methods to estimate the slip rate of the fault. While geologic studies identify cumulative offset, constrain timing of past earthquakes, and constrain a Quaternary slip rate to within 1-5 mm/yr, it is not currently possible to use geologic data to evaluate how the potential for slip correlates with transient caldera inflation. To estimate time-variable seismic hazard of the fault we estimate its instantaneous slip rate from GPS data using a new set of algorithms for robust estimation of velocity and strain rate fields and fault slip rates. From the GPS time series, we use the robust MIDAS algorithm to obtain time series of velocity that are highly insensitive to the effects of seasonality, outliers and steps in the data. We then use robust imaging of the velocity field to estimate a gridded time variable velocity field. Then we estimate fault slip rate at each time using a new technique that forms ad-hoc block representations that honor fault geometries, network complexity, connectivity, but does not require labor-intensive drawing of block boundaries. The results are compared to other slip rate estimates that have implications for hazard over different time scales. Time invariant long term seismic hazard is proportional to the long term slip rate accessible from geologic data. Contemporary time-invariant hazard, however, may differ from the long term rate, and is estimated from the geodetic velocity field that has been corrected for the effects of magmatic inflation in the caldera using a published model of a dipping ellipsoidal magma chamber. Contemporary time-variable hazard can be estimated from the time variable slip rate estimated from the evolving GPS velocity field.

Geodetic slip rate estimates for the Alhama de Murcia and Carboneras faults in the SE Betics, Spain

NASA Astrophysics Data System (ADS)

Khazaradze, Giorgi; Echeverria, Anna; Masana, Eulàlia

2016-04-01

The Alhama de Murcia and the Carboneras faults are the most prominent geologic structures within the Eastern Betic Shear Zone (EBSZ), located in SE Spain. Using continuous and campaign GPS observations conducted during the last decade, we were able to confirm the continuing tectonic activity of these faults by quantifying their geodetic slip-rates and comparing the estimated values with the geological (including paleoseismological) observations. We find that the bulk of the observed deformation is concentrated around the Alhama de Murcia (AMF) and the Palomares (PF) faults. The geodetic horizontal slip rate (reverse-sinistral) of 1.5±0.3 mm/yr calculated for the AMF and PF fault system is in good agreement with geological observations at the AMF, as well as, the focal mechanism of the 2011 Lorca earthquake, suggesting a main role of the AMF. We also find that the geodetic slip rate of the Carboneras fault zone (CFZ) is almost purely sinistral strike-slip with a rate of 1.3±0.2 mm/yr along N48° direction, very similar to 1.1 mm/yr geologic slip-rate, estimated from recent onshore and offshore paleoseismic and geomorphologic studies. The fact the geodetic and the geologic slip-rates are similar at the AMF and CF faults, suggests that both faults have been tectonically active since Quaternary, slipping at approximately at constant rate of 1.1 to 1.8 mm/yr. Since the existing GPS data cannot discern whether the CFZ is slipping seismically or aseismically, we have intended to relate the on-going seismic activity to the slip-rates estimated using GPS. For this reason we compared seismic and geodetic strain rates, where the latter are larger than seismic strain rates, suggesting the presence of aseismic processes in the area. Nevertheless, due to the large earthquake recurrence intervals, we may be underestimating the seismic strain rates. The direction of the P and T average stress axes are in good agreement with geodetic principal strain rate axes. To summarize, in eastern Betics, Alhama de Murcia and Carboneras left-lateral faults are the most active faults and they play an important role in the regional plate convergence kinematics. The work has been supported by the Spanish Ministry of Science and Innovation projects: SHAKE (CGL2011-30005-C02-01), CHARMA (CGL2013-40828-R) and EVENT (CGL2006-12861-C02-01).

Viscous slip coefficients for binary gas mixtures measured from mass flow rates through a single microtube

NASA Astrophysics Data System (ADS)

Yamaguchi, H.; Takamori, K.; Perrier, P.; Graur, I.; Matsuda, Y.; Niimi, T.

2016-09-01

The viscous slip coefficient for helium-argon binary gas mixture is extracted from the experimental values of the mass flow rate through a microtube. The mass flow rate is measured by the constant-volume method. The viscous slip coefficient was obtained by identifying the measured mass flow rate through a microtube with the corresponding analytical expression, which is a function of the Knudsen number. The measurements were carried out in the slip flow regime where the first-order slip boundary condition can be applied. The measured viscous slip coefficients of binary gas mixtures exhibit a concave function of the molar ratio of the mixture, showing a similar profile with numerical results. However, from the detailed comparison between the measured and numerical values with the complete and incomplete accommodation at a surface, it is inappropriate to estimate the viscous slip coefficient for the mixture numerically by employing separately measured tangential momentum accommodation coefficient for each component. The time variation of the molar ratio in the downstream chamber was measured by sampling the gas from the chamber using the quadrupole mass spectrometer. In our measurements, it is indicated that the volume flow rate of argon is larger than that of helium because of the difference in the tangential momentum accommodation coefficient.

Persistent rupture terminations at a restraining bend from slip rates on the eastern Altyn Tagh fault

NASA Astrophysics Data System (ADS)

Elliott, A. J.; Oskin, M. E.; Liu-zeng, J.; Shao, Y.-X.

2018-05-01

Restraining double-bends along strike-slip faults inhibit or permit throughgoing ruptures depending on bend angle, length, and prior rupture history. Modeling predicts that for mature strike-slip faults in a regional stress regime characterized by simple shear, a restraining bend of >18° and >4 km length impedes propagating rupture. Indeed, natural evidence shows that the most recent rupture(s) of the Xorkoli section (90°-93°E) of the eastern Altyn Tagh fault (ATF) ended at large restraining bends. However, when multiple seismic cycles are considered in numerical dynamic rupture modeling, heterogeneous residual stresses enable some ruptures to propagate further, modulating whether the bends persistently serve as barriers. These models remain to be tested using observations of the cumulative effects of multiple earthquake ruptures. Here we investigate whether a large restraining double-bend on the ATF serves consistently as a barrier to rupture by measuring long-term slip rates around the terminus of its most recent surface rupture at the Aksay bend. Our results show a W-E decline in slip as the SATF enters the bend, as would be predicted from repeated rupture terminations there. Prior work demonstrated no Holocene slip on the central, most misoriented portion of the bend, while 19-79 m offsets suggest that multiple ruptures have occurred on the west side of the bend during the Holocene. Thus we conclude the gradient in the SATF's slip rate results from the repeated termination of earthquake ruptures there. However, a finite slip rate east of the bend represents the transmission of some slip, suggesting that a small fraction of ruptures may fully traverse or jump the double-bend. This agreement between natural observations of slip accumulation and multi-cycle models of fault rupture enables us to translate observed slip rates into insight about the dynamic rupture process of individual earthquakes as they encounter geometric complexities along faults.

Exploratory results from a new rotary shear designed to reproduce the extreme deformation conditions of crustal earthquakes

NASA Astrophysics Data System (ADS)

Di Toro, G.; Nielsen, S. B.; Spagnuolo, E.; Smith, S.; Violay, M. E.; Niemeijer, A. R.; Di Felice, F.; Di Stefano, G.; Romeo, G.; Scarlato, P.

2011-12-01

A challenging goal in experimental rock deformation is to reproduce the extreme deformation conditions typical of coseismic slip in crustal earthquakes: large slip (up to 50 m), slip rates (0.1-10 m/s), accelerations (> 10 m/s2) and normal stress (> 50 MPa). Moreover, fault zones usually contain non-cohesive rocks (gouges) and fluids. The integration of all these deformation conditions is such a technical challenge that there is currently no apparatus in the world that can reproduce seismic slip. Yet, the determination of rock friction at seismic slip rates remains one of the main unknowns in earthquake physics, as it cannot be determined (or very approximately) by seismic wave inversion analysis. In the last thirty years, rotary shear apparatus were designed that combine large normal stresses and slip but low slip rates (high-pressure rotary shears first designed by Tullis) or low normal stresses but large slip rates and slip (rotary shears first designed by Shimamoto). Here we present the results of experiments using a newly-constructed Slow to HIgh Velocity Apparatus (SHIVA), installed at INGV in Rome, which extends the combination of normal stress, slip and slip rate achieved by previous apparatus and reproduces the conditions likely to occur during an earthquake in the shallow crust. SHIVA uses two brushless engines (max power 300 kW, max torque 930 Nm) and an air actuator (thrust 5 tons) in a rotary shear configuration (nominally infinite displacement) to slide hollow rock cylinders (30/50 mm int./ext. diameter) at slip rates ranging from 10 micron/s up to 6.5 m/s, accelerations up to 80 m/s2 and normal stresses up to 50 MPa. SHIVA can also perform experiments in which the torque on the sample (rather than the slip rate) is progressively increased until spontaneous failure occurs: this experimental capability should better reproduce natural conditions. The apparatus is equipped with a sample chamber to carry out experiments in the presence of fluids (up to 15 MPa fluid pressure), devices to determine the fluid composition during sliding, a gouge sample holder (tested up to 34 MPa in normal stress), and an environmental/vacuum chamber connected to a mass spectrometer to measure gas release during frictional sliding. In particular, we will show: 1) the extremely low friction coefficients (often approaching zero) and short (few cm is some cases) slip weakening distances measured in experiments performed at large normal stress (<40MPa) and accelerations on cohesive rocks (carbonatic marbles and gabbros); 2) the spontaneous creep episodes, lasting a few mm to a few cm in slip, that precede the large stress drops typical of earthquake instabilities, observed in torque-controlled experiments on gabbro and marbles; 3) how the presence of free fluids (H2O) delays the onset of dynamic weakening in carbonatic rocks; 4) the experimental microstructures, produced at normal stresses up to 34 MPa and slip rates of 1-3 m/s, in calcite gouges that closely resemble those found in exhumed seismic fault zones.

Applications of Morphochronology to the Active Tectonics of Tibet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ryerson, F J; Tapponnier, P; Finkel, R C

2005-01-28

The Himalayas and the Tibetan Plateau were formed as a result of the collision of India and Asia, and provide an excellent opportunity to study the mechanical response of the continental lithosphere to tectonic stress. Geophysicists are divided in their views on the nature of this response advocating either (1) homogeneously distributed deformation with the lithosphere deforming as a fluid continuum or (2) deformation is highly localized with the lithosphere that deforms as a system of blocks. The resolution of this issue has broad implications for understanding the tectonic response of continental lithosphere in general. Homogeneous deformation is supported bymore » relatively low decadal, geodetic slip-rate estimates for the Altyn Tagh and Karakorum Faults. Localized deformation is supported by high millennial, geomorphic slip-rates constrained by both cosmogenic and radiocarbon dating on these faults. Based upon the agreement of rates determined by radiocarbon and cosmogenic dating, the overall linearity of offset versus age correlations, and on the plateau-wide correlation of landscape evolution and climate history, the disparity between geomorphic and geodetic slip-rate determinations is unlikely to be due to the effects of surface erosion on the cosmogenic age determinations. Similarly, based upon the consistency of slip-rates over various observation intervals, secular variations in slip-rate appear to persist no longer than 2000 years and are unlikely to provide reconciliation. Conversely, geodetic and geomorphic slip-rate estimates on the Kunlun fault, which does not have significant splays or associated thrust faults, are in good agreement, indicating that there is no fundamental reason why these complementary geodetic and geomorphic methods should disagree. Similarly, the geodetic and geomorphic estimates of shortening rates across the northeastern edge of the plateau are in reasonable agreement, and the geomorphic rates on individual thrust faults demonstrate a significant eastward decrease in the shortening rate. This rate decrease is consistent with the transfer of slip from the Altyn Tagh Fault (ATF) to genetically-related thrust mountain building at its terminus. Rates on the ATF suggest a similar decrease in rate, but the current data set is too small to be definitive. Overall, the high, late Pleistocene-Holocene, geomorphic slip velocities on the major strike-slip faults of Tibet, suggests that they absorb as much of India's convergence relative to Siberia as the Himalayan Main Frontal Thrust on the southern edge of the plateau.« less

A New Perspective on Fault Geometry and Slip Distribution of the 2009 Dachaidan Mw 6.3 Earthquake from InSAR Observations

PubMed Central

Liu, Yang; Xu, Caijun; Wen, Yangmao; Fok, Hok Sum

2015-01-01

On 28 August 2009, the northern margin of the Qaidam basin in the Tibet Plateau was ruptured by an Mw 6.3 earthquake. This study utilizes the Envisat ASAR images from descending Track 319 and ascending Track 455 for capturing the coseismic deformation resulting from this event, indicating that the earthquake fault rupture does not reach to the earth’s surface. We then propose a four-segmented fault model to investigate the coseismic deformation by determining the fault parameters, followed by inverting slip distribution. The preferred fault model shows that the rupture depths for all four fault planes mainly range from 2.0 km to 7.5 km, comparatively shallower than previous results up to ~13 km, and that the slip distribution on the fault plane is complex, exhibiting three slip peaks with a maximum of 2.44 m at a depth between 4.1 km and 4.9 km. The inverted geodetic moment is 3.85 × 1018 Nm (Mw 6.36). The 2009 event may rupture from the northwest to the southeast unilaterally, reaching the maximum at the central segment. PMID:26184210

A New Perspective on Fault Geometry and Slip Distribution of the 2009 Dachaidan Mw 6.3 Earthquake from InSAR Observations.

PubMed

Liu, Yang; Xu, Caijun; Wen, Yangmao; Fok, Hok Sum

2015-07-10

On 28 August 2009, the northern margin of the Qaidam basin in the Tibet Plateau was ruptured by an Mw 6.3 earthquake. This study utilizes the Envisat ASAR images from descending Track 319 and ascending Track 455 for capturing the coseismic deformation resulting from this event, indicating that the earthquake fault rupture does not reach to the earth's surface. We then propose a four-segmented fault model to investigate the coseismic deformation by determining the fault parameters, followed by inverting slip distribution. The preferred fault model shows that the rupture depths for all four fault planes mainly range from 2.0 km to 7.5 km, comparatively shallower than previous results up to ~13 km, and that the slip distribution on the fault plane is complex, exhibiting three slip peaks with a maximum of 2.44 m at a depth between 4.1 km and 4.9 km. The inverted geodetic moment is 3.85 × 10(18) Nm (Mw 6.36). The 2009 event may rupture from the northwest to the southeast unilaterally, reaching the maximum at the central segment.

Laboratory constraints on models of earthquake recurrence

USGS Publications Warehouse

Beeler, Nicholas M.; Tullis, Terry; Junger, Jenni; Kilgore, Brian D.; Goldsby, David L.

2014-01-01

In this study, rock friction ‘stick-slip’ experiments are used to develop constraints on models of earthquake recurrence. Constant-rate loading of bare rock surfaces in high quality experiments produces stick-slip recurrence that is periodic at least to second order. When the loading rate is varied, recurrence is approximately inversely proportional to loading rate. These laboratory events initiate due to a slip rate-dependent process that also determines the size of the stress drop [Dieterich, 1979; Ruina, 1983] and as a consequence, stress drop varies weakly but systematically with loading rate [e.g., Gu and Wong, 1991; Karner and Marone, 2000; McLaskey et al., 2012]. This is especially evident in experiments where the loading rate is changed by orders of magnitude, as is thought to be the loading condition of naturally occurring, small repeating earthquakes driven by afterslip, or low-frequency earthquakes loaded by episodic slip. As follows from the previous studies referred to above, experimentally observed stress drops are well described by a logarithmic dependence on recurrence interval that can be cast as a non-linear slip-predictable model. The fault’s rate dependence of strength is the key physical parameter. Additionally, even at constant loading rate the most reproducible laboratory recurrence is not exactly periodic, unlike existing friction recurrence models. We present example laboratory catalogs that document the variance and show that in large catalogs, even at constant loading rate, stress drop and recurrence co-vary systematically. The origin of this covariance is largely consistent with variability of the dependence of fault strength on slip rate. Laboratory catalogs show aspects of both slip and time predictability and successive stress drops are strongly correlated indicating a ‘memory’ of prior slip history that extends over at least one recurrence cycle.

Coseismic slip of two large Mexican earthquakes from teleseismic body waveforms - Implications for asperity interaction in the Michoacan plate boundary segment

NASA Astrophysics Data System (ADS)

Mendoza, Carlos

1993-05-01

The distributions and depths of coseismic slip are derived for the October 25, 1981 Playa Azul and September 21, 1985 Zihuatanejo earthquakes in western Mexico by inverting the recorded teleseismic body waves. Rupture during the Playa Azul earthquake appears to have occurred in two separate zones both updip and downdip of the point of initial nucleation, with most of the slip concentrated in a circular region of 15-km radius downdip from the hypocenter. Coseismic slip occurred entirely within the area of reduced slip between the two primary shallow sources of the Michoacan earthquake that occurred on September 19, 1985, almost 4 years later. The slip of the Zihuatanejo earthquake was concentrated in an area adjacent to one of the main sources of the Michoacan earthquake and appears to be the southeastern continuation of rupture along the Cocos-North America plate boundary. The zones of maximum slip for the Playa Azul, Zihuatanejo, and Michoacan earthquakes may be considered asperity regions that control the occurrence of large earthquakes along the Michoacan segment of the plate boundary.

Thermally activated phase slips of one-dimensional Bose gases in shallow optical lattices

NASA Astrophysics Data System (ADS)

Kunimi, Masaya; Danshita, Ippei

2017-03-01

We study the decay of superflow via thermally activated phase slips in one-dimensional Bose gases in a shallow optical lattice. By using the Kramers formula, we numerically calculate the nucleation rate of a thermally activated phase slip for various values of the filling factor and flow velocity in the absence of a harmonic trapping potential. Within the local density approximation, we derive a formula connecting the phase-slip nucleation rate with the damping rate of a dipole oscillation of the Bose gas in the presence of a harmonic trap. We use the derived formula to directly compare our theory with the recent experiment done by the LENS group [L. Tanzi et al., Sci. Rep. 6, 25965 (2016), 10.1038/srep25965]. From the comparison, the observed damping of dipole oscillations in a weakly correlated and small velocity regime is attributed dominantly to thermally activated phase slips rather than quantum phase slips.

Aseismic and seismic slip induced by fluid injection from poroelastic and rate-state friction modeling

NASA Astrophysics Data System (ADS)

Liu, Y.; Deng, K.; Harrington, R. M.; Clerc, F.

2016-12-01

Solid matrix stress change and pore pressure diffusion caused by fluid injection has been postulated as key factors for inducing earthquakes and aseismic slip on pre-existing faults. In this study, we have developed a numerical model that simulates aseismic and seismic slip in a rate-and-state friction framework with poroelastic stress perturbations from multi-stage hydraulic fracturing scenarios. We apply the physics-based model to the 2013-2015 earthquake sequences near Fox Creek, Alberta, Canada, where three magnitude 4.5 earthquakes were potentially induced by nearby hydraulic fracturing activity. In particular, we use the relocated December 2013 seismicity sequence to approximate the fault orientation, and find the seismicity migration spatiotemporally correlate with the positive Coulomb stress changes calculated from the poroelastic model. When the poroelastic stress changes are introduced to the rate-state friction model, we find that slip on the fault evolves from aseismic to seismic in a manner similar to the onset of seismicity. For a 15-stage hydraulic fracturing that lasted for 10 days, modeled fault slip rate starts to accelerate after 3 days of fracking, and rapidly develops into a seismic event, which also temporally coincides with the onset of induced seismicity. The poroelastic stress perturbation and consequently fault slip rate continue to evolve and remain high for several weeks after hydraulic fracturing has stopped, which may explain the continued seismicity after shut-in. In a comparison numerical experiment, fault slip rate quickly decreases to the interseismic level when stress perturbations are instantaneously returned to zero at shut-in. Furthermore, when stress perturbations are removed just a few hours after the fault slip rate starts to accelerate (that is, hydraulic fracturing is shut down prematurely), only aseismic slip is observed in the model. Our preliminary results thus suggest the design of fracturing duration and flow-back strategy, either allowing stress perturbations to passively dissipate in the medium or actively dropping to the pre-perturbation level, is essential to inducing seismic versus aseismic slip on pre-existing faults.

Influence of strain rate on the structure/property behavior of the alpha-2 alloy Ti-24.5Al-10.5Nb-1.5Mo

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gray, G.T. III; Hong, Sun Ig; Marquardt, B.J.

Preliminary dislocation g{center_dot}b analysis revealed that following room temperature deformation at low strain rate the majority of the dislocations are a-dislocations lying on basal planes, 2nd order pyramidal (a/2 + c) slip on [1211], and 1st order pyramidal a-slip on [1011]. Increasing the rate of deformation at room temperature to 6000 s{sup {minus}1} is seen to result in increased a-slip on prism planes and a decreased amount of basal slip. At high-strain-rates and elevated temperatures the substructure was seen to be generally similar to that observed following high-rate deformation at room temperature except for an increased amount of basal slipmore » and a somewhat higher incidence of 2nd order pyramidal slip. The defect generation and the rate sensitivity of Ti-24.5Al-10.5Nb-1.5Mo are discussed as a function of strain rate and temperature and contrasted to that observed in conventional titanium alloys and TiAl.« less

Fault-based PSHA of an active tectonic region characterized by low deformation rates: the case of the Lower Rhine Graben

NASA Astrophysics Data System (ADS)

Vanneste, Kris; Vleminckx, Bart; Camelbeeck, Thierry

2016-04-01

The Lower Rhine Graben (LRG) is one of the few regions in intraplate NW Europe where seismic activity can be linked to active faults, yet probabilistic seismic hazard assessments of this region have hitherto been based on area-source models, in which the LRG is modeled as a single or a small number of seismotectonic zones with uniform seismicity. While fault-based PSHA has become common practice in more active regions of the world (e.g., California, Japan, New Zealand, Italy), knowledge of active faults has been lagging behind in other regions, due to incomplete tectonic inventory, low level of seismicity, lack of systematic fault parameterization, or a combination thereof. The past few years, efforts are increasingly being directed to the inclusion of fault sources in PSHA in these regions as well, in order to predict hazard on a more physically sound basis. In Europe, the EC project SHARE ("Seismic Hazard Harmonization in Europe", http://www.share-eu.org/) represented an important step forward in this regard. In the frame of this project, we previously compiled the first parameterized fault model for the LRG that can be applied in PSHA. We defined 15 fault sources based on major stepovers, bifurcations, gaps, and important changes in strike, dip direction or slip rate. Based on the available data, we were able to place reasonable bounds on the parameters required for time-independent PSHA: length, width, strike, dip, rake, slip rate, and maximum magnitude. With long-term slip rates remaining below 0.1 mm/yr, the LRG can be classified as a low-deformation-rate structure. Information on recurrence interval and elapsed time since the last major earthquake is lacking for most faults, impeding time-dependent PSHA. We consider different models to construct the magnitude-frequency distribution (MFD) of each fault: a slip-rate constrained form of the classical truncated Gutenberg-Richter MFD (Anderson & Luco, 1983) versus a characteristic MFD following Youngs & Coppersmith (1985). The summed Anderson & Luco fault MFDs show a remarkably good agreement with the MFD obtained from the historical and instrumental catalog for the entire LRG, whereas the summed Youngs & Coppersmith MFD clearly underpredicts low to moderate magnitudes, but yields higher occurrence rates for M > 6.3 than would be obtained by simple extrapolation of the catalog MFD. The moment rate implied by the Youngs & Coppersmith MFDs is about three times higher, but is still within the range allowed by current GPS uncertainties. Using the open-source hazard engine OpenQuake (http://openquake.org/), we compute hazard maps for return periods of 475, 2475, and 10,000 yr, and for spectral periods of 0 s (PGA) and 1 s. We explore the impact of various parameter choices, such as MFD model, GMPE distance metric, and inclusion of a background zone to account for lower magnitudes, and we also compare the results with hazard maps based on area-source models. References: Anderson, J. G., and J. E. Luco (1983), Consequences of slip rate constraints on earthquake occurrence relations, Bull. Seismol. Soc. Am., 73(2), 471-496. Youngs, R. R., and K. J. Coppersmith (1985), Implications of fault slip rates and earthquake recurrence models to probabilistic seismic hazard estimates, Bull. Seismol. Soc. Am., 75(4), 939-964.

Shallow slip amplification and enhanced tsunami hazard unravelled by dynamic simulations of mega-thrust earthquakes

PubMed Central

Murphy, S.; Scala, A.; Herrero, A.; Lorito, S.; Festa, G.; Trasatti, E.; Tonini, R.; Romano, F.; Molinari, I.; Nielsen, S.

2016-01-01

The 2011 Tohoku earthquake produced an unexpected large amount of shallow slip greatly contributing to the ensuing tsunami. How frequent are such events? How can they be efficiently modelled for tsunami hazard? Stochastic slip models, which can be computed rapidly, are used to explore the natural slip variability; however, they generally do not deal specifically with shallow slip features. We study the systematic depth-dependence of slip along a thrust fault with a number of 2D dynamic simulations using stochastic shear stress distributions and a geometry based on the cross section of the Tohoku fault. We obtain a probability density for the slip distribution, which varies both with depth, earthquake size and whether the rupture breaks the surface. We propose a method to modify stochastic slip distributions according to this dynamically-derived probability distribution. This method may be efficiently applied to produce large numbers of heterogeneous slip distributions for probabilistic tsunami hazard analysis. Using numerous M9 earthquake scenarios, we demonstrate that incorporating the dynamically-derived probability distribution does enhance the conditional probability of exceedance of maximum estimated tsunami wave heights along the Japanese coast. This technique for integrating dynamic features in stochastic models can be extended to any subduction zone and faulting style. PMID:27725733

Slip Distribution of the 2008 Iwate-Miyagi Nairiku, Japan, Earthquake Inverted from PALSAR Data

NASA Astrophysics Data System (ADS)

Fukahata, Y.; Fukushima, Y.; Arimoto, M.

2008-12-01

On 14 June 2008, the Iwate-Miyagi Nairiku earthquake struck northeast Japan, where active seismicity has been observed under east-west compressional stress fields. According to the Japan Meteorological Agency, the magnitude and the hypocenter depth of the earthquake are 7.2 and 8 km, respectively. The earthquake is considered to have occurred on a west dipping reverse fault with a roughly north-south strike. The earthquake caused significant surface displacements, which were detected by PALSAR, a Synthetic Aperture Radar (SAR) onboard the Advanced Land Observing Satellite (ALOS) employed by the Japan Aerospace Exploration Agency (JAXA). Several pairs of PALSAR images are available to measure the coseismic displacements. InSAR data show up to 1 m of line-of-sight displacements both for ascending and descending paths. The pixel matching method was also used to obtain range and azimuth offset data around the epicentral region, where displacements were too large for the interferometric technique (see Fukushima (this meeting) in detail). We inverted the obtained SAR interferometric and pixel matching data to estimate slip distribution on the fault. Since the geometry of the fault are not well known, the inverse problem is non-linear. If the fault surface is assumed to be a flat plane, however, the non-linearity is weak. Following the method of Fukahata & Wright (2008), we resolved the weak non-linearity based on ABIC (Akaike"fs Bayesian Information Criterion). That is to say, the fault parameters (e.g. strike, dip and location) as well as the weight of smoothing parameter were objectively determined by minimizing ABIC. We first estimated slip distribution by assuming a pure dip slip for simplicity, since it has been reported that the dip slip component is dominant. Then, the optimal fault geometry was dip 26 and strike 203 degrees with the location passing through (140.90E, 38.97N). The maximum slip was more than 8 m and most slips concentrated at shallow depths (< 4 km). Without fixing the rake, a large slip area with the maximum slip of about 8 m concentrated in the shallow region was obtained again.

Geodetic slip solutions for the Mw=7.4 Champerico (Guatemala) subduction earthquake of November 7 2012

NASA Astrophysics Data System (ADS)

Ellis, Andria; DeMets, Charles; Briole, Pierre; Molina, Enrique; Flores, Omar; Rivera, Jeffrey; Lasserre, Cécile; Lyon-Caen, Hélène; Lord, Neal

2014-05-01

As the first large subduction thrust earthquake off the coast of western Guatemala in the past 50 years, the 7 November 2012 Mw=7.4 earthquake offers the first opportunity for a geodetic study of coseismic and postseismic behavior for a segment of the Middle America trench where frictional coupling makes a transition from weak coupling off the coast of El Salvador to strong coupling in southern Mexico. Processing of continuous GPS measurements at 19 stations in Guatemala, El Salvador, and southern Mexico, and at 7 campaign points in Guatemala defines a highly consistent pattern of coseismic offsets during the earthquake, ranging from 47±5 mm of SW movement just inland from the earthquake epicenter to a few mm at sites located in northern Guatemala. Inversions of these offsets to find their best-fitting fault-slip solution in an elastic half space give a geodetic earthquake moment ranging between 0.75 and 1.1 x 1020 Nm, slightly smaller than the seismic estimates that range between 1.2 and 1.45 x 1020 Nm. Slip inversion using a constant slip model, assuming 293° and 29° for the fault azimuth and dip angle, indicates a nearly reverse slip of 2.8 m (rake 78°) on a fault plane 42 km-long and 20 km-wide, centered at 26 km depth. A variable slip inversion indicates that slip concentrated above depths of 40 km may have extended updip to the trench and reached a maximum of only 0.8 m, less than one-sixth the maximum slip indicated by a recent slip solution (5.3 m) obtained from waveform inversion of seismological data. Detailed model comparisons will be discussed. Transient postseismic displacements have been recorded at the nearby continuous GPS sites with amplitudes reaching 20-25 mm at some stations. The duration of the phenomenon is short: using an exponential-decay model, the estimated decay time is 90 ± 10 days. This postseismic signal is consistent with afterslip along a significantly broader area (+50%) of the subduction interface than ruptured coseismically. These results will be discussed in the tectonic framework of the area.

The Baja California Borderland and the Neogene Evolution of the Pacific-North American Plate Boundary

NASA Astrophysics Data System (ADS)

Fletcher, J. M.; Eakins, B. W.

2001-12-01

New observational data on Neogene faulting in the borderland of Baja California places important constraints on tectonic models for the evolution of the Pacific-North American (P-NA) plate boundary and rifting in the Gulf of California. Neogene faults in the borderland range from strike slip to normal slip and accommodate integrated transtension. Most have east-facing escarpments and likely reactivate the former east-dipping accretionary complex. Numerous lines of evidence indicate that Neogene faults are still active and accomplish a significant component ( ~1-5 mm/yr) of Pacific-North American shearing. Quaternary volcanoes are found offshore and along the Pacific coastal margin, Quaternary marine terraces are warped and uplifted as high as 200 masl. Many of the offshore faults have fresh escarpments and cut Holocene sediments. Extensive arrays of Quaternary fault scarps are found throughout the coastal region and in Bahia Magdalena they are clearly associated with major faults that bound recently uplifted islands. A prominent band of seismicity follows the coast and eight earthquakes (Ms>5.0) were teleseismically recorded between 1973 and 1998. This evidence for active shearing indicates that the Baja microplate has not yet been completely transferred to the Pacific plate. The best lithologic correlation that can be used to define the total Neogene slip across the borderland faults is the offset between the Magdalena submarine fan and its Baja source terrane. The distal facies of the fan drilled during DSDP leg 63 is dominated by mudstone and siltstone that contain reworked Paleogene cocoliths derived from strata correlative with the Tepetate formation found throughout the borderland and fine-grained sandstone derived from a source terrane of granitoid basement. The Middle Miocene La Calera formation of the Cabo trough is one of many granitoid-clast syn-rift alluvial deposits that could form the continental counterpart of the submarine fan near the mouth of the proto-gulf. However, regardless of the exact source, the Magdalena fan must have been transported beyond a major submarine canyon system south of Todos Santos by 13.5 Ma when sedimentation rates significantly diminished. This places a maximum of { ~}200 km total slip on the borderland faults since 13.5 Ma. Alternatively, all components of the Magdalena fan could have been derived from reworking Cenozoic strata within the borderland. The sandstone facies could be derived from the Oligocene El Cien Fm., which is a granitoid clast conglomerate that overlies the Tepetate Fm. and crops out ~100 km west of La Paz. If true, the total slip across borderland faults may be only a few tens of kilometers. Key structural relations along the submarine Tosco-Abreojos fault system support this lower slip estimate including: relatively short ({ ~}30 km width) pull-apart basins, correlative strata on either side of the fault, and a strong pattern of splaying, which indicates a lateral termination only { ~}50 km to the SE of the Magdalena fan. These new observations require significant modifications to existing tectonic models, which usually assign { ~}300 km of offset to the borderland. Lower finite slip estimates suggest that the borderland may not have formed the main P-NA plate boundary and long-term Neogene slip rates need not be significantly different from Quaternary slip rates. Lower finite slip estimates also allow stronger correlations between Farallon derived microplates and the patterns of Neogene faulting, volcanism, topographic variations, and surface heat flow in the overlying continental crust of Baja California.

What can friction tell us about shallow megathrust slip behavior?

NASA Astrophysics Data System (ADS)

Ikari, M.; Kopf, A.; Hirose, T.

2012-12-01

In subduction zones, the updip propagation of great earthquake ruptures on plate boundary megathrusts is currently one of the most important questions in earth science, primarily because rupture that approaches the surface causes seafloor displacement, resulting in enormous tsunamis. Moreover, the extent of updip rupture propagation is a key factor in defining the magnitude of the earthquake itself. Within the depth limits of the seismogenic zone, velocity-weakening frictional behavior is essential for the nucleation of large-magnitude earthquake rupture. Results of friction experiments at low slip velocities (~10-6-10-4 m/s) have suggested that velocity-weakening tends to occur in frictionally strong materials (typically non-clay), which may act as asperities on fault surfaces. However, the role of frictional strength and velocity dependence in controlling the extent of rupture propagation beyond the updip limit of the seismogenic zone is still unclear. Low to high-velocity friction experiments have provided insights into fault strength evolution over slip velocities spanning ~10 orders of magnitude, from plate convergence rates to coseismic slip rates. Results using primarily non-clay materials typically exhibit high friction at low velocities that progressively weakens at higher velocities (velocity-weakening), becoming nearly frictionless at coseismic slip rates [Di Toro et al., 2011]. However, the shallow near-trench regions of subduction zones are typically rich in clay minerals which are weak (friction coefficient ≤ ~0.4) and velocity-strengthening at slip rates < 10-3 m/s. A compilation of friction experiments using samples from the Nankai Trough region offshore Japan obtained by scientific ocean drilling shows that this material exhibits such behavior at low to intermediate slip velocities. However, after reaching peak values at ~10-2 m/s, these materials also exhibit a precipitous drop in friction toward near-zero values at coseismic slip rates. This suggests that all geologic materials, regardless of composition, are extremely weak when coseismic slip rates are enforced. Therefore, the likelihood of near-trench rupture propagation in subduction zones depends critically on whether slip can reach velocities ≥ ~10-2 m/s, where dynamic weakening becomes dominant. This depends on whether the propagating earthquake rupture can overcome the overall strength of the fault gouge and/or velocity-strengthening behavior at low to intermediate slip rates. We discuss here the possibility of near-trench earthquake rupture at Nankai and other subduction zones on the basis of laboratory friction measurements.

Spatiotemporal evolution of a transient slip event on the San Andreas fault near Parkfield, California

USGS Publications Warehouse

Murray, J.R.; Segall, P.

2005-01-01

In 1993 several baselines of the two-color electronic distance meter (EDM) network at Parkfield, California, deviated from their long-term rates, coincident with anomalous observations from nearby strain meters and a creep meter, as well as an increase in microseismicity. Between October 1992 and December 1994, three M ??? 4.5 earthquakes occurred beneath Middle Mountain, near the hypocenter of the 1934 and 1966 Parkfield M6 events. We analyzed the two-color EDM data using a Kalman-filtering based technique to image the spatiotemporal evolution of slip on the fault at Parkfield between the mid-1980s and 2003. This method accounts for localized random walk motion of the geodetic monuments and a prominent seasonal signal that affects many baselines. We find that a slip rate increase occurred between January 1993 and July 1996 on the upper 8 km of the fault near Middle Mountain. The peak estimated slip rate during this time was 49 mm/yr, which exceeds the long-term geologic rate of ???35 mm/yr. The slip rate evolution appears episodic, with an initial modest increase after the M4.3 earthquake and a much larger jump following the shallower M4.7 event in December 1994. This temporal correlation between inferred slip and seismicity suggests that the moderate earthquakes triggered the aseismic fault slip. The EDM data cannot resolve whether transient slip propagated across the nucleation zone of the 1934 and 1966 M6 Parkfield earthquakes. However, transient slip and its associated stress release in the hypocentral area of previous Parkfield events is consistent with the nucleation of the 2004 M6 Parkfield earthquake elsewhere on the fault. Copyright 2005 by the American Geophysical Union.

Ferrimagnetic resonance signal produced by frictional heating: A new indicator of paleoseismicity

NASA Astrophysics Data System (ADS)

Fukuchi, Tatsuro; Mizoguchi, Kazuo; Shimamoto, Toshihiko

2005-12-01

High-speed fault slips during earthquakes may generate sufficient frictional heat to produce fused fault rocks such as pseudotachylyte. We have carried out high-speed slip tests using natural fault gouge to judge whether or not frictional heating universally occurs during seismic fault slips. In our shearing tests, natural fault gouge is put between two cylindrical silica glasses and sheared under a fixed axial stress of 0.61 MPa. Despite such a low stress near the Earth's surface, a darkened cohesive material resembling pseudotachylyte is made from the fault gouge along the edge of a circular shear plane when shearing at a high speed of 1500 rpm (the maximum slip rate reaches ˜1.96 m/s at the edge). Electron spin resonance measurements reveal that the darkened cohesive material has a strong ferrimagnetic resonance (FMR) signal, which is derived from bulky trivalent iron ions in ferrimagnetic iron oxides (γ-Fe2O3). The FMR signal is produced by the thermal dehydration of antiferromagnetic iron oxides (γ-FeOOH) in the fault gouge. This may be applicable to the detection of past heating during seismic fault slip. We thus attempt to reconstruct the temperature of frictional heat generated on the Nojima fault plane in the 1995 Kobe earthquake (M = 7.3) by inversion using the FMR signal. The computer simulation indicates that the frictional heat generated on the Nojima fault plane at ˜390 m depth may have attained ˜390°C during the 1995 Kobe earthquake. The temperature in the fault plane may have returned to its initial state after ˜1 year. This result suggests that a heat flow anomaly generated by faulting may be difficult to detect.

Surface slip during large Owens Valley earthquakes

NASA Astrophysics Data System (ADS)

Haddon, E. K.; Amos, C. B.; Zielke, O.; Jayko, A. S.; Bürgmann, R.

2016-06-01

The 1872 Owens Valley earthquake is the third largest known historical earthquake in California. Relatively sparse field data and a complex rupture trace, however, inhibited attempts to fully resolve the slip distribution and reconcile the total moment release. We present a new, comprehensive record of surface slip based on lidar and field investigation, documenting 162 new measurements of laterally and vertically displaced landforms for 1872 and prehistoric Owens Valley earthquakes. Our lidar analysis uses a newly developed analytical tool to measure fault slip based on cross-correlation of sublinear topographic features and to produce a uniquely shaped probability density function (PDF) for each measurement. Stacking PDFs along strike to form cumulative offset probability distribution plots (COPDs) highlights common values corresponding to single and multiple-event displacements. Lateral offsets for 1872 vary systematically from ˜1.0 to 6.0 m and average 3.3 ± 1.1 m (2σ). Vertical offsets are predominantly east-down between ˜0.1 and 2.4 m, with a mean of 0.8 ± 0.5 m. The average lateral-to-vertical ratio compiled at specific sites is ˜6:1. Summing displacements across subparallel, overlapping rupture traces implies a maximum of 7-11 m and net average of 4.4 ± 1.5 m, corresponding to a geologic Mw ˜7.5 for the 1872 event. We attribute progressively higher-offset lateral COPD peaks at 7.1 ± 2.0 m, 12.8 ± 1.5 m, and 16.6 ± 1.4 m to three earlier large surface ruptures. Evaluating cumulative displacements in context with previously dated landforms in Owens Valley suggests relatively modest rates of fault slip, averaging between ˜0.6 and 1.6 mm/yr (1σ) over the late Quaternary.

Numerical Simulations of Mechanical Erosion from below by Creep on Rate-State Faults

NASA Astrophysics Data System (ADS)

Werner, M. J.; Rubin, A. M.

2012-04-01

The aim of this study is to increase our understanding of how earthquakes nucleate on frictionally-locked fault patches that are loaded by the growing stress concentrations at their boundaries due to aseismic creep. Such mechanical erosion from below of locked patches has previously been invoked by Gillard et al. (1996) to explain accelerating seismicity and increases in maximum earthquake magnitude on a strike-slip streak (a narrow ribbon of tightly clustered seismicity) in Kilauea's East rift, and it might also play a role in the loading of major locked strike-slip faults by creep from below the seismogenic zone. Gillard et al. (1996) provided simple analytical estimates of the size of and moment release within the eroding edge of the locked zone that matched the observed seismicity in Kilauea's East rift. However, an obvious, similar signal has not consistently been found before major strike-slip earthquakes. Here, we use simulations to determine to what extent the simple estimates by Gillard et al. survive a wider range of geometric configurations and slip histories. The boundary between the locked and creeping sections at the base of the seismogenic zone is modeled as a gradual, continuous transition between steady-state velocity-strengthening at greater depth to velocity-weakening surroundings at shallow depth, qualitatively consistent with laboratory estimates of the temperature dependence of (a-b). The goal is to expand the range of possible outcomes to broaden our range of expectations for the behavior of the eroding edge of the locked zones.

Evolution of the stress fields in the Zagros Foreland Folded Belt using focal mechanisms and kinematic analyses: the case of the Fars salient, Iran

NASA Astrophysics Data System (ADS)

Sarkarinejad, Khalil; Zafarmand, Bahareh; Oveisi, Behnam

2018-03-01

The NW-SE trending Zagros orogenic belt was initiated during the convergence of the Afro-Arabian continent and the Iranian microcontinent in the Late Cretaceous. Ongoing convergence is confirmed by intense seismicity related to compressional stresses collision-related in the Zagros orogenic belt by reactivation of an early extensional faulting to latter compressional segmented strike-slip and dip-slip faulting. These activities are strongly related either to the deep-seated basement fault activities (deep-seated earthquakes) underlies the sedimentary cover or gently dipping shallow-seated décollement horizon of the rheological weak rocks of the infra-Cambrian Hormuz salt. The compressional stress regimes in the different units play an important role in controlling the stress conditions between the different units within the sedimentary cover and basement. A significant set of nearly N-S trending right-lateral strike-slip faults exists throughout the study area in the Fars area in the Zagros Foreland Folded Belt. Fault-slip and focal mechanism data were analyzed using the stress inversion method to reconstruct the paleo and recent stress conditions. The results suggest that the current direction of maximum principal stress averages N19°E, with N38°E that for the past from Cretaceous to Tertiary (although a few sites on the Kar-e-Bass fault yield a different direction). The results are consistent with the collision of the Afro-Arabian continent and the Iranian microcontinent. The difference between the current and paleo-stress directions indicates an anticlockwise rotation in the maximum principle stress direction over time. This difference resulted from changes in the continental convergence path, but was also influenced by the local structural evolution, including the lateral propagation of folds and the presence of several local décollement horizons that facilitated decoupling of the deformation between the basement and the sedimentary cover. The obliquity of the maximum compressional stress into the fault trends reveals a typical stress partitioning of thrust and strike-slip motion in the Kazerun, Kar-e-Bass, Sabz-Pushan, and Sarvestan fault zones that caused these fault zones behave as segmented strike-slip and dip-slip faults.

Unified description of the slip phenomena in sheared polymer films: A molecular dynamics study

NASA Astrophysics Data System (ADS)

Priezjev, Nikolai

2010-03-01

The dynamic behavior of the slip length in shear flow of polymer melts past atomically smooth surfaces is investigated using MD simulations. The polymer melt was modeled as a collection of FENE-LJ bead-spring chains. We consider shear flow conditions at low pressures and weak wall-fluid interaction energy so that fluid velocity profiles are linear throughout the channel at all shear rates examined. In agreement with earlier studies we confirm that for shear- thinning fluids the slip length passes through a local minimum at low shear rates and then increases rapidly at higher shear rates. We found that the rate dependence of the slip length depends on the lattice orientation at high shear rates. The MD results show that the ratio of slip length to viscosity follows a master curve when plotted as a function of a single variable that depends on the structure factor, contact density and temperature of the first fluid layer near the solid wall. The universal dependence of the slip length holds for a number of parameters of the interface: fluid density and structure (chain length), wall-fluid interaction energy, wall density, lattice orientation, thermal or solid walls.

Monte Carlo simulation for slip rate sensitivity analysis in Cimandiri fault area

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pratama, Cecep, E-mail: great.pratama@gmail.com; Meilano, Irwan; Nugraha, Andri Dian

Slip rate is used to estimate earthquake recurrence relationship which is the most influence for hazard level. We examine slip rate contribution of Peak Ground Acceleration (PGA), in probabilistic seismic hazard maps (10% probability of exceedance in 50 years or 500 years return period). Hazard curve of PGA have been investigated for Sukabumi using a PSHA (Probabilistic Seismic Hazard Analysis). We observe that the most influence in the hazard estimate is crustal fault. Monte Carlo approach has been developed to assess the sensitivity. Then, Monte Carlo simulations properties have been assessed. Uncertainty and coefficient of variation from slip rate formore » Cimandiri Fault area has been calculated. We observe that seismic hazard estimates is sensitive to fault slip rate with seismic hazard uncertainty result about 0.25 g. For specific site, we found seismic hazard estimate for Sukabumi is between 0.4904 – 0.8465 g with uncertainty between 0.0847 – 0.2389 g and COV between 17.7% – 29.8%.« less

Fault Slip Partitioning in the Eastern California Shear Zone-Walker Lane Belt: Pliocene to Late Pleistocene Contraction Across the Mina Deflection

NASA Astrophysics Data System (ADS)

Lee, J.; Stockli, D.; Gosse, J.

2007-12-01

Two different mechanisms have been proposed for fault slip transfer between the subparallel NW-striking dextral- slip faults that dominant the Eastern California Shear Zone (ECSZ)-Walker Lane Belt (WLB). In the northern WLB, domains of sinistral-slip along NE-striking faults and clockwise block rotation within a zone of distributed deformation accommodated NW-dextral shear. A somewhat modified version of this mechanism was also proposed for the Mina deflection, southern WLB, whereby NE-striking sinistral faults formed as conjugate faults to the primary zone of NW-dextral shear; clockwise rotation of the blocks bounding the sinistral faults accommodated dextral slip. In contrast, in the northern ECSZ and Mina deflection, domains of NE-striking pure dip-slip normal faults, bounded by NW-striking dextral-slip faults, exhibited no rotation; the proposed mechanism of slip transfer was one of right-stepping, high angle normal faults in which the magnitude of extension was proportional to the amount of strike-slip motion transferred. New geologic mapping, tectonic geomorphologic, and geochronologic data from the Queen Valley area, southern Mina deflection constrain Pliocene to late Quaternary fault geometries, slip orientations, slip magnitudes, and slip rates that bear on the mechanism of fault slip transfer from the relatively narrow northern ECSZ to the broad deformation zone that defines the Mina deflection. Four different fault types and orientations cut across the Queen Valley area: (1) The NE-striking normal-slip Queen Valley fault; (2) NE-striking sinistral faults; (3) the NW-striking dextral Coyote Springs fault, which merges into (4) a set of EW-striking thrust faults. (U-Th)/He apatite and cosmogenic radionuclide data, combined with magnitude of fault offset measurements, indicate a Pliocene to late Pleistocene horizontal extension rate of 0.2-0.3 mm/yr across the Queen Valley fault. Our results, combined with published slip rates for the dextral White Mountain fault zone (0.3-0.8 mm/yr) and the eastern sinistral Coaldale fault (0.4 mm/yr) suggest that transfer of dextral slip from the narrow White Mountains fault zone is explained best by a simple shear couple whereby slip is partitioned into three different components: horizontal extension along the Queen Valley fault, dominantly dextral slip along the Coyote Springs fault, and dominantly sinistral slip along the Coaldale fault. A velocity vector diagram illustrating fault slip partitioning predicts contraction rates of <0.1 to 0.5 mm/yr across the Coyote Springs and western Coaldale faults. The predicted long-term contraction across the Mina deflection is consistent with present-day GPS data.

Temporal slip-rate stability and variations on the Hope Fault, New Zealand, during the late Quaternary

NASA Astrophysics Data System (ADS)

Khajavi, Narges; Nicol, Andrew; Quigley, Mark C.; Langridge, Robert M.

2018-07-01

The Hope Fault transfers slip from Hikurangi subduction to the Alpine Fault in the northern South Island of New Zealand. It accommodates mainly dextral strike slip and currently carries the highest slip rate in the Marlborough Fault System. Displacements, displacement rates and earthquake recurrence intervals have been determined using a combination of high resolution LiDAR for 59 dextral displacements ( 2.5-200 m) together with calibrated radiocarbon ages ( 130 yr to 13,000 yr) for abandoned stream channels, terrace risers and alluvial fans. Mean single-event displacement (SED) of 3 ± 0.6 m (2.2 to 4.6 m for 21 measurements) and mean recurrence interval of 266 ± 100 yr (range 128 to 560 yr) have been determined for the five most recent surface-rupturing earthquakes. On time scales ≥2300 yr the dextral slip rate is uniform at 12.2 ± 2.4 mm/yr, however, when averaged over time intervals of 230 to 1700 yr slip rates range from 4 to 46.4 mm/yr. This order-of-magnitude variability in slip rate over shorter timescales cannot be fully attributed to errors in displacement and age data, and is at least partly due to variations in earthquake recurrence interval and inferred SED. Short-term non-characteristic earthquake behaviour may be due to changes in fault loading arising from stress interactions between different segments of the Hope Fault and nearby faults.

Denali fault slip rates and Holocene-late Pleistocene kinematics of central Alaska

USGS Publications Warehouse

Matmon, A.; Schwartz, D.P.; Haeussler, Peter J.; Finkel, R.; Lienkaemper, J.J.; Stenner, Heidi D.; Dawson, T.E.

2006-01-01

The Denali fault is the principal intracontinental strike-slip fault accommodating deformation of interior Alaska associated with the Yakutat plate convergence. We obtained the first quantitative late Pleistocene-Holocene slip rates on the Denali fault system from dating offset geomorphic features. Analysis of cosmogenic 10Be concentrations in boulders (n = 27) and sediment (n = 13) collected at seven sites, offset 25-170 m by the Denali and Totschunda faults, gives average ages that range from 2.4 ± 0.3 ka to 17.0 ± 1.8 ka. These offsets and ages yield late Pleistocene-Holocene average slip rates of 9.4 ± 1.6, 12.1 ± 1.7, and 8.4 ± 2.2 mm/yr-1 along the western, central, and eastern Denali fault, respectively, and 6.0 ± 1.2 mm/yr-1 along the Totschunda fault. Our results suggest a westward decrease in the mean Pleistocene-Holocene slip rate. This westward decrease likely results from partitioning of slip from the Denali fault system to thrust faults to the north and west. 2006 Geological Society of America.

Extension of the Helmholtz-Smoluchowski velocity to the hydrophobic microchannels with velocity slip.

PubMed

Park, H M; Kim, T W

2009-01-21

Electrokinetic flows through hydrophobic microchannels experience velocity slip at the microchannel wall, which affects volumetric flow rate and solute retention time. The usual method of predicting the volumetric flow rate and velocity profile for hydrophobic microchannels is to solve the Navier-Stokes equation and the Poisson-Boltzmann equation for the electric potential with the boundary condition of velocity slip expressed by the Navier slip coefficient, which is computationally demanding and defies analytic solutions. In the present investigation, we have devised a simple method of predicting the velocity profiles and volumetric flow rates of electrokinetic flows by extending the concept of the Helmholtz-Smoluchowski velocity to microchannels with Navier slip. The extended Helmholtz-Smoluchowski velocity is simple to use and yields accurate results as compared to the exact solutions. Employing the extended Helmholtz-Smoluchowski velocity, the analytical expressions for volumetric flow rate and velocity profile for electrokinetic flows through rectangular microchannels with Navier slip have been obtained at high values of zeta potential. The range of validity of the extended Helmholtz-Smoluchowski velocity is also investigated.

Geodetic evidence for continuing tectonic activity of the Carboneras fault (SE Spain)

NASA Astrophysics Data System (ADS)

Echeverria, Anna; Khazaradze, Giorgi; Asensio, Eva; Masana, Eulalia

2015-11-01

The Carboneras fault zone (CFZ) is a prominent onshore-offshore strike-slip fault that forms part of the Eastern Betic Shear Zone (EBSZ), located in SE Spain. In this work, we show for the first time, the continuing tectonic activity of the CFZ and quantify its geodetic slip-rates using continuous and campaign GPS observations conducted during the last decade. We find that the left-lateral motion dominates the kinematics of the CFZ, with a strike-slip rate of 1.3 ± 0.2 mm/yr along the N48° direction. The shortening component is significantly lower and poorly constrained. Recent onshore and offshore paleoseismic and geomorphic results across the CFZ suggest a minimum Late Pleistocene to present-day strike-slip rate of 1.1 mm/yr. Considering the similarity of the geologic and geodetic slip rates measured at different points along the fault, the northern segment of the CFZ must have been slipping approximately at a constant rate during the Quaternary. Regarding the eastern Alpujarras fault zone corridor (AFZ), located to the north of the CFZ, our GPS measurements corroborate that this zone is active and exhibits a right-lateral motion. These opposite type strike-slip motion across the AFZ and CFZ is a result of a push-type force due to Nubia and Eurasia plate convergence, which, in turn, causes the westward escape of the block bounded by these two fault zones.

Stress shadow prohibits low interseismic coupling on shallow megathrusts, even where they are frictionally unlocked

NASA Astrophysics Data System (ADS)

Lindsey, E. O.; Almeida, R. V.; Bradley, K. E.; Hubbard, J.; Sathiakumar, S.; Mallick, R.; Barbot, S.; Hill, E.

2017-12-01

The possibility of large coseismic slip on the shallow part of megathrusts represents a significant hazard, due to both tsunami risk (for subduction zones) and strong seismic shaking hazard (for subaerial megathrusts). Laboratory experiments have long suggested that the shallow part of these faults may be frictionally unlocked. However, evidence for the predicted shallow creep remains scarce, and in the case of more accessible subaerial megathrusts such as the Himalaya, appears to be virtually absent. We propose that the lack of shallow creep can be due to the presence of a stress shadow from the down-dip locked portion of the fault and therefore that interseismic geodetic observations (even at the seafloor) are typically insufficient to constrain the frictional locking on the shallow portion of the fault. We use a boundary element model with rate-strengthening friction up-dip of a locked fault segment and find that a coupling value of zero at the trench is physically unrealistic even if only a small portion of the downdip fault zone is locked. For a typical subduction zone fault geometry which is frictionally unlocked from the surface to half the maximum seismogenic depth (considered an extreme case) we find that a coupling ratio of less than 0.7 at the trench is prohibited under most conditions. For a narrower zone of up-dip unlocking, the coupling ratio should be even higher. This result highlights the difference between frictional locking (a mechanical parameter) and geodetic coupling (a kinematic parameter), and indicates that published models of coupling that assume or predict low coupling at the trench need to be reevaluated. To assess how the up-dip slip deficit is ultimately released in the case of a frictionally unlocked (but geodetically coupled) zone, we conduct a series of earthquake cycle models based on rate- and state-dependent friction in two and three dimensions. The results show that strain in the shallow part of the fault is typically released as coseismic and postseismic slip, except under conditions favoring nucleation of shallow earthquakes or SSEs. During the interseismic period, our results suggest that seafloor geodetic instruments with an uncertainty of cm/yr may not have the resolution to distinguish shallow frictional locking (with zero slip) from unlocking (with slip <30% of plate rate).

Effects of Processing Parameters on the Forming Quality of C-Shaped Thermosetting Composite Laminates in Hot Diaphragm Forming Process

NASA Astrophysics Data System (ADS)

Bian, X. X.; Gu, Y. Z.; Sun, J.; Li, M.; Liu, W. P.; Zhang, Z. G.

2013-10-01

In this study, the effects of processing temperature and vacuum applying rate on the forming quality of C-shaped carbon fiber reinforced epoxy resin matrix composite laminates during hot diaphragm forming process were investigated. C-shaped prepreg preforms were produced using a home-made hot diaphragm forming equipment. The thickness variations of the preforms and the manufacturing defects after diaphragm forming process, including fiber wrinkling and voids, were evaluated to understand the forming mechanism. Furthermore, both interlaminar slipping friction and compaction behavior of the prepreg stacks were experimentally analyzed for showing the importance of the processing parameters. In addition, autoclave processing was used to cure the C-shaped preforms to investigate the changes of the defects before and after cure process. The results show that the C-shaped prepreg preforms with good forming quality can be achieved through increasing processing temperature and reducing vacuum applying rate, which obviously promote prepreg interlaminar slipping process. The process temperature and forming rate in hot diaphragm forming process strongly influence prepreg interply frictional force, and the maximum interlaminar frictional force can be taken as a key parameter for processing parameter optimization. Autoclave process is effective in eliminating voids in the preforms and can alleviate fiber wrinkles to a certain extent.

Grain size and shape evolution of experimentally deformed sediments: the role of slip rate

NASA Astrophysics Data System (ADS)

Balsamo, Fabrizio; Storti, Fabrizio; De Paola, Nicola

2016-04-01

Sediment deformation within fault zones occurs with a broad spectrum of mechanisms which, in turn, depend on intrinsic material properties (porosity, grain size and shape, etc.) and external factors (burial depth, fluid pressure, stress configuration, etc.). Fieldworks and laboratory measurements conducted in the last years in sediments faulted at shallow depth showed that cataclasis and grain size reduction can occur very close to the Earth surface (<1-2 km), and that fault displacement is one of the parameters controlling the amount of grain size, shape, and microtextural modifications in fault cores. In this contribution, we present a new set of microstructural observations combined with grain size and shape distribution data obtained from quart-feldspatic loose sediments (mean grain diameter 0.2 mm) experimentally deformed at different slip rates from subseismic (0.01 mm/s, 0.1 mm/s, 1 mm/s, 1 cm/s, and 10 cm/s) to coseismic slip rates (1 m/s). The experiments were originally performed at sigma n=14 MPa, with the same amount of slip (1.3 m), to constrain the frictional properties of such sediments at shallow confining pressures (<1 km). After the experiments, the granular materials deformed in the 0.1-1 mm-thick slip zones were prepared for both grain size distribution analyses and microstructural and textural analyses in thin sections. Grain size distribution analyses were obtained with a Malvern Mastersizer 3000 particle size laser-diffraction analyser, whereas grain shape data (angularity) were obtained by using image analysis technique on selected SEM-photomicrographs. Microstructural observations were performed at different scales with a standard optical microscope and with a SEM. Results indicate that mean grain diameter progressively decreases with increasing slip rates up to ~20-30 m, and that granulometric curves systematically modify as well, shifting toward finer grain sizes. Obtained fractal dimensions (D) indicate that D increases from ~2.3 up to >3 moving from subseismic to coseismic slip rates. Grain angularity also changes with increasing slip rates, being particles more smoothed and rounded in sediments deformed at coseismic slip rates. As a whole, our results indicate that both grain size and shape distributions of experimentally deformed sediments progressively changes from subseismic to coseismic slip rate, thus helping to understand the deformation mechanisms in natural fault zones and to predict frictional and permeability properties of faults affecting shallow sediments.

Coseismic slip distribution of the 1923 Kanto earthquake, Japan

USGS Publications Warehouse

Pollitz, F.F.; Nyst, M.; Nishimura, T.; Thatcher, W.

2005-01-01

The slip distribution associated with the 1923 M = 7.9 Kanto, Japan, earthquake is reexamined in light of new data and modeling. We utilize a combination of first-order triangulation, second-order triangulation, and leveling data in order to constrain the coseismic deformation. The second-order triangulation data, which have not been utilized in previous studies of 1923 coseismic deformation, are associated with only slightly smaller errors than the first-order triangulation data and expand the available triangulation data set by about a factor of 10. Interpretation of these data in terms of uniform-slip models in a companion study by Nyst et al. shows that a model involving uniform coseismic slip on two distinct rupture planes explains the data very well and matches or exceeds the fit obtained by previous studies, even one which involved distributed slip. Using the geometry of the Nyst et al. two-plane slip model, we perform inversions of the same geodetic data set for distributed slip. Our preferred model of distributed slip on the Philippine Sea plate interface has a moment magnitude of 7.86. We find slip maxima of ???8-9 m beneath Odawara and ???7-8 m beneath the Miura peninsula, with a roughly 2:1 ratio of strike-slip to dip-slip motion, in agreement with a previous study. However, the Miura slip maximum is imaged as a more broadly extended feature in our study, with the high-slip region continuing from the Miura peninsula to the southern Boso peninsula region. The second-order triangulation data provide good evidence for ???3 m right-lateral strike slip on a 35-km-long splay structure occupying the volume between the upper surface of the descending Philippine Sea plate and the southern Boso peninsula. Copyright 2005 by the American Geophysical Union.

On factors controlling precursor slip fronts in the laboratory and their relation to slow slip events in nature

NASA Astrophysics Data System (ADS)

Selvadurai, Paul A.; Glaser, Steven D.; Parker, Jessica M.

2017-03-01

Spatial variations in frictional properties on natural faults are believed to be a factor influencing the presence of slow slip events (SSEs). This effect was tested on a laboratory frictional interface between two polymethyl methacrylate (PMMA) bodies. We studied the evolution of slip and slip rates that varied systematically based on the application of both high and low normal stress (σ0=0.8 or 0.4 MPa) and the far-field loading rate (VLP). A spontaneous, frictional rupture expanded from the central, weaker, and more compliant section of the fault that had fewer asperities. Slow rupture propagated at speeds Vslow˜0.8 to 26 mm s-1 with slip rates from 0.01 to 0.2 μm s-1, resulting in stress drops around 100 kPa. During certain nucleation sequences, the fault experienced a partial stress drop, referred to as precursor detachment fronts in tribology. Only at the higher level of normal stress did these fronts exist, and the slip and slip rates mimicked the moment and moment release rates during the 2013-2014 Boso SSE in Japan. The laboratory detachment fronts showed rupture propagation speeds Vslow/VR∈ (5 to 172) × 10-7 and stress drops ˜ 100 kPa, which both scaled to the aforementioned SSE. Distributions of asperities, measured using a pressure sensitive film, increased in complexity with additional normal stress—an increase in normal stress caused added complexity by increasing both the mean size and standard deviation of asperity distributions, and this appeared to control the presence of the detachment front.

Post-seismic and interseismic fault creep I: model description

NASA Astrophysics Data System (ADS)

Hetland, E. A.; Simons, M.; Dunham, E. M.

2010-04-01

We present a model of localized, aseismic fault creep during the full interseismic period, including both transient and steady fault creep, in response to a sequence of imposed coseismic slip events and tectonic loading. We consider the behaviour of models with linear viscous, non-linear viscous, rate-dependent friction, and rate- and state-dependent friction fault rheologies. Both the transient post-seismic creep and the pattern of steady interseismic creep rates surrounding asperities depend on recent coseismic slip and fault rheologies. In these models, post-seismic fault creep is manifest as pulses of elevated creep rates that propagate from the coseismic slip, these pulses feature sharper fronts and are longer lived in models with rate-state friction compared to other models. With small characteristic slip distances in rate-state friction models, interseismic creep is similar to that in models with rate-dependent friction faults, except for the earliest periods of post-seismic creep. Our model can be used to constrain fault rheologies from geodetic observations in cases where the coseismic slip history is relatively well known. When only considering surface deformation over a short period of time, there are strong trade-offs between fault rheology and the details of the imposed coseismic slip. Geodetic observations over longer times following an earthquake will reduce these trade-offs, while simultaneous modelling of interseismic and post-seismic observations provide the strongest constraints on fault rheologies.

Assessing the performance of winter footwear using a new maximum achievable incline method.

PubMed

Hsu, Jennifer; Li, Yue; Dutta, Tilak; Fernie, Geoff

2015-09-01

More informative tests of winter footwear performance are required in order to identify footwear that will prevent injurious slips and falls on icy conditions. In this study, eight participants tested four styles of winter boots on smooth wet ice. The surface was progressively tilted to create increasing longitudinal and cross-slopes until participants could no longer continue standing or walking. Maximum achievable incline angles provided consistent measures of footwear slip resistance and demonstrated better resolution than mechanical tests. One footwear outsole material and tread combination outperformed the others on wet ice allowing participants to successfully walk on steep longitudinal slopes of 17.5° ± 1.9° (mean ± SD). By further exploiting the methodology to include additional surfaces and contaminants, such tests could be used to optimize tread designs and materials that are ideal for reducing the risk of slips and falls. Copyright © 2015 Elsevier Ltd and The Ergonomics Society. All rights reserved.

Optimum Sea Surface Displacement and Fault Slip Distribution of the 2017 Tehuantepec Earthquake (Mw 8.2) in Mexico Estimated From Tsunami Waveforms

NASA Astrophysics Data System (ADS)

Gusman, Aditya Riadi; Mulia, Iyan E.; Satake, Kenji

2018-01-01

The 2017 Tehuantepec earthquake (Mw 8.2) was the first great normal fault event ever instrumentally recorded to occur in the Middle America Trench. The earthquake generated a tsunami with an amplitude of 1.8 m (height = 3.5 m) in Puerto Chiapas, Mexico. Tsunami waveforms recorded at coastal tide gauges and offshore buoy stations were used to estimate the optimum sea surface displacement without assuming any fault. Our optimum sea surface displacement model indicated that the maximum uplift of 0.5 m is located near the trench and the maximum subsidence of 0.8 m on the coastal side near the epicenter. We then estimated the fault slip distribution that can best explain the optimum sea surface displacement assuming 10 different fault geometries. The best model suggests that a compact region of large slip (3-6 m) extends from a depth of 30 km to 90 km, centered at a depth of 60 km.

Holocene surface ruptures of the Rurrand Fault, Germany—insights from palaeoseismology, remote sensing and shallow geophysics

NASA Astrophysics Data System (ADS)

Grützner, Christoph; Fischer, Peter; Reicherter, Klaus

2016-03-01

The Lower Rhine Embayment in Central Europe hosts a rift system that has very low deformation rates. The faults in this area have slip rates of less than 0.1 mm yr-1, which does not allow to investigate ongoing tectonic deformation with geodetic techniques, unless they cover very long time spans. Instrumental seismicity does only cover a small fraction of the very long earthquake recurrence intervals of several thousands of years. Palaeoseismological studies are needed to constrain slip rates and the earthquake history of such faults. Destructive earthquakes are rare in the study area, but did occur in historic times. In 1755/1756, a series of strong earthquakes caused significant destruction in the city of Düren (Germany) and the surrounding areas. In this study we document palaeoseismological data from the nearby Rurrand Fault. In contrast to earlier studies on the same fault, we found evidence for a surface rupturing earthquake in the Holocene, and we identified at least one more surface rupturing event. Our study shows that the Rurrand Fault currently accommodates deformation in earthquakes rather than by creeping. The coseismic offsets were determined to be between less than 0.5 m per event. We assign maximum possible magnitudes of Mw 5.9-6.8 for the Rurrand Fault and a slip rate of at least 0.02-0.03 mm yr-1 for the last ˜130-50 kyr. The surface ruptures did not occur at the main fault trace that has a clear morphological expression due to older tectonic motions, but on a younger fault strand in the hanging wall of the main fault. Terrain analyses based on 1 m resolution airborne LiDAR data have been used to image the subtle morphological expression of this young fault zone. Georadar and electric resistivity tomography were applied to image the fault zone at depth and to test if these shallow geophysical methods can be used to identify and trace the fault zone. Georadar failed to produce reliable results, but geoelectrics were successfully applied and allowed us to retrieve slip rate estimates. Our results indicate that the Düren 1755/1756 earthquakes did not produce surface ruptures at the Rurrand Fault, either because they did not rupture the surface at all, or because they occurred at another, neighbouring fault.

Refining the shallow slip deficit

NASA Astrophysics Data System (ADS)

Xu, Xiaohua; Tong, Xiaopeng; Sandwell, David T.; Milliner, Christopher W. D.; Dolan, James F.; Hollingsworth, James; Leprince, Sebastien; Ayoub, Francois

2016-03-01

Geodetic slip inversions for three major (Mw > 7) strike-slip earthquakes (1992 Landers, 1999 Hector Mine and 2010 El Mayor-Cucapah) show a 15-60 per cent reduction in slip near the surface (depth < 2 km) relative to the slip at deeper depths (4-6 km). This significant difference between surface coseismic slip and slip at depth has been termed the shallow slip deficit (SSD). The large magnitude of this deficit has been an enigma since it cannot be explained by shallow creep during the interseismic period or by triggered slip from nearby earthquakes. One potential explanation for the SSD is that the previous geodetic inversions lack data coverage close to surface rupture such that the shallow portions of the slip models are poorly resolved and generally underestimated. In this study, we improve the static coseismic slip inversion for these three earthquakes, especially at shallow depths, by: (1) including data capturing the near-fault deformation from optical imagery and SAR azimuth offsets; (2) refining the interferometric synthetic aperture radar processing with non-boxcar phase filtering, model-dependent range corrections, more complete phase unwrapping by SNAPHU (Statistical Non-linear Approach for Phase Unwrapping) assuming a maximum discontinuity and an on-fault correlation mask; (3) using more detailed, geologically constrained fault geometries and (4) incorporating additional campaign global positioning system (GPS) data. The refined slip models result in much smaller SSDs of 3-19 per cent. We suspect that the remaining minor SSD for these earthquakes likely reflects a combination of our elastic model's inability to fully account for near-surface deformation, which will render our estimates of shallow slip minima, and potentially small amounts of interseismic fault creep or triggered slip, which could `make up' a small percentages of the coseismic SSD during the interseismic period. Our results indicate that it is imperative that slip inversions include accurate measurements of near-fault surface deformation to reliably constrain spatial patterns of slip during major strike-slip earthquakes.

Where did the time go? Friction evolves with slip following large velocity steps, normal stress steps, and (?) during long holds

NASA Astrophysics Data System (ADS)

Rubin, A. M.; Bhattacharya, P.; Tullis, T. E.; Okazaki, K.; Beeler, N. M.

2016-12-01

The popular constitutive formulations of rate-and-state friction offer two end-member views on whether friction evolves only with slip (Slip law state evolution) or with time even without slip (Aging law state evolution). While rate stepping experiments show support for the Slip law, laboratory observed frictional behavior of initially bare rock surfaces near zero slip rate has traditionally been interpreted to show support for time-dependent evolution of frictional strength. Such laboratory derived support for time-dependent evolution has been one of the motivations behind the Aging law being widely used to model earthquake cycles on natural faults.Through a combination of theoretical results and new experimental data on initially bare granite, we show stronger support for the other end member view, i.e. that friction under a wide range of sliding conditions evolves only with slip. Our dataset is unique in that it combines up to 3.5 orders of magnitude rate steps, sequences of holds up to 10000s, and 5% normal stress steps at order of magnitude different sliding rates during the same experimental run. The experiments were done on the Brown rotary shear apparatus using servo feedback, making the machine stiff enough to provide very large departures from steady-state while maintaining stable, quasi-static sliding. Across these diverse sliding conditions, and in particular for both large velocity step decreases and the longest holds, the data are much more consistent with the Slip law version of slip-dependence than the time-dependence formulated in the Aging law. The shear stress response to normal stress steps is also consistently better explained by the Slip law when paired with the Linker-Dieterich type response to normal stress perturbations. However, the remarkable symmetry and slip-dependence of the normal stress step increases and decreases suggest deficiencies in the Linker-Dieterich formulation that we will probe in future experiments.High quality measurements of interface compaction from the normal-stress steps suggest that the instantaneous changes in state and contact area are opposite in sign, indicating that state evolution might be fundamentally connected to contact quality, and not quantity alone.

Rock uplift above the subduction megathrust at Montague and Hinchinbrook Islands, Prince William Sound, Alaska

NASA Astrophysics Data System (ADS)

Ferguson, Kelly M.

Deformation related to the transition from strike-slip to convergent slip during flat-slab subduction of the Yakutat microplate has resulted in regions of focused rock uplift and exhumation. In the St. Elias and Chugach Mountains, faulting related to transpressional processes and bending of fault systems coupled with enhanced glacial erosion causes rapid exhumation. Underplating below the syntaxial bend farther west in the Chugach Mountains and central Prince William Sound causes focused, but less rapid, exhumation. Farther south in the Prince William Sound, plate boundary deformation transitions from strike-slip to nearly full convergence in the Montague Island and Hinchinbrook Island region, which is ˜20 km above the megathrust between the Yakutat microplate and overriding North American Plate. Montague and Hinchinbrook Islands are narrow, elongate, and steep, with a structural grain formed by several megathrust fault splays, some of which slipped during the 1964 M9.2 earthquake. Presented here are 32 new apatite (U-Th)/He (AHe) and 28 new apatite fission-track (AFT) ages from the Montague and Hinchinbrook Island regions. Most AHe ages are <5 Ma, with some as young as 1.1 Ma. AHe ages are youngest at the southwest end of Montague Island, where maximum fault displacement occurred on the Hanning Bay and Patton Bay faults during the 1964 earthquake. AFT ages range from ˜5 Ma to ˜20 Ma and are also younger at the SW end of Montague Island. These ages and corresponding exhumation rates indicate that the Montague and Hinchinbrook Island region is a narrow zone of intense deformation probably related to duplex thrusting along one or more megathrust fault splays. I interpret the rates of rock uplift and exhumation to have increased in the last ˜5 My, especially at the southwest end of the island system and farthest from the region dominated by strike-slip and transpressional deformation to the northeast. The narrow band of deformation along these islands likely represents the northwestern edge of a broader swath of plate boundary deformation between the Montague-Hinchinbrook Island region and the Kayak Island fault zone.

Implications of a 20-Hz Booster cycle-rate for Slip-stacking

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eldred, Jeffrey; Zwaska, Robert

2014-06-10

We examine the potential impacts to slip-stacking from a change of the Booster cycle-rate from 15- to 20-Hz. We find that changing the Booster cycle-rate to 20-Hz would greatly increase the slip-stacking bucket area, while potentially requiring greater usage of the Recycler momentum aperture and additional power dissipation in the RF cavities. In particular, the losses from RF interference can be reduced by a factor of 4-10 (depending on Booster beam longitudinal parameters). We discuss the aspect ratio and beam emittance requirements for efficient slip-stacking in both cycle-rate cases. Using a different injection scheme can eliminate the need for greatermore » momentum aperture in the Recycler.« less

A technique for measuring dynamic friction coefficient under impact loading

NASA Astrophysics Data System (ADS)

Lin, Y. L.; Qin, J. G.; Chen, R.; Zhao, P. D.; Lu, F. Y.

2014-09-01

We develop a novel setup based on the split Hopkinson pressure bar technique to test the dynamic friction coefficient under impact loading. In the setup, the major improvement is that the end of the incident bar near the specimen is wedge-shaped, which results in a combined compressive and shear loading applied to the specimen. In fact, the shear loading is caused by the interfacial friction between specimen and bars. Therefore, when the two loading force histories are measured, the friction coefficient histories can be calculated without any assumptions and theoretical derivations. The geometry of the friction pairs is simple, and can be either cuboid or cylindrical. Regarding the measurements, two quartz transducers are used to directly record the force histories, and an optical apparatus is designed to test the interfacial slip movement. By using the setup, the dynamic friction coefficient of PTFE/aluminum 7075 friction pairs was tested. The time resolved dynamic friction coefficient and slip movement histories were achieved. The results show that the friction coefficient changes during the loading process, the average data of the relatively stable flat plateau section of the friction coefficient curves is 0.137, the maximum normal pressure is 52 MPa, the maximum relative slip velocity is 1.5 m/s, and the acceleration is 8400 m2/s. Furthermore, the friction test was simulated using an explicit FEM code LS-DYNA. The simulation results showed that the constant pressure and slip velocity can both be obtained with a wide flat plateau incident pulse. For some special friction pairs, normal pressure up to a few hundred MPa, interfacial slip velocities up to 10 m/s, and slip movement up to centimeter-level can be expected.

A technique for measuring dynamic friction coefficient under impact loading.

PubMed

Lin, Y L; Qin, J G; Chen, R; Zhao, P D; Lu, F Y

2014-09-01

We develop a novel setup based on the split Hopkinson pressure bar technique to test the dynamic friction coefficient under impact loading. In the setup, the major improvement is that the end of the incident bar near the specimen is wedge-shaped, which results in a combined compressive and shear loading applied to the specimen. In fact, the shear loading is caused by the interfacial friction between specimen and bars. Therefore, when the two loading force histories are measured, the friction coefficient histories can be calculated without any assumptions and theoretical derivations. The geometry of the friction pairs is simple, and can be either cuboid or cylindrical. Regarding the measurements, two quartz transducers are used to directly record the force histories, and an optical apparatus is designed to test the interfacial slip movement. By using the setup, the dynamic friction coefficient of PTFE/aluminum 7075 friction pairs was tested. The time resolved dynamic friction coefficient and slip movement histories were achieved. The results show that the friction coefficient changes during the loading process, the average data of the relatively stable flat plateau section of the friction coefficient curves is 0.137, the maximum normal pressure is 52 MPa, the maximum relative slip velocity is 1.5 m/s, and the acceleration is 8400 m(2)/s. Furthermore, the friction test was simulated using an explicit FEM code LS-DYNA. The simulation results showed that the constant pressure and slip velocity can both be obtained with a wide flat plateau incident pulse. For some special friction pairs, normal pressure up to a few hundred MPa, interfacial slip velocities up to 10 m/s, and slip movement up to centimeter-level can be expected.

Earthquake slip weakening and asperities explained by thermal pressurization.

PubMed

Wibberley, Christopher A J; Shimamoto, Toshihiko

2005-08-04

An earthquake occurs when a fault weakens during the early portion of its slip at a faster rate than the release of tectonic stress driving the fault motion. This slip weakening occurs over a critical distance, D(c). Understanding the controls on D(c) in nature is severely limited, however, because the physical mechanism of weakening is unconstrained. Conventional friction experiments, typically conducted at slow slip rates and small displacements, have obtained D(c) values that are orders of magnitude lower than values estimated from modelling seismological data for natural earthquakes. Here we present data on fluid transport properties of slip zone rocks and on the slip zone width in the centre of the Median Tectonic Line fault zone, Japan. We show that the discrepancy between laboratory and seismological results can be resolved if thermal pressurization of the pore fluid is the slip-weakening mechanism. Our analysis indicates that a planar fault segment with an impermeable and narrow slip zone will become very unstable during slip and is likely to be the site of a seismic asperity.

Thermo-mechanical pressurization of experimental faults in cohesive rocks during seismic slip

NASA Astrophysics Data System (ADS)

Violay, M.; Di Toro, G.; Nielsen, S.; Spagnuolo, E.; Burg, J. P.

2015-11-01

Earthquakes occur because fault friction weakens with increasing slip and slip rates. Since the slipping zones of faults are often fluid-saturated, thermo-mechanical pressurization of pore fluids has been invoked as a mechanism responsible for frictional dynamic weakening, but experimental evidence is lacking. We performed friction experiments (normal stress 25 MPa, maximal slip-rate ∼3 ms-1) on cohesive basalt and marble under (1) room-humidity and (2) immersed in liquid water (drained and undrained) conditions. In both rock types and independently of the presence of fluids, up to 80% of frictional weakening was measured in the first 5 cm of slip. Modest pressurization-related weakening appears only at later stages of slip. Thermo-mechanical pressurization weakening of cohesive rocks can be negligible during earthquakes due to the triggering of more efficient fault lubrication mechanisms (flash heating, frictional melting, etc.).

Millennial slip-rates along the eastern Kunlun fault and rapid evolution of channel morphology in the yellow river headwaters, northeastern Tibet, China

NASA Astrophysics Data System (ADS)

Harkins, Nathan W.

A mechanical description of the interplay between ongoing crustal deformation and topographic evolution within the Tibetan Plateau remains outstanding, and thus our ability to describe the mechanisms responsible for the creation of this and other continental plateaus is limited. In this work, we employ a multidisciplinary approach to investigate the Quaternary record of active tectonism and coeval topographic evolution in the northeastern Tibetan Plateau. Fluvial channel topographic data paired with geochronologically calibrated measures of erosion rate reveal a headward migrating wave of dramatically accelerated incision rates in the headwaters of the Yellow River, which drains a large portion of northeastern Tibet. This transient increase in incision is likely driven by downstream base-level changes along the plateau margin and is superimposed onto a broad region of higher erosion rates confined to the plateau itself, within the Anyemaqen Shan (mountains). The Kunlun fault, one of the major active strike-slip faults of Tibet, trends through the Anyemaqen Shan. Using a careful approach towards quantifying millennial slip-rates along this fault zone based on the age of offset landforms, we constrain the Pleistocene kinematics of the eastern portion of the Kunlun fault and link this deformation to tectonically-driven erosion in the Anyemaqen Shan. Consideration of the age and morphology of fluvial terraces offset by the fault both highlights uncertainties associated with slip-rate determinations and allow more confident quantification of the allowable range of slip-rates at sites that take advantage of these features. Several new slip-rate determinations from this study at select locations corroborate a small number of previous determinations to identify an eastward decreasing slip-rate gradient and termination of the Kunlun fault within the Anyemaqen Shan. Existing geodetic data reveals a similar pattern of eastward-decreasing distributed shear across the fault zone. The spatial coincidence of tectonically driven erosion in the Anyemaqen Shan with the slip-rate gradient and termination the Kunlun fault implies that the crust of the northeastern plateau has the ability to accumulate regionally distributed permanent strain. Therefore, traditional 'rigid-body' rotation type descriptions of Tibetan Plateau kinematics fail to describe deformation on the northeastern plateau.

Seismic potential of weak, near-surface faults revealed at plate tectonic slip rates

PubMed Central

Ikari, Matt J.; Kopf, Achim J.

2017-01-01

The near-surface areas of major faults commonly contain weak, phyllosilicate minerals, which, based on laboratory friction measurements, are assumed to creep stably. However, it is now known that shallow faults can experience tens of meters of earthquake slip and also host slow and transient slip events. Laboratory experiments are generally performed at least two orders of magnitude faster than plate tectonic speeds, which are the natural driving conditions for major faults; the absence of experimental data for natural driving rates represents a critical knowledge gap. We use laboratory friction experiments on natural fault zone samples at driving rates of centimeters per year to demonstrate that there is abundant evidence of unstable slip behavior that was not previously predicted. Specifically, weak clay-rich fault samples generate slow slip events (SSEs) and have frictional properties favorable for earthquake rupture. Our work explains growing field observations of shallow SSE and surface-breaking earthquake slip, and predicts that such phenomena should be more widely expected. PMID:29202027

Length-Displacement Scaling of Lunar Thrust Faults and the Formation of Uphill-Facing Scarps

NASA Astrophysics Data System (ADS)

Hiesinger, Harald; Roggon, Lars; Hetzel, Ralf; Clark, Jaclyn D.; Hampel, Andrea; van der Bogert, Carolyn H.

2017-04-01

Lobate scarps are straight to curvilinear positive-relief landforms that occur on all terrestrial bodies [e.g., 1-3]. They are the surface manifestation of thrust faults that cut through and offset the upper part of the crust. Fault scarps on planetary surfaces provide the opportunity to study the growth of faults under a wide range of environmental conditions (e.g., gravity, temperature, pore pressure) [4]. We studied four lunar thrust-fault scarps (Simpelius-1, Morozov (S1), Fowler, Racah X-1) ranging in length from 1.3 km to 15.4 km [5] and found that their maximum total displacements are linearly correlated with length over one order of magnitude. We propose that during the progressive accumulation of slip, lunar faults propagate laterally and increase in length. On the basis of our measurements, the ratio of maximum displacement, D, to fault length, L, ranges from 0.017 to 0.028 with a mean value of 0.023 (or 2.3%). This is an order of magnitude higher than the value of 0.1% derived by theoretical considerations [4], and about twice as large as the value of 0.012-0.013 estimated by [6,7]. Our results, in addition to recently published findings for other lunar scarps [2,8], indicate that the D/L ratios of lunar thrust faults are similar to those of faults on Mercury and Mars (e.g., 1, 9-11], and almost as high as the average D/L ratio of 3% for faults on Earth [16,23]. Three of the investigated thrust fault scarps (Simpelius-1, Morozov (S1), Fowler) are uphill-facing scarps generated by slip on faults that dip in the same direction as the local topography. Thrust faults with such a geometry are common ( 60% of 97 studied scarps) on the Moon [e.g., 2,5,7]. To test our hypothesis that the surface topography plays an important role in the formation of uphill-facing fault scarps by controlling the vertical load on a fault plane, we simulated thrust faulting and its relation to topography with two-dimensional finite-element models using the commercial code ABAQUS (version 6.14). Our model results indicate that the onset of faulting in our 200-km-long model is a function of the surface topography [5]. Our numerical model indicates that uphill-facing scarps form earlier and grow faster than downhill-facing scarps under otherwise similar conditions. Thrust faults which dip in the same general direction as the topography (forming an uphill-facing scarp), start to slip earlier (4.2 Ma) after the onset of shortening and reach a total slip of 5.8 m after 70 Ma. In contrast, slip on faults that leads to the generation of a downhill-facing scarp initiates much later (i.e., after 20 Ma of elapsed model time) and attains a total slip of only 1.8 m in 70 Ma. If the surface of the model is horizontal, faulting on both fault structures starts after 4.4 Ma, but faulting proceeds at a lower rate than for fault, which generated the uphill-facing scarp. Although the absolute ages for fault initiation (as well as the total fault slip) depend on the arbitrarily chosen shortening rate (as well as on the size of the model and the elastic parameters), this relative timing of fault activation was consistently observed irrespective of the chosen shortening rate. Thus, the model results demonstrate that, for all other factors being equal, the differing weight of the hanging wall above the two modeled faults is responsible for the different timing of fault initiation and the difference in total slip. In conclusion, we present new quantitative estimates of the maximum total displacements of lunar lobate scarps and offer a new model to explain the origin of uphill-facing scarps that is also of importance for understanding the formation of the Lee-Lincoln scarp at the Apollo 17 landing site. [1] Watters et al., 2000, Geophys. Res. Lett. 27; [2] Williams et al., 2013, J. Geophys. Res. 118; [3] Massironi et al., 2015, Encycl. Planet. Landf., pp. 1255-1262; [4] Schultz et al., 2006, J. Struct. Geol. 28; [5] Roggon et al. (2017) Icarus, in press; [6] Watters and Johnson, 2010, Planetary Tectonics, pp. 121-182; [7] Banks et al., 2012, J. Geophys. Res. 117; [8] Banks et al., 2013, LPSC 44, 3042; [9] Hauber and Kronberg, 2005, J. Geophys. Res. 110; [10] Hauber et al., 2013, EPSC2013-987; [11] Byrne et al., 2014, Nature Geosci. 7

Slip accumulation and lateral propagation of active normal faults in Afar

NASA Astrophysics Data System (ADS)

Manighetti, I.; King, G. C. P.; Gaudemer, Y.; Scholz, C. H.; Doubre, C.

2001-01-01

We investigate fault growth in Afar, where normal fault systems are known to be currently growing fast and most are propagating to the northwest. Using digital elevation models, we have examined the cumulative slip distribution along 255 faults with lengths ranging from 0.3 to 60 km. Faults exhibiting the elliptical or "bell-shaped" slip profiles predicted by simple linear elastic fracture mechanics or elastic-plastic theories are rare. Most slip profiles are roughly linear for more than half of their length, with overall slopes always <0.035. For the dominant population of NW striking faults and fault systems longer than 2 km, the slip profiles are asymmetric, with slip being maximum near the eastern ends of the profiles where it drops abruptly to zero, whereas slip decreases roughly linearly and tapers in the direction of overall Aden rift propagation. At a more detailed level, most faults appear to be composed of distinct, shorter subfaults or segments, whose slip profiles, while different from one to the next, combine to produce the roughly linear overall slip decrease along the entire fault. On a larger scale, faults cluster into kinematically coupled systems, along which the slip on any scale individual fault or fault system complements that of its neighbors, so that the total slip of the whole system is roughly linearly related to its length, with an average slope again <0.035. We discuss the origin of these quasilinear, asymmetric profiles in terms of "initiation points" where slip starts, and "barriers" where fault propagation is arrested. In the absence of a barrier, slip apparently extends with a roughly linear profile, tapered in the direction of fault propagation.

Surface Rupture and Slip Distribution Resulting from the 2013 M7.7 Balochistan, Pakistan Earthquake

NASA Astrophysics Data System (ADS)

Reitman, N. G.; Gold, R. D.; Briggs, R. W.; Barnhart, W. D.; Hayes, G. P.

2014-12-01

The 24 September 2013 M7.7 earthquake in Balochistan, Pakistan, produced a ~200 km long left-lateral strike-slip surface rupture along a portion of the Hoshab fault, a moderately dipping (45-75º) structure in the Makran accretionary prism. The rupture is remarkably continuous and crosses only two (0.7 and 1.5 km wide) step-overs along its arcuate path through southern Pakistan. Displacements are dominantly strike-slip, with a minor component of reverse motion. We remotely mapped the surface rupture at 1:5,000 scale and measured displacements using high resolution (0.5 m) pre- and post-event satellite imagery. We mapped 295 laterally faulted stream channels, terrace margins, and roads to quantify near-field displacement proximal (±10 m) to the rupture trace. The maximum near-field left-lateral offset is 15±2 m (average of ~7 m). Additionally, we used pre-event imagery to digitize 254 unique landforms in the "medium-field" (~100-200 m from the rupture) and then measured their displacements compared to the post-event imagery. At this scale, maximum left-lateral offset approaches 17 m (average of ~8.5 m). The width (extent of observed surface faulting) of the rupture zone varies from ~1 m to 3.7 km. Near- and medium-field offsets show similar slip distributions that are inversely correlated with the width of the fault zone at the surface (larger offsets correspond to narrow fault zones). The medium-field offset is usually greater than the near-field offset. The along-strike surface slip distribution is highly variable, similar to the slip distributions documented for the 2002 Denali M7.9 earthquake and 2001 Kunlun M7.8 earthquake, although the Pakistan offsets are larger in magnitude. The 2013 Pakistan earthquake ranks among the largest documented continental strike-slip displacements, possibly second only to the 18+ m surface displacements attributed to the 1855 Wairarapa M~8.1 earthquake.

Refining fault slip rates using multiple displaced terrace risers-An example from the Honey Lake fault, NE California, USA

NASA Astrophysics Data System (ADS)

Gold, Ryan D.; Briggs, Richard W.; Crone, Anthony J.; DuRoss, Christopher B.

2017-11-01

Faulted terrace risers are semi-planar features commonly used to constrain Quaternary slip rates along strike-slip faults. These landforms are difficult to date directly and therefore their ages are commonly bracketed by age estimates of the adjacent upper and lower terrace surfaces. However, substantial differences in the ages of the upper and lower terrace surfaces (a factor of 2.4 difference observed globally) produce large uncertainties in the slip-rate estimate. In this investigation, we explore how the full range of displacements and bounding ages from multiple faulted terrace risers can be combined to yield a more accurate fault slip rate. We use 0.25-m cell size digital terrain models derived from airborne lidar data to analyze three sites where terrace risers are offset right-laterally by the Honey Lake fault in NE California, USA. We use ages for locally extensive subhorizontal surfaces to bracket the time of riser formation: an upper surface is the bed of abandoned Lake Lahontan having an age of 15.8 ± 0.6 ka and a lower surface is a fluvial terrace abandoned at 4.7 ± 0.1 ka. We estimate lateral offsets of the risers ranging between 6.6 and 28.3 m (median values), a greater than fourfold difference in values. The amount of offset corresponds to the riser's position relative to modern stream meanders: the smallest offset is in a meander cutbank position, whereas the larger offsets are in straight channel or meander point-bar positions. Taken in isolation, the individual terrace-riser offsets yield slip rates ranging from 0.3 to 7.1 mm/a. However, when the offset values are collectively assessed in a probabilistic framework, we find that a uniform (linear) slip rate of 1.6 mm/a (1.4-1.9 mm/a at 95% confidence) can satisfy the data, within their respective uncertainties. This investigation demonstrates that integrating observations of multiple offset elements (crest, midpoint, and base) from numerous faulted and dated terrace risers at closely spaced sites can refine slip-rate estimates on strike-slip faults.

Refining fault slip rates using multiple displaced terrace risers—An example from the Honey Lake fault, NE California, USA

USGS Publications Warehouse

Gold, Ryan D.; Briggs, Richard; Crone, Anthony J.; Duross, Christopher

2017-01-01

Faulted terrace risers are semi-planar features commonly used to constrain Quaternary slip rates along strike-slip faults. These landforms are difficult to date directly and therefore their ages are commonly bracketed by age estimates of the adjacent upper and lower terrace surfaces. However, substantial differences in the ages of the upper and lower terrace surfaces (a factor of 2.4 difference observed globally) produce large uncertainties in the slip-rate estimate. In this investigation, we explore how the full range of displacements and bounding ages from multiple faulted terrace risers can be combined to yield a more accurate fault slip rate. We use 0.25-m cell size digital terrain models derived from airborne lidar data to analyze three sites where terrace risers are offset right-laterally by the Honey Lake fault in NE California, USA. We use ages for locally extensive subhorizontal surfaces to bracket the time of riser formation: an upper surface is the bed of abandoned Lake Lahontan having an age of 15.8 ± 0.6 ka and a lower surface is a fluvial terrace abandoned at 4.7 ± 0.1 ka. We estimate lateral offsets of the risers ranging between 6.6 and 28.3 m (median values), a greater than fourfold difference in values. The amount of offset corresponds to the riser's position relative to modern stream meanders: the smallest offset is in a meander cutbank position, whereas the larger offsets are in straight channel or meander point-bar positions. Taken in isolation, the individual terrace-riser offsets yield slip rates ranging from 0.3 to 7.1 mm/a. However, when the offset values are collectively assessed in a probabilistic framework, we find that a uniform (linear) slip rate of 1.6 mm/a (1.4–1.9 mm/a at 95% confidence) can satisfy the data, within their respective uncertainties. This investigation demonstrates that integrating observations of multiple offset elements (crest, midpoint, and base) from numerous faulted and dated terrace risers at closely spaced sites can refine slip-rate estimates on strike-slip faults.

Geodetic slip model of the 3 September 2016 Mw 5.8 Pawnee, Oklahoma, earthquake: Evidence for fault‐zone collapse

USGS Publications Warehouse

Pollitz, Fred; Wicks, Charles W.; Schoenball, Martin; Ellsworth, William L.; Murray, Mark

2017-01-01

The 3 September 2016 Mw 5.8 Pawnee earthquake in northern Oklahoma is the largest earthquake ever recorded in Oklahoma. The coseismic deformation was measured with both Interferometric Synthetic Aperture Radar and Global Positioning System (GPS), with measureable signals of order 1 cm and 1 mm, respectively. We derive a coseismic slip model from Sentinel‐1A and Radarsat 2 interferograms and GPS static offsets, dominated by distributed left‐lateral strike slip on a primary west‐northwest–east‐southeast‐trending subvertical plane, whereas strike slip is concentrated near the hypocenter (5.6 km depth), with maximum slip of ∼1  m located slightly east and down‐dip of the hypocenter. Based on systematic misfits of observed interferogram line‐of‐sight (LoS) displacements, with LoS based on shear‐dislocation models, a few decimeters of fault‐zone collapse are inferred in the hypocentral region where coseismic slip was the largest. This may represent the postseismic migration of large volumes of fluid away from the high‐slip areas, made possible by the creation of a temporary high‐permeability damage zone around the fault.

Flower-strucutre deformation pattern of theTian Shan mountains as revealed by Late Quaternary geological and modern Geodesy slip rates

NASA Astrophysics Data System (ADS)

Wu, C.; Zhang, P.; Zheng, W.; Wang, H.; Zhang, Z.; Ren, Z.; Zheng, D.; Yu, J.; Wu, G.

2017-12-01

The deformation pattern and strain distribution of the Tian Shan is a hot issue.Previous studies mainly focus on the thrust-fold systems on both sides of Tian Shan, the strike-slip faults within the mountains are rarely reported. The understanding about the deformation characteristics of Tian Shan is not complete for lacking information of these strike-slip faults.Our studies show the NEE trending structures of Maidan fault and Nalati fault in the southwestern Tian Shan are all active during the Holence. These faults are characterized by sinistral strike-slip and thrust movement. The minimum average sinistral strike-slip rate of the Maidan fault is 1.07 ± 0.13 mm/yr. During the late Quaternary, the average shortening rate and sinistral strike-slip rate of the Nalati fault are 2.1 ±0.4 mm/yr and 2.56 ±0.25 mm/yr, respectively . In the interior of the Tian Shan area, two groups of strike-slip faults were developed. The NEE trending faults with sinistral strike-slipmovement, and the NWW trending faults with dextral strike-slip movement show the shape of "X"in geometrical structure. The piedmont thrust faults and the thrust strike-slip faults in the interior mountain constitute the tectonic framework of Tian Shan. Threegroups of active fault systems are the main seismogenic and geological structures, which control the current tectonic deformation pattern of Tian Shan (Figure 1). GPS observation data also showthe similar deformation characteristics with the geological results (Figures 2, 3). In addition to the crustal shortening, there is a certain strike-slip shear movement in the interior of the Tian Shan.The strike-slip rate defined by the geological and GPS data is approximately consistent with each other near the same longitude. We suggest the two groups of strike-slip faults in the interior of mountains is a set of conjugate structures. The whole Tian Shan forms a large flower-structure in a profile view. The complete tectonic deformation of the Tian Shan mountains consists ofthe shortening deformationof the N-S direction and the lateral extrusion of the E-W direction (Figure 2). The late Cenozoic deformation of the Tian Shan mountains is due to the northward subduction of Tarim Block. Although the activedeformation of the Tian Shan decrease eastward, the geological sturcutrein eastern Tian Shan is similar.

Mechanisms-based viscoplasticity: Theoretical approach and experimental validation for steel 304L

PubMed Central

Zubelewicz, Aleksander; Oliferuk, Wiera

2016-01-01

We propose a mechanisms-based viscoplasticity approach for metals and alloys. First, we derive a stochastic model for thermally-activated motion of dislocations and, then, introduce power-law flow rules. The overall plastic deformation includes local plastic slip events taken with an appropriate weight assigned to each angle of the plane misorientation from the direction of maximum shear stress. As deformation progresses, the material experiences successive reorganizations of the slip systems. The microstructural evolution causes that a portion of energy expended on plastic deformation is dissipated and the rest is stored in the defect structures. We show that the reorganizations are stable in a homogeneously deformed material. The concept is tested for steel 304L, where we reproduce experimentally obtained stress-strain responses, we construct the Frost-Ashby deformation map and predict the rate of the energy storage. The storage is assessed in terms of synchronized measurements of temperature and displacement distributions on the specimen surface during tensile loading. PMID:27026209

Washington Play Fairway Analysis Geothermal GIS Data

DOE Data Explorer

Corina Forson

2015-12-15

This file contains file geodatabases of the Mount St. Helens seismic zone (MSHSZ), Wind River valley (WRV) and Mount Baker (MB) geothermal play-fairway sites in the Washington Cascades. The geodatabases include input data (feature classes) and output rasters (generated from modeling and interpolation) from the geothermal play-fairway in Washington State, USA. These data were gathered and modeled to provide an estimate of the heat and permeability potential within the play-fairways based on: mapped volcanic vents, hot springs and fumaroles, geothermometry, intrusive rocks, temperature-gradient wells, slip tendency, dilation tendency, displacement, displacement gradient, max coulomb shear stress, sigma 3, maximum shear strain rate, and dilational strain rate at 200m and 3 km depth. In addition this file contains layer files for each of the output rasters. For details on the areas of interest please see the 'WA_State_Play_Fairway_Phase_1_Technical_Report' in the download package. This submission also includes a file with the geothermal favorability of the Washington Cascade Range based off of an earlier statewide assessment. Additionally, within this file there are the maximum shear and dilational strain rate rasters for all of Washington State.

Micro-Scale Thermoacoustics

NASA Astrophysics Data System (ADS)

Offner, Avshalom; Ramon, Guy Z.

2016-11-01

Thermoacoustic phenomena - conversion of heat to acoustic oscillations - may be harnessed for construction of reliable, practically maintenance-free engines and heat pumps. Specifically, miniaturization of thermoacoustic devices holds great promise for cooling of micro-electronic components. However, as devices size is pushed down to micro-meter scale it is expected that non-negligible slip effects will exist at the solid-fluid interface. Accordingly, new theoretical models for thermoacoustic engines and heat pumps were derived, accounting for a slip boundary condition. These models are essential for the design process of micro-scale thermoacoustic devices that will operate under ultrasonic frequencies. Stability curves for engines - representing the onset of self-sustained oscillations - were calculated with both no-slip and slip boundary conditions, revealing improvement in the performance of engines with slip at the resonance frequency range applicable for micro-scale devices. Maximum achievable temperature differences curves for thermoacoustic heat pumps were calculated, revealing the negative effect of slip on the ability to pump heat up a temperature gradient. The authors acknowledge the support from the Nancy and Stephen Grand Technion Energy Program (GTEP).

Numerical Models of Stopping Ruptures on a Bimaterial Interface

NASA Astrophysics Data System (ADS)

Rubin, A. M.; Ampuero, J.

2003-12-01

Using a cross-correlation earthquake relocation technique, Rubin and Gillard (2000) and Rubin (2002) found that the nearest aftershocks of microearthquakes on the San Andreas fault were much more likely (by a ratio of nearly 3:1) to occur to the NW of the mainshock than to the SE. They attributed this asymmetry to the material contrast across the fault and the resulting dynamical reduction in normal stress near the rupture front propagating to the SE (the front moving in the direction of slip of the more compliant medium). Specifically, it was hypothesized that regions of the fault far enough from failure to resist this extra dynamical "kick" would be that much farther from failure once those dynamical stresses decayed. However, analytical (steady-state) models of propagating slip on a bimaterial interface (Weertman, 1980) show that, as with the static stress field, normal stress changes occur only behind the rupture front. The proposed explanation works most simply if the region ahead of the SE rupture front experiences a transient stress favorable for slip. In principal this stress transient could be associated with either rupture growth or arrest. To investigate this further, we ran 2-D numerical models of slip on a bimaterial interface with slip-weakening friction, using the code of Cochard and Rice (2000). The ruptures spontaneously accelerate to the generalized Rayleigh wave speed of the medium, when such exists. During this growth phase, large tensile stresses are indeed restricted to regions of large slip velocity behind the SE-propagating rupture front. Ahead of the rupture front the normal stresses are smaller and compressive. If the rupture front is stopped abruptly, the short-wavelength tensile stress pulse continues to propagate at roughly the same velocity. The above comments also apply in an anti-symmetric sense to the NW rupture front, although there the slip speeds and normal stress changes are lower. If the rupture is stopped by a more gradual reduction in the loading stress, the moving tensile pulse can spawn a decaying slip pulse at the SE front but not the NW. If this slip pulse marks the furthest extent of slip, the resulting static stress field is quite asymmetric even for a symmetric initial stress, lying on the failure envelope at the NW end of the rupture but well below it at the SE end. These results are at least permissive of the explanation proposed by Rubin and Gillard. For weaker slip pulses (due to any of a number of factors contributing to smaller maximum slip speeds), the furthest extent of slip near the SE rupture front can be driven by the stopping phase arriving from the NW end of the crack. Under such conditions the final stress field is more symmetric. We will be running models using heterogeneous stress fields to explore these questions further, and hope to use rate-and-state friction to investigate the observed temporal decay of the aftershock asymmetry.

Seismic slip on clay nano-foliation

NASA Astrophysics Data System (ADS)

Aretusini, Stefano; Plümper, Oliver; Spagnuolo, Elena; Di Toro, Giulio

2017-04-01

Deformation processes active at seismic slip rates (ca. 1 m/s) on smectite-rich slipping zones are not well understood, although they likely control the mechanical behaviour of: i) subduction zone faults affected by tsunamigenic earthquakes and seismic surface rupturing, and ii) landslide decollements. Here we present a set of rotary experiments performed on water-dampened 2 mm thick clay-rich (70% wt. smectite and 30% wt. opal) gouge layers sheared at slip rates V ranging from 0.01 to 1.5 m/s, for 3 m of displacement under 5 MPa normal stress. Microstructural analyses were conducted on pre- and post-sheared gouges using focused ion beam scanning electron and transmission electron microscopy. All sheared gouges were slip weakening in the first 0.1 m of displacement, with friction coefficient decreasing from 0.4-0.3 to 0.1-0.05. Then, with progressive slip, gouges evolved to slip-strengthening (final friction coefficient of 0.47-0.35) at V ≤0.1 m/s and slip-neutral (final friction of 0.05) at V=1.5 m/s. Despite the large difference in the imposed slip rate and frictional behaviour, the slipping zone always consisted of a nano-foliation defined by sub-micrometric smectite crystals wrapping opal grains. The microstructural differences were (1) the thickness of the slipping zone which decreased from 1.5 mm at V≤0.1 m/s to 0.15 mm at V=1.5 m/s, and (2) the structure of the foliated fabric, which was S/C'-type at V≤0.1 m/s and anastomosing-type at V=1.5 m/s. The presence of a similar nano-foliation in all the smectite-rich wet gouges suggests the activation of similar frictional processes, most likely grain boundary and interlayer frictional sliding aided by water films, operating from sub-seismic to seismic strain rates ( 10-10000 1/s). Water films on crystal boundaries and interlayers possibly control the micro- and nano-mechanics of smectite deformation, therefore influencing the bulk frictional behaviour during seismic slip.

Holocene geologic slip rate for the Banning strand of the southern San Andreas Fault, southern California

USGS Publications Warehouse

Gold, Peter O.; Behr, Whitney M.; Rood, Dylan; Sharp, Warren D.; Rockwell, Thomas; Kendrick, Katherine J.; Salin, Aaron

2015-01-01

Northwest directed slip from the southern San Andreas Fault is transferred to the Mission Creek, Banning, and Garnet Hill fault strands in the northwestern Coachella Valley. How slip is partitioned between these three faults is critical to southern California seismic hazard estimates but is poorly understood. In this paper, we report the first slip rate measured for the Banning fault strand. We constrain the depositional age of an alluvial fan offset 25 ± 5 m from its source by the Banning strand to between 5.1 ± 0.4 ka (95% confidence interval (CI)) and 6.4 + 3.7/−2.1 ka (95% CI) using U-series dating of pedogenic carbonate clast coatings and 10Be cosmogenic nuclide exposure dating of surface clasts. We calculate a Holocene geologic slip rate for the Banning strand of 3.9 + 2.3/−1.6 mm/yr (median, 95% CI) to 4.9 + 1.0/−0.9 mm/yr (median, 95% CI). This rate represents only 25–35% of the total slip accommodated by this section of the southern San Andreas Fault, suggesting a model in which slip is less concentrated on the Banning strand than previously thought. In rejecting the possibility that the Banning strand is the dominant structure, our results highlight an even greater need for slip rate and paleoseismic measurements along faults in the northwestern Coachella Valley in order to test the validity of current earthquake hazard models. In addition, our comparison of ages measured with U-series and 10Be exposure dating demonstrates the importance of using multiple geochronometers when estimating the depositional age of alluvial landforms.

Evolving geometrical heterogeneities of fault trace data

NASA Astrophysics Data System (ADS)

Wechsler, Neta; Ben-Zion, Yehuda; Christofferson, Shari

2010-08-01

We perform a systematic comparative analysis of geometrical fault zone heterogeneities using derived measures from digitized fault maps that are not very sensitive to mapping resolution. We employ the digital GIS map of California faults (version 2.0) and analyse the surface traces of active strike-slip fault zones with evidence of Quaternary and historic movements. Each fault zone is broken into segments that are defined as a continuous length of fault bounded by changes of angle larger than 1°. Measurements of the orientations and lengths of fault zone segments are used to calculate the mean direction and misalignment of each fault zone from the local plate motion direction, and to define several quantities that represent the fault zone disorder. These include circular standard deviation and circular standard error of segments, orientation of long and short segments with respect to the mean direction, and normal separation distances of fault segments. We examine the correlations between various calculated parameters of fault zone disorder and the following three potential controlling variables: cumulative slip, slip rate and fault zone misalignment from the plate motion direction. The analysis indicates that the circular standard deviation and circular standard error of segments decrease overall with increasing cumulative slip and increasing slip rate of the fault zones. The results imply that the circular standard deviation and error, quantifying the range or dispersion in the data, provide effective measures of the fault zone disorder, and that the cumulative slip and slip rate (or more generally slip rate normalized by healing rate) represent the fault zone maturity. The fault zone misalignment from plate motion direction does not seem to play a major role in controlling the fault trace heterogeneities. The frequency-size statistics of fault segment lengths can be fitted well by an exponential function over the entire range of observations.

Secular Variation in Slip (Invited)

NASA Astrophysics Data System (ADS)

Cowgill, E.; Gold, R. D.

2010-12-01

Faults show temporal variations in slip rate at time scales ranging from the hours following a major rupture to the millions of years over which plate boundaries reorganize. One such behavior is secular variation in slip (SVS), which we define as a pulse of accelerated strain release along a single fault that occurs at a frequency that is > 1 order of magnitude longer than the recurrence interval of earthquakes within the pulse. Although numerous mechanical models have been proposed to explain SVS, it has proven much harder to measure long (5-500 kyr) records of fault displacement as a function of time. Such fault-slip histories may be obtained from morphochronologic data, which are measurements of offset and age obtained from faulted landforms. Here we describe slip-history modeling of morphochronologic data and show how this method holds promise for obtaining long records of fault slip. In detail we place SVS in the context of other types of time-varying fault-slip phenomena, explain the importance of measuring fault-slip histories, summarize models proposed to explain SVS, review current approaches for measuring SVS in the geologic record, and illustrate the slip-history modeling approach we advocate here using data from the active, left-slip Altyn Tagh fault in NW Tibet. In addition to SVS, other types of temporal variation in fault slip include post-seismic transients, discrepancies between geologic slip rates and those derived from geodetic and/or paleoseismic data, and single changes in slip rate resulting from plate reorganization. Investigating secular variation in slip is important for advancing understanding of long-term continental deformation, fault mechanics, and seismic risk. Mechanical models producing such behavior include self-driven mode switching, changes in pore-fluid pressure, viscoelasticity, postseismic reloading, and changes in local surface loads (e.g., ice sheets, large lakes, etc.) among others. However, a key problem in testing these models is the paucity of long records of fault slip. Paleoseismic data are unlikely to yield such histories because measurements of the slip associated with each event are generally unavailable and long records require large accumulated offsets, which can result in structural duplication or omission of the stratigraphic records of events. In contrast, morphochronologic data capture both the age and offset of individual piercing points, although this approach generally does not resolve individual earthquake events. Because the uncertainties in both age and offset are generally large (5-15%) for individual markers, SVS is best resolved by obtaining suites of such measurements, in which case the errors can be used to reduce the range of slip histories common to all such data points. A suite of such data from the central Altyn Tagh fault reveals a pulse of accelerated strain release in the mid Holocene, with ~20 m of slip being released from ~6.7 to ~5.9 ka at a short-term rate (~28 mm/yr) that is 3 times greater than the average rate (~9 mm/yr). We interpret this pulse to represent a cluster of two to six, Mw > 7.2 earthquakes. To our knowledge, this is the first possible earthquake cluster detected using morphochronologic techniques.

Lateral offsets on surveyed cultural features resulting from the 1999 İzmit and Düzce earthquakes, Turkey

USGS Publications Warehouse

Rockwell, Thomas K.; Lindvall, Scott; Dawson, Tim; Langridge, Rob; Lettis, William; Klinger, Yann

2002-01-01

Surveys of multiple tree lines within groves of poplar trees, planted in straight lines across the fault prior to the earthquake, show surprisingly large lateral variations. In one grove, slip increases by nearly 1.8 m, or 35% of the maximum measured value, over a lateral distance of nearly 100 m. This and other observations along the 1999 ruptures suggest that the lateral variability of slip observed from displaced geomorphic features in many earthquakes of the past may represent a combination of (1) actual differences in slip at the surface and (2) the difficulty in recognizing distributed nonbrittle deformation.

How Long Is Long Enough? Estimation of Slip-Rate and Earthquake Recurrence Interval on a Simple Plate-Boundary Fault Using 3D Paleoseismic Trenching

NASA Astrophysics Data System (ADS)

Wechsler, N.; Rockwell, T. K.; Klinger, Y.; Agnon, A.; Marco, S.

2012-12-01

Models used to forecast future seismicity make fundamental assumptions about the behavior of faults and fault systems in the long term, but in many cases this long-term behavior is assumed using short-term and perhaps non-representative observations. The question arises - how long of a record is long enough to represent actual fault behavior, both in terms of recurrence of earthquakes and of moment release (aka slip-rate). We test earthquake recurrence and slip models via high-resolution three-dimensional trenching of the Beteiha (Bet-Zayda) site on the Dead Sea Transform (DST) in northern Israel. We extend the earthquake history of this simple plate boundary fault to establish slip rate for the past 3-4kyr, to determine the amount of slip per event and to study the fundamental behavior, thereby testing competing rupture models (characteristic, slip-patch, slip-loading, and Gutenberg Richter type distribution). To this end we opened more than 900m of trenches, mapped 8 buried channels and dated more than 80 radiocarbon samples. By mapping buried channels, offset by the DST on both sides of the fault, we obtained for each an estimate of displacement. Coupled with fault crossing trenches to determine event history, we construct earthquake and slip history for the fault for the past 2kyr. We observe evidence for a total of 9-10 surface-rupturing earthquakes with varying offset amounts. 6-7 events occurred in the 1st millennium, compared to just 2-3 in the 2nd millennium CE. From our observations it is clear that the fault is not behaving in a periodic fashion. A 4kyr old buried channel yields a slip rate of 3.5-4mm/yr, consistent with GPS rates for this segment. Yet in spite of the apparent agreement between GPS, Pleistocene to present slip rate, and the lifetime rate of the DST, the past 800-1000 year period appears deficit in strain release. Thus, in terms of moment release, most of the fault has remained locked and is accumulating elastic strain. In contrast, the preceding 1200 years or so experienced a spate of earthquake activity, with large events along the Jordan Valley segment alone in 31 BCE, 363, 749, and 1033 CE. Thus, the return period appears to vary by a factor of two to four during the historical period in the Jordan Valley as well as at our site. The Beteiha site seems to be affected by both its southern and northern neighboring segments, and there is tentative evidence that earthquakes nucleating in the Jordan Valley (e.g. 749 CE) can rupture through the Galilee step-over to the south of Beteiha, or trigger a smaller event on the Jordan Gorge segment, in which case the historical record will tend to amalgamate any evidence for it into one large event. We offer a model of earthquake slip for this segment, in which the overall slip rate remains constant, yet differing earthquake sizes can occur, depending on the segment from which they originated and the time since the last large event. The rate of earthquake production in this model does not produce a time predictable pattern over a period of 2kyr, and the slip rate varies between the 1st and 2nd millennia CE, as a result of the interplay between coalescing fault segments to the north.

Long-term slip rate of the southern San Andreas Fault, from 10Be-26Al surface exposure dating of an offset alluvial fan

DOE Office of Scientific and Technical Information (OSTI.GOV)

der Woerd, J v; Klinger, Y; Sieh, K

We determine the long-term slip rate of the southern San Andreas Fault in the southeastern Indio Hills using {sup 10}Be and {sup 26}Al isotopes to date an offset alluvial fan surface. Field mapping complemented with topographic data, air photos and satellite images allow to precisely determine piercing points across the fault zone that are used to measure an offset of 565 {+-} 80 m. A total of twenty-six quartz-rich cobbles from three different fan surfaces were collected and dated. The tight cluster of nuclide concentrations from 19 samples out of 20 from the offset fan surface implies a simple exposuremore » history, negligible prior exposure and erosion, and yield an age of 35.5 {+-} 2.5 ka. The long-term slip rate of the San Andreas Fault south of Biskra Palms is thus 15.9 {+-} 3.4 mm/yr. This rate is about 10 mm/yr slower than geological (0-14 ka) and short-term geodetic estimates for this part of the San Andreas Fault implying changes in slip rate or in faulting behavior. This result puts new constraints on the slip rate of the San Jacinto and on the Eastern California Shear Zone for the last 35 ka. Our study shows that more sites along the major faults of southern California need to be targeted to better constrain the slip-rates over different time scales.« less

Southeastward increase of the late Quaternary slip-rate of the Xianshuihe fault, eastern Tibet. Geodynamic and seismic hazard implications

NASA Astrophysics Data System (ADS)

Bai, Mingkun; Chevalier, Marie-Luce; Pan, Jiawei; Replumaz, Anne; Leloup, Philippe Hervé; Métois, Marianne; Li, Haibing

2018-03-01

The left-lateral strike-slip Xianshuihe fault system located in the eastern Tibetan Plateau is considered as one of the most tectonically active intra-continental fault system in China, along which more than 20 M > 6.5 and more than 10 M > 7 earthquakes occurred since 1700. Therefore, studying its activity, especially its slip rate at different time scales, is essential to evaluate the regional earthquake hazard. Here, we focus on the central segment of the Xianshuihe fault system, where the Xianshuihe fault near Kangding city splays into three branches: the Selaha, Yalahe and Zheduotang faults. In this paper we use precise dating together with precise field measurements of offsets to re-estimate the slip rate of the fault that was suggested without precise age constraints. We studied three sites where the active Selaha fault cuts and left-laterally offsets moraine crests and levees. We measured horizontal offsets of 96 ± 20 m at Tagong levees (TG), 240 ± 15 m at Selaha moraine (SLH) and 80 ± 5 m at Yangjiagou moraine (YJG). Using 10Be cosmogenic dating, we determined abandonment ages at Tagong, Selaha and Yangjiagou of 12.5 (+ 2.5 / - 2.2) ka, 22 ± 2 ka, and 18 ± 2 ka, respectively. By matching the emplacement age of the moraines or levees with their offsets, we obtain late Quaternary horizontal average slip-rates of 7.6 (+ 2.3 / - 1.9) mm/yr at TG and 10.7 (+ 1.3 / - 1.1) mm/yr at SLH, i.e., 5.7-12 mm/yr or between 9.6 and 9.9 mm/yr assuming that the slip rate should be constant between the nearby TG and SLH sites. At YJG, we obtain a lower slip rate of 4.4 ± 0.5 mm/yr, most likely because the parallel Zheduotang fault shares the slip rate at this longitude, therefore suggesting a ∼5 mm/yr slip rate along the Zheduotang fault. The ∼10 mm/yr late Quaternary rate along the Xianshuihe fault is higher than that along the Ganzi fault to the NW (6-8 mm/yr). This appears to be linked to the existence of the Longriba fault system that separates the Longmenshan and Bayan Har blocks north of the Xianshuihe fault system. A higher slip rate along the short (∼60 km) and discontinuous Selaha fault compared to that along the long (∼300 km) and linear Ganzi fault suggests a high hazard for a M > 6 earthquake in the Kangding area in the near future, which could devastate that densely populated city.

Holocene slip rate for the central Altyn Tagh Fault: Preliminary results from the Tuzidun site based on 14C and 10Be dating of a displaced fluvial terrace riser.

NASA Astrophysics Data System (ADS)

Gold, R. D.; Cowgill, E. S.; Arrowsmith, R.; Muretta, M.; Gosse, J.; Chen, X.; Wang, X.

2007-12-01

The active, left-slip Altyn Tagh Fault (ATF) defines the northern boundary of the Tibetan Plateau and is among the world's longest intracontinental strike-slip faults. Despite a decade of concentrated work, the Holocene slip rate for the central ATF is still disputed, with millennial slip rates derived from faulted landforms ranging from 9 to 27 mm/yr. To address this factor-of-three difference, we are investigating a new slip-rate site near Tuzidun (37.73N, 86.72E) along the Cherchen He reach of the fault. The new site is situated where a south-flowing, ephemeral stream channel crosses the N70E-striking, active trace of the ATF. This channel is flanked by a set of inset fluvial terraces along its eastern bank. North of the ATF, these terraces include both a younger/lower T1 tread and an older/higher T2 terrace, which are vertically separated by an intervening T2/T1 riser. South of the fault, the stream is inset into an alluvial fan, F1. The F1 fan is separated from the higher, T2 fluvial terrace tread to the east, by the T2/F1 riser. Our neotectonic mapping and survey data indicate that the T2/F1 riser on the south/downstream side of the ATF and the T2/T1 riser on the north/upstream side have been displaced from one another by left slip along the ATF. The present separation between these riser segments is ~56 m, though lateral erosion of the riser may have diminished the true offset. To account for this possibility, we have developed three end-member reconstructions that yield offsets ranging from 56 to105 m. Ongoing geochronologic and geomorphic analyses are designed further limit the range of possible displacements. Preliminary age analyses from the Tuzidun site include 22 new radiocarbon dates from buried organic materials and 7 analyses of 10Be concentration in quartz extracted from amalgamated samples of terrace conglomerates. The 14C analyses are from samples collected from within the T2 tread on both sides of the ATF and from loess deposits that cap the downstream T2/F1 riser face. The 10Be analyses are from samples collected in two depth profiles, north and south of the ATF, dug into the T2 deposit at the crest of the displaced riser. The calibrated 14C dates and 10Be surface-exposure ages are compatible, and indicate that the surfaces at the crest and toe of the riser were abandoned at ~6 ka and ~4.4 ka, respectively. To bracket the millennial slip rate at this site, we consider three end-member reconstructions. The first is an upper-terrace reconstruction, in which the riser started recording displacement as soon as the upper-terrace, T2, was abandoned, providing a minimum constraint on the slip rate of ~9 mm/yr since ~6 ka. An intermediate interpretation is a lower-terrace reconstruction, in which the riser accumulated no displacement until the lower surface, F1, was abandoned, yielding a slip rate of ~13 mm/yr since ~4.4 ka. The final reconstruction is one in which erosion of the upstream T2 surface, prior to T1/F1 deposition, diminished the present-day observed offset. In this case, up to 105 m of displacement has occurred since abandonment of the T2 surface, which permits a slip rate as high as ~18 mm/yr since ~6 ka. The new slip rate of 9-18 mm/yr for the Tuzidun site is consistent with our preliminary results from three additional slip-rate sites along the central ATF, and taken together, provides an upper limit of 18 mm/yr for the Holocene slip rate along this reach of the fault.

Vitesses de glissement à long terme et dislocations cosismiques caractéristiques : clés du fonctionnement des failles actives et de l'aléa sismique

NASA Astrophysics Data System (ADS)

Tapponnier, Paul; Ryerson, Frederick James; Van der Woerd, Jerome; Mériaux, Anne-Sophie; Lasserre, Cécile

2001-11-01

Over periods of thousands of years, active faults tend to slip at constant rates. Pioneer studies of large Asian faults show that cosmogenic radionuclides ( 10Be, 26Al) provide an unparalleled tool to date surface features, whose offsets yield the longest records of recent cumulative movement. The technique is thus uniquely suited to determine long-term (10-100 ka) slip rates. Such rates, combined with coseismic slip-amounts, can give access to recurrence times of earthquakes of similar sizes. Landform dating - morphochronology - is therefore essential to understand fault-behaviour, evaluate seismic hazard, and build physical earthquake models. It is irreplaceable because long-term slip-rates on interacting faults need not coincide with GPS-derived, interseismic rates, and can be difficult to obtain from paleo-seismological trenching.

Slow Slip and Earthquake Nucleation in Meter-Scale Laboratory Experiments

NASA Astrophysics Data System (ADS)

Mclaskey, G.

2017-12-01

The initiation of dynamic rupture is thought to be preceded by a quasistatic nucleation phase. Observations of recent earthquakes sometimes support this by illuminating slow slip and foreshocks in the vicinity of the eventual hypocenter. I describe laboratory earthquake experiments conducted on two large-scale loading machines at Cornell University that provide insight into the way earthquake nucleation varies with normal stress, healing time, and loading rate. The larger of the two machines accommodates a 3 m long granite sample, and when loaded to 7 MPa stress levels, we observe dynamic rupture events that are preceded by a measureable nucleation zone with dimensions on the order of 1 m. The smaller machine accommodates a 0.76 m sample that is roughly the same size as the nucleation zone. On this machine, small variations in nucleation properties result in measurable differences in slip events, and we generate both dynamic rupture events (> 0.1 m/s slip rates) and slow slip events ( 0.001 to 30 mm/s slip rates). Slow events occur when instability cannot fully nucleate before reaching the sample ends. Dynamic events occur after long healing times or abrupt increases in loading rate which suggests that these factors shrink the spatial and temporal extents of the nucleation zone. Arrays of slip, strain, and ground motion sensors installed on the sample allow us to quantify seismic coupling and study details of premonitory slip and afterslip. The slow slip events we observe are primarily aseismic (less than 1% of the seismic coupling of faster events) and produce swarms of very small M -6 to M -8 events. These mechanical and seismic interactions suggest that faults with transitional behavior—where creep, small earthquakes, and tremor are often observed—could become seismically coupled if loaded rapidly, either by a slow slip front or dynamic rupture of an earthquake that nucleated elsewhere.

Effects of Bounded Fault on Seismic Radiation and Rupture Propagation

NASA Astrophysics Data System (ADS)

Weng, H.; Yang, H.

2016-12-01

It has been suggested that narrow rectangle fault may emit stopping phases that can largely affect seismic radiation and thus rupture propagation, e.g., generation of short-duration pulse-like ruptures. Here we investigate the effects of narrow along-dip rectangle fault (analogously to 2015 Nepal earthquake with 200 km * 40 km) on seismic radiation and rupture propagation through numerical modeling in the framework of the linear slip-weakening friction law. First, we found the critical slip-weakening distance Dc may largely affect the seismic radiation and other source parameters, such as rupture speed, final slip and stress drop. Fixing all other uniform parameters, decreasing Dc could decrease the duration time of slip rate and increase the peak slip rate, thus increase the seismic radiation energy spectrum of slip acceleration. In addition, smaller Dc could lead to larger rupture speed (close to S wave velocity), but smaller stress drop and final slip. The results show that Dc may control the efficiency of far-field radiation. Furthermore, the duration time of slip rate at locations close to boundaries is 1.5 - 4 s less than that in the center of the fault. Such boundary effect is especially remarkable for smaller Dc due to the smaller average duration time of slip rate, which could increase the high-frequency radiation energy and impede low-frequency component near the boundaries from the analysis of energy spectrum of slip acceleration. These results show high frequency energy tends to be radiated near the fault boundaries as long as Dc is small enough. In addition, ruptures are fragile and easy to self-arrest if the width of the seismogenic zone is very narrow. In other words, the sizes of nucleation zone need to be larger to initiate runaway ruptures. Our results show the critical sizes of nucleation zones increase as the widths of seismogenic zones decrease.

Surface rupture of the 2002 Denali fault, Alaska, earthquake and comparison with other strike-slip ruptures

USGS Publications Warehouse

Haeussler, Peter J.; Schwartz, D.P.; Dawson, T.E.; Stenner, Heidi D.; Lienkaemper, J.J.; Cinti, F.; Montone, Paola; Sherrod, B.; Craw, P.

2004-01-01

On 3 November 2002, an M7.9 earthquake produced 340 km of surface rupture on the Denali and two related faults in Alaska. The rupture proceeded from west to east and began with a 40-km-long break on a previously unknown thrust fault. Estimates of surface slip on this thrust are 3-6 m. Next came the principal surface break along ???218 km of the Denali fault. Right-lateral offsets averaged around 5 m and increased eastward to a maximum of nearly 9 m. The fault also ruptured beneath the trans-Alaska oil pipeline, which withstood almost 6 m of lateral offset. Finally, slip turned southeastward onto the Totschunda fault. Right-lateral offsets are up to 3 m, and the surface rupture is about 76 km long. This three-part rupture ranks among the longest strike-slip events of the past two centuries. The earthquake is typical when compared to other large earthquakes on major intracontinental strike-slip faults. ?? 2004, Earthquake Engineering Research Institute.

Constant Fault Slip-Rates Over Hundreds of Millenia Constrained By Deformed Quaternary Palaeoshorelines: the Vibo and Capo D'Orlando Faults, Southern Italy.

NASA Astrophysics Data System (ADS)

Meschis, M.; Roberts, G.; Robertson, J.; Houghton, S.; Briant, R. M.

2017-12-01

Whether slip-rates on active faults accumulated over multiple seismic events is constant or varying over tens to hundreds of millenia timescales is an open question that can be addressed through study of deformed Quaternary palaeoshorelines. It is important to know the answer so that one can judge whether shorter timescale measurements (e.g. Holocene palaeoseismology or decadal geodesy) are suitable for determining earthquake recurrence intervals for Probabilistic Seismic Hazard Assessment or more suitable for studying temporal earthquake clustering. We present results from the Vibo Fault and the Capo D'Orlando Fault, that lie within the deforming Calabrian Arc, which has experienced damaging seismic events such as the 1908 Messina Strait earthquake ( Mw 7) and the 1905 Capo Vaticano earthquake ( Mw 7). These normal faults deform uplifted Late Quaternary palaeoshorelines, which outcrop mainly within their hangingwalls, but also partially in their footwalls, showing that a regional subduction and mantle-related uplift outpaces local fault-related subsidence. Through (1) field and DEM-based mapping of palaeoshorelines, both up flights of successively higher, older inner edges, and along the strike of the faults, and (2) utilisation of synchronous correlation of non-uniformly-spaced inner edge elevations with non-uniformly spaced sea-level highstand ages, we show that slip-rates decrease towards fault tips and that slip-rates have remained constant since 340 ka (given the time resolution we obtain). The slip-rates for the Capo D'Orlando Fault and Vibo Fault are 0.61mm/yr and 1mm/yr respectively. We show that the along-strike gradients in slip-rate towards fault tips differ for the two faults hinting at fault interaction and also discuss this in terms of other regions of extension like the Gulf of Corinth, Greece, where slip-rate has been shown to change through time through the Quaternary. We make the point that slip-rates may change through time as fault systems grow and fault interaction changes due to geometrical effects.

Nucleation and triggering of earthquake slip: effect of periodic stresses

USGS Publications Warehouse

Dieterich, J.H.

1987-01-01

Results of stability analyses for spring and slider systems, with state variable constitutive properties, are applied to slip on embedded fault patches. Unstable slip may nucleate only if the slipping patch exceeds some minimum size. Subsequent to the onset of instability the earthquake slip may propagate well beyond the patch. It is proposed that the seismicity of a volume of the earth's crust is determined by the distribution of initial conditions on the population of fault patches that nucleate earthquake slip, and the loading history acting upon the volume. Patches with constitutive properties inferred from laboratory experiments are characterized by an interval of self-driven accelerating slip prior to instability, if initial stress exceeds a minimum threshold. This delayed instability of the patches provides an explanation for the occurrence of aftershocks and foreshocks including decay of earthquake rates by time-1. A population of patches subjected to loading with a periodic component results in periodic variation of the rate of occurrence of instabilities. The change of the rate of seismicity for a sinusoidal load is proportional to the amplitude of the periodic stress component and inversely proportional to both the normal stress acting on the fault patches and the constitutive parameter, A1, that controls the direct velocity dependence of fault slip. Values of A1 representative of laboratory experiments indicate that in a homogeneous crust, correlation of earthquake rates with earth tides should not be detectable at normal stresses in excess of about 8 MPa. Correlation of earthquakes with tides at higher normal stresses can be explained if there exist inhomogeneities that locally amplify the magnitude of the tidal stresses. Such amplification might occur near magma chambers or other soft inclusions in the crust and possibly near the ends of creeping fault segments if the creep or afterslip rates vary in response to tides. Observations of seismicity rate variations associated with seasonal fluctuations of reservoir levels appear to be consistent with the model. ?? 1987.

Holocene slip rate along the northern Kongur Shan extensional system: insights on the large pull-apart structure in the NE Pamir

NASA Astrophysics Data System (ADS)

Pan, J.; Li, H.; Chevalier, M.; Liu, D.; Sun, Z.; Pei, J.; Wu, F.; Xu, W.

2013-12-01

Located at the northwestern end of the Himalayan-Tibetan orogenic belt, the Kongur Shan extensional system (KES) is a significant tectonic unit in the Chinese Pamir. E-W extension of the KES accommodates deformation due to the India/Asia collision in this area. Cenozoic evolution of the KES has been extensively studied, whereas Late Quaternary deformation along the KES is still poorly constrained. Besides, whether the KES is the northern extension of the Karakorum fault is still debated. Well-preserved normal fault scarps are present all along the KES. Interpretation of satellite images as well as field investigation allowed us to map active normal faults and associated vertically offset geomorphological features along the KES. At one site along the northern Kongur Shan detachment fault, in the eastern Muji basin, a Holocene alluvial fan is vertically offset by the active fault. We measured the vertical displacement of the fan with total station, and collected quartz cobbles for cosmogenic nuclide 10Be dating. Combining the 5-7 m offset and the preliminary surface-exposure ages of ~2.7 ka, we obtain a Holocene vertical slip-rate of 1.8-2.6 mm/yr along the fault. This vertical slip-rate is comparable to the right-lateral horizontal-slip rate along the Muji fault (~4.5 mm/yr, which is the northern end of the KES. Our result is also similar to the Late Quaternary slip-rate derived along the KES around the Muztagh Ata as well as the Tashkurgan normal fault (1-3 mm/yr). Geometry, kinematics, and geomorphology of the KES combined with the compatible slip-rate between the right-lateral strike-slip Muji fault and the Kongur Shan normal fault indicate that the KES may be an elongated pull-apart basin formed between the EW-striking right-lateral strike-slip Muji fault and the NW-SE-striking Karakorum fault. This unique elongated pull-apart structure with long normal fault in the NS direction and relatively short strike-slip fault in the ~EW direction seems to still be in formation, with the Karakorum fault still propagating to the north.

Slip in Great Megathrust Earthquakes and its Relation to Crustal Structure as Revealed by Satellite Free-air Gravity

NASA Astrophysics Data System (ADS)

Wells, R. E.; Blakely, R. J.; Scholl, D.

2007-12-01

In 2003, Song and Simons and Wells et al. showed that approximately 70% of the moment released during past large, shallow subduction zone thrust earthquakes occurred beneath trench-parallel, free-air gravity lows outlining the deep-sea slope terrace and its basins. The authors suggested that the basin-centered, fore-arc gravity lows might be good predictors of high seismic slip in future earthquakes. Since 2001, ten megathrust earthquakes have occurred with magnitudes greater than Mw 7.7, including the giant, Mw 9.17 Sumatra earthquake of 2004. These earthquakes provide a robust test of the idea that seismic slip is focused beneath basin-centered gravity lows, and also the related ideas that the landward maximum gravity gradient marks the effective down-dip limit of large coseismic slip, and that intrabasin, transverse gravity highs are areas of lower slip. A compilation of seismic and geodetic slip inversions for the post-2001 earthquakes and new analyses of slip for the great Antofagasta, Jalisco, and Peru events in 1995 and 1996 indicate that more than 80% of the high-slip areas occur beneath deep-sea terrace gravity lows (DSTL), and that half of the earthquake asperities lie beneath fore-arc basins or local gravity lows. The maximum gravity gradient along the landward margin of the deep-sea terrace may mark the point where thicker overlying crust and higher temperatures on the megathrust limit the down dip extent of stick-slip behavior. Onland analogues are the mountain front of the Himalaya, which approximately marks the down-dip limit of large coseismic slip along the Main Frontal Thrust, and the front of the Taiwan Central Ranges, which coincides with the limit of slip during the 1999 Chi-Chi earthquake (Mw 7.6). In the up dip direction, coseismic slip may be partitioned onto splay faults in the wedge, as occurred in the 1964 Alaska earthquake. The observed pattern of greater slip at depth beneath fore arc basins is consistent with partitioning of slip up dip, especially if outer wedge materials deform more slowly, as suggested for parts of the 2004 Sumatra rupture. Along strike variations in fore-arc gravity also correlate with changing seismic behavior. At Cape Erimo on Hokkaido, three Mw 8+ earthquakes (1952, 1968, 2003) have occurred on either side of the gravity high that overlies the Cape, with little coseismic slip beneath the high. To the northeast, the deep-sea terrace gradually narrows, as does the rupture width of the great earthquakes, until off the central Kurile Islands, the terrace disappears and the arc gravity high occupies the fore-arc. The gravity high had been an historic seismic gap that was filled by the 2006 Kurile Island earthquake (Mw 8.3). Although the earthquake nucleated under the high, the slip occurred beneath the adjacent gravity low to the northeast. This might suggest the gravity highs are not likely sources of large seismic moment, at least in M8 earthquakes. In contrast, the main asperity associated with the 2005 Sumatra (Mw 8.7) earthquake was beneath the large gravity high of Nias Island. An alternative view is that the gravity highs are stronger asperities that only rupture in giant earthquakes. Globally, the coincidence of basin- centered coseismic slip with geologic evidence of sustained subsidence of the fore-arc suggests that subduction erosion is occurring in the seismogenic zone. Recent work off Chile, Colombia, Peru, and elsewhere shows that subduction erosion is an important process in many subduction zones.

Observing and modeling the spectrum of a slow slip event: Constraints on the scaling of slow slip and tremor

NASA Astrophysics Data System (ADS)

Hawthorne, J. C.; Bartlow, N. M.; Ghosh, A.

2017-12-01

We estimate the normalized moment rate spectrum of a slow slip event in Cascadia and then attempt to reproduce it. Our goal is to further assess whether a single physical mechanism could govern slow slip and tremor events, with durations that span 6 orders of magnitude, so we construct the spectrum by parameterizing a large slow slip event as the sum of a number of subevents with various durations. The spectrum estimate uses data from three sources: the GPS-based slip inversion of Bartlow et al (2011), PBO borehole strain measurements, and beamforming-based tremor moment estimates of Ghosh et al (2009). We find that at periods shorter than 1 day, the moment rate power spectrum decays as frequencyn, where n is between 0.7 and 1.4 when measured from strain and between 1.2 and 1.4 when inferred from tremor. The spectrum appears roughly flat at periods of 1 to 10 days, as both the 1-day-period strain and tremor data and the 6-day-period slip inversion data imply a moment rate power of 0.02 times the the total moment squared. We demonstrate one way to reproduce this spectrum: by constructing the large-scale slow slip event as the sum of a series of subevents. The shortest of these subevents could be interpreted as VLFEs or even LFEs, while longer subevents might represent the aseismic slip that drives rapid tremor reverals, streaks, or rapid tremor migrations. We pick the subevent magnitudes from a Gutenberg-Richter distribution and place the events randomly throughout a 30-day interval. Then we assign each subevent a duration that scales with its moment to a specified power. Finally, we create a moment rate function for each subevent and sum all of the moment rates. We compute the summed slow slip moment rate spectra with two approaches: a time-domain numerical computation and a frequency-domain analytical summation. Several sets of subevent parameters can allow the constructed slow slip event to match the observed spectrum. One allowable set of parameters is of particular interest: a b-value of 1 coupled with subevent durations that scale linearly with their moments, as suggested by previous observations of slow earthquakes (Ide et al, 2007). Our work thus lends further plausibility to the existence of a single family of slow earthquakes, possibly governed by a single physical mechanism.

Fault slip rates in the modern new madrid seismic zone

PubMed

Mueller; Champion; Guccione; Kelson

1999-11-05

Structural and geomorphic analysis of late Holocene sediments in the Lake County region of the New Madrid seismic zone indicates that they are deformed by fault-related folding above the blind Reelfoot thrust fault. The widths of narrow kink bands exposed in trenches were used to model the Reelfoot scarp as a forelimb on a fault-bend fold; this, coupled with the age of folded sediment, yields a slip rate on the blind thrust of 6.1 +/- 0.7 mm/year for the past 2300 +/- 100 years. An alternative method used structural relief across the scarp and the estimated dip of the underlying blind thrust to calculate a slip rate of 4.8 +/- 0.2 mm/year. Geometric relations suggest that the right lateral slip rate on the New Madrid seismic zone is 1.8 to 2.0 mm/year.

Interseismic Deformation due to Oblique India-Sunda Collision: Implications for the Arakan Sleeping Giant

NASA Astrophysics Data System (ADS)

Mallick, R.; Lindsey, E. O.; Feng, L.; Hubbard, J.; Hill, E.

2017-12-01

The northern extent of the collision of the Indian and Sunda plates occurs along the Arakan megathrust. This collision is oblique, and at least two large strike-slip faults, the Sagaing Fault and the Churachandpur-Mao Fault (CMF) accommodate part of this obliquity. The megathrust is conspicuous in its lack of notable interplate earthquakes in the instrumental catalogue; it has even been called aseismic by some authors and suggested not to accumulate any elastic strain. Nevertheless, geological evidence from the great 1762 Arakan earthquake suggests that the megathrust is capable of producing M 8 and possibly tsunamigenic events that can adversely affect the lives of many millions of people living in the region. We present for the first time a new dataset of GPS rates from the MIBB (Myanmar-India-Bangladesh-Bhutan) cGPS network (2011-present), which consists of region-wide east-west and north-south profiles. We use a Bayesian framework to explore the fault geometry (locking depth and fault dip) and relative plate motion that can reproduce the pattern of east-west convergence in both previously published and our own GPS data. We explore the individual contributions of the megathrust, CMF, Sagaing Fault, and block rotation to dextral shearing across the Indo-Burman ranges and further east. Our results suggest that the total convergence rate across the foldbelt is 14-18 mm/yr, while the total dextral shearing rate is 40 mm/yr. Rotation of the crustal sliver between the two major plates may explain some of this dextral motion, while reducing the strike-slip rates on the intervening faults. We show that given the current network geometry we are most sensitive to the location of maximum strain, i.e., the depth and distance from the trench below which the megathrust slides freely. Our results show that the megathrust is stably sliding below a depth of 30 km, but the seismogenic potential of the shallow megathrust and splay faults that possibly sole into the same system remain unresolved from purely geodetic data. Planned additional geodetic stations will help resolve the relative contribution of rotation and strike-slip faulting. Meanwhile, other forms of data such as paleoseismic observations may be necessary to determine how slip reaches the surface and better understand the seismic hazard.

Extended fault inversion with random slipmaps: a resolution test for the 2012 Mw 7.6 Nicoya, Costa Rica earthquake

NASA Astrophysics Data System (ADS)

López-Comino, José Ángel; Stich, Daniel; Ferreira, Ana M. G.; Morales, Jose

2015-09-01

Inversions for the full slip distribution of earthquakes provide detailed models of earthquake sources, but stability and non-uniqueness of the inversions is a major concern. The problem is underdetermined in any realistic setting, and significantly different slip distributions may translate to fairly similar seismograms. In such circumstances, inverting for a single best model may become overly dependent on the details of the procedure. Instead, we propose to perform extended fault inversion trough falsification. We generate a representative set of heterogeneous slipmaps, compute their forward predictions, and falsify inappropriate trial models that do not reproduce the data within a reasonable level of mismodelling. The remainder of surviving trial models forms our set of coequal solutions. The solution set may contain only members with similar slip distributions, or else uncover some fundamental ambiguity such as, for example, different patterns of main slip patches. For a feasibility study, we use teleseismic body wave recordings from the 2012 September 5 Nicoya, Costa Rica earthquake, although the inversion strategy can be applied to any type of seismic, geodetic or tsunami data for which we can handle the forward problem. We generate 10 000 pseudo-random, heterogeneous slip distributions assuming a von Karman autocorrelation function, keeping the rake angle, rupture velocity and slip velocity function fixed. The slip distribution of the 2012 Nicoya earthquake turns out to be relatively well constrained from 50 teleseismic waveforms. Two hundred fifty-two slip models with normalized L1-fit within 5 per cent from the global minimum from our solution set. They consistently show a single dominant slip patch around the hypocentre. Uncertainties are related to the details of the slip maximum, including the amount of peak slip (2-3.5 m), as well as the characteristics of peripheral slip below 1 m. Synthetic tests suggest that slip patterns such as Nicoya may be a fortunate case, while it may be more difficult to unambiguously reconstruct more distributed slip from teleseismic data.

The 2014 update to the National Seismic Hazard Model in California

USGS Publications Warehouse

Powers, Peter; Field, Edward H.

2015-01-01

The 2014 update to the U. S. Geological Survey National Seismic Hazard Model in California introduces a new earthquake rate model and new ground motion models (GMMs) that give rise to numerous changes to seismic hazard throughout the state. The updated earthquake rate model is the third version of the Uniform California Earthquake Rupture Forecast (UCERF3), wherein the rates of all ruptures are determined via a self-consistent inverse methodology. This approach accommodates multifault ruptures and reduces the overprediction of moderate earthquake rates exhibited by the previous model (UCERF2). UCERF3 introduces new faults, changes to slip or moment rates on existing faults, and adaptively smoothed gridded seismicity source models, all of which contribute to significant changes in hazard. New GMMs increase ground motion near large strike-slip faults and reduce hazard over dip-slip faults. The addition of very large strike-slip ruptures and decreased reverse fault rupture rates in UCERF3 further enhances these effects.

Holocene Geologic Slip Rate for the Banning Strand of the Southern San Andreas Fault near San Gorgonio Pass, Southern California

NASA Astrophysics Data System (ADS)

Gold, P. O.; Behr, W. M.; Rood, D. H.; Kendrick, K. J.; Rockwell, T. K.; Sharp, W. D.

2014-12-01

We present the first Holocene geologic slip rate for the Banning strand of the southern San Andreas Fault in southern California. The southern San Andreas Fault splays into the sub-parallel Banning and Mission Creek strands in the northwestern Coachella Valley, and although it has long been surmised that the Banning strand eventually accommodates the majority of displacement and transfers it into San Gorgonio Pass, until now it has been uncertain how slip is actually partitioned between these two fault strands. Our new slip rate measurement, critically located at the northwestern end of the Banning strand, overlaps within errors with the published rate for the southern San Andreas Fault measured at Biskra Palms Oasis. This indicates that the majority of southern San Andreas Fault displacement transfers from the southeastern Mission Creek strand northwest to the Banning strand and into San Gorgonio Pass. Our result corroborates the UCERF3 hazard model, and is consistent with most previous interpretations of how slip is partitioned between the Banning and Mission Creek fault strands. To measure this slip rate, we used B4 airborne LiDAR to identify the apex of an alluvial fan offset laterally 30 ± 5 m from its source. We calculated the depositional age of the fan using 10Be in-situ cosmogenic exposure dating of 5 cobbles and a depth profile. We calculated a most probable fan age of 4.0 +2.0/-1.6 ka (1σ) by combining the inheritance-corrected cobble ages assuming Gaussian uncertainty. However, the probability density function yielded a multi-peaked distribution, which we attribute to variable 10Be inheritance in the cobbles, so we favor the depth profile age of 2.2-3.6 ka. Combined, these measurements yield a late Holocene slip rate for the Banning strand of the southern San Andreas Fault of 11.1 +3.1/-3.3 mm/yr. This slip rate does not preclude possibility that some slip transfers north along the Mission Creek strand and the Garnet Hill fault, but it does confirm that the Banning strand has been the most probable rupture path for earthquakes nucleated on the southern San Andreas Fault over the past few thousand years, and is likely to remain so in the near future. This clarification of slip partitioning within the northwest Coachella Valley is timely given that the southern San Andreas Fault is considered overdue for a large earthquake.

2D Simulations of Earthquake Cycles at a Subduction Zone Based on a Rate and State Friction Law -Effects of Pore Fluid Pressure Changes-

NASA Astrophysics Data System (ADS)

Mitsui, Y.; Hirahara, K.

2006-12-01

There have been a lot of studies that simulate large earthquakes occurring quasi-periodically at a subduction zone, based on the laboratory-derived rate-and-state friction law [eg. Kato and Hirasawa (1997), Hirose and Hirahara (2002)]. All of them assume that pore fluid pressure in the fault zone is constant. However, in the fault zone, pore fluid pressure changes suddenly, due to coseismic pore dilatation [Marone (1990)] and thermal pressurization [Mase and Smith (1987)]. If pore fluid pressure drops and effective normal stress rises, fault slip is decelerated. Inversely, if pore fluid pressure rises and effective normal stress drops, fault slip is accelerated. The effect of pore fluid may cause slow slip events and low-frequency tremor [Kodaira et al. (2004), Shelly et al. (2006)]. For a simple spring model, how pore dilatation affects slip instability was investigated [Segall and Rice (1995), Sleep (1995)]. When the rate of the slip becomes high, pore dilatation occurs and pore pressure drops, and the rate of the slip is restrained. Then the inflow of pore fluid recovers the pore pressure. We execute 2D earthquake cycle simulations at a subduction zone, taking into account such changes of pore fluid pressure following Segall and Rice (1995), in addition to the numerical scheme in Kato and Hirasawa (1997). We do not adopt hydrostatic pore pressure but excess pore pressure for initial condition, because upflow of dehydrated water seems to exist at a subduction zone. In our model, pore fluid is confined to the fault damage zone and flows along the plate interface. The smaller the flow rate is, the later pore pressure recovers. Since effective normal stress keeps larger, the fault slip is decelerated and stress drop becomes smaller. Therefore the smaller flow rate along the fault zone leads to the shorter earthquake recurrence time. Thus, not only the frictional parameters and the subduction rate but also the fault zone permeability affects the recurrence time of earthquake cycle. Further, the existence of heterogeneity in the permeability along the plate interface can bring about other slip behaviors, such as slow slip events. Our simulations indicate that, in addition to the frictional parameters, the permeability within the fault damage zone is one of essential parameters, which controls the whole earthquake cycle.

Seismicity rate increases associated with slow slip episodes prior to the 2012 Mw 7.4 Ometepec earthquake

NASA Astrophysics Data System (ADS)

Colella, Harmony V.; Sit, Stefany M.; Brudzinski, Michael R.; Graham, Shannon E.; DeMets, Charles; Holtkamp, Stephen G.; Skoumal, Robert J.; Ghouse, Noorulann; Cabral-Cano, Enrique; Kostoglodov, Vladimir; Arciniega-Ceballos, Alejandra

2017-04-01

The March 20, 2012 Mw 7.4 Ometepec earthquake in the Oaxaca region of Southern Mexico provides a unique opportunity to examine whether subtle changes in seismicity, tectonic tremor, or slow slip can be observed prior to a large earthquake that may illuminate changes in stress or background slip rate. Continuous Global Positioning System (cGPS) data reveal a 5-month-long slow slip event (SSE) between ∼20 and 35 km depth that migrated toward and reached the vicinity of the mainshock a few weeks prior to the earthquake. Seismicity in Oaxaca is examined using single station tectonic tremor detection and multi-station waveform template matching of earthquake families. An increase in seismic activity, detected with template matching using aftershock waveforms, is only observed in the weeks prior to the mainshock in the region between the SSE and mainshock. In contrast, a SSE ∼15 months earlier occurred at ∼25-40 km depth and was primarily associated with an increase in tectonic tremor. Together, these observations indicate that in the Oaxaca region of Mexico shallower slow slip promotes elevated seismicity rates, and deeper slow slip promotes tectonic tremor. Results from this study add to a growing number of published accounts that indicate slow slip may be a common pre-earthquake signature.

New constraints on the late Quaternary slip rate and earthquake history of the Kalabagh fault from geomorphic mapping: Implications for slip rate and earthquake potential of the western Salt Range thrust

NASA Astrophysics Data System (ADS)

Madugo, C. M.; Meigs, A.; Ramzan, S.

2013-12-01

Whether the basal décollement ruptures in great earthquakes and at what rate it slips are open questions for the Pakistani Himalaya. The fact that the southern expression of the décollement, the Salt Range thrust (SRT) is localized in a thick evaporate deposit implies the fault has low strength. The lack of a strong motion event in historic records suggests no large earthquakes have struck this region in the past 2000 years. Because 101 year GPS geodetic slip rates for the SRT (~3 mm/yr) are up to four times lower than 106 year geologic rates (9-14 mm/yr), it is unknown whether the convergence rate has decreased over time, or whether the geodetic data reflect a transient phenomenon such as fault creep on the SRT. To evaluate these end members, we obtained intermediate term (104 yr) slip rates from offset geomorphic markers along the Kalabagh fault (KF). The KF is a structurally complex tear fault and lateral ramp that bounds the western side of the SRT. The bending of the western end of the SRT into the KF, and their similar geologic slip rates, suggest the faults are kinematically linked. Thus intermediate-scale slip rates and perhaps earthquake history for the KF represent a proxy for behavior of the SRT. On a section of the KF that exhibits geomorphic evidence of primarily strike slip motion, we identify two partially eroded alluvial fan apexes that are offset up to 300×25 m and 210×30 m from their source channels. Fan reconstructions suggest the offsets are probably not significantly lower than these values. Optically stimulated luminescence (OSL) ages of 23×3 ka and 16×2 ka constrain fan surface abandonment. Assuming that fan abandonment accompanied offset by the KF, both fans yield nearly identical slip rates of 13×3 mm/yr and 13×4 mm/yr for the KF. Within uncertainty, these rates are at the high end of the geologic rate for the KF and SRT, and at least several times higher than the geodetic rate for the SRT. We also identify evidence of liquefaction and fissuring in natural exposures of the KF in the walls of alluvial stream cuts. An OSL age of 6×1 ka for a sand layer that fills fault tip fissures and is cut by other fault strands indicates that the KF has experienced multiple mid-late Holocene surface ruptures. Our results favor the model where the KF and SRT are linked and that the SRT ruptures during large earthquakes, similar to behavior of the thrust front in the central Himalaya. An outstanding question not reconciled by these data is why existing GPS data are markedly lower than intermediate and long-term slip rates. One potential way to reconcile the low geodetic with the high geologic rates is to interpret the 3 mm/yr geodetic velocity as the creep rate, which implies that the ~11 mm/yr discrepancy represents the loading rate of the Main Himalaya thrust (the décollement to the north of the evaporate deposits) which is relieved in large infrequent earthquakes.

Low-temperature slip along intergrain boundaries

NASA Astrophysics Data System (ADS)

Bakai, A. S.; Lazarev, P. N.

2017-10-01

Equations are derived for slip in a disordered atomic layer which describe diffusive creep as well as high-speed slip at low temperatures. An exact solution for the slip velocity is found in the form of a functional of the distribution function of the threshold shear stresses in the slip layer. The relationship between the microscopic parameters of the theory and the macroscopic properties of metallic glass is established in terms of the Mott intergrain slip model. The calculated rate of deformation of bulk metallic glass is compared with published experimental data.

Short-and-long-term Slip Rates Along the Carboneras Fault in the Betic Cordillera, Spain

NASA Astrophysics Data System (ADS)

Khazaradze, G.; López, R.; Pallàs, R.; Ortuño, M.; Bordonau, J.; Masana, E.

2017-12-01

We present the new results from our long-standing studies to understand the geodynamic behavior of the Carboneras fault, located in the SE Betic Cordilleras of Spain. Specifically, we quantify the geodetic and geologic slip rates for the onland section of the fault. As a result of our previous GPS observations, we have been able to confirm the continuing tectonic activity of the Carboneras fault: we were able to quantify that the geodetic slip rate of the fault equals 1.3±0.2 mm/yr, expressed mainly as a left-lateral strike slip motion (Echeverria et al., 2015). In autumn 2017, with the purpose of revealing a detailed nature of the crustal deformation and its partitioning between different structures, 3 new continuous GPS stations will be established along the fault-perpendicular profile. In addition, since summer 2016, we have conducted surveys of the nearby CuaTeNeo and IGN Regente campaign points. We have also established and measured several new geodetic points in the vicinity of the fault, with the aim of increasing the spatial coverage around it. The GPS measured, short-term slip rates are in surprising agreement with the estimates of the long-term, geologic slip rates based on paleoseismic studies, which indicate a minimum strike-slip rate of 1.31 mm/yr and dip-slip rate of 0.05 mm/yr since 110.3 ka (Moreno et al. 2015). In order to increase the paleoseismic event database, several new sites have been identified along the fault, where further paleoseismic trenching surveys will be performed within the coming year or two. At the site of Tostana, located at the central part of the fault, in winter 2017 seven trenches have been opened and clear evidence of past earthquakes has been encountered. These new data, combined with the findings of the recent geomorphological study of river offsets (Ferrater, 2016) and new GPS observations, should improve the reliability of the existent deformation data and therefore, will help to better understand the seismic hazard posed by the Carbonears fault in the SE Betics. Project PREVENT (CGL2015-66263-R) financed by the Ministry of Economy, Industry and Competitiveness.

Apparent late Quaternary fault slip rate increase in the southwestern Lower Rhine Graben, central Europe

USGS Publications Warehouse

Gold, Ryan D.; Friedrich, Anke M.; Kubler, Simon; Salamon, Martin

2017-01-01

In regions of low strain, long earthquake recurrence intervals (104–106  yrs) and erosive processes limit preservation of Quaternary markers suitable for distinguishing whether faults slip at uniform or secularly varying rates. The Lower Rhine graben in the border region of Germany, The Netherlands, and Belgium provides a unique opportunity to explore Quaternary slip‐rate variations in a region of low strain using the basal (2.29±0.29  Ma) and surface (700±80  ka) contacts of the regionally extensive main terrace (“Hauptterrasse”), deposited by the Rhine and Maas Rivers. These surfaces are vertically offset 3–140 m and 0–68 m, respectively, across individual fault strands within a distributed network of northwest‐trending, slow‐slipping (<0.1  mm/yr) normal faults. In this investigation, we construct Quaternary slip histories for the southern Lower Rhine graben faults using new main terrace surface vertical offset measurements made from light detection and ranging (lidar)‐derived bare‐earth digital terrain models, which we synthesize with existing constraints on the offset basal contact of this fluvial deposit (n=91 collocated sites with displacement constraints). We find that >80% of the sites record an apparent increase in slip rate for the more recent interval from 700 ka to present, which corresponds to a period of increased uplift of the nearby Rhenish Massif and regional volcanism. However, the apparent increase in slip rate could result, in part, from erosion of the footwall surface below the main terrace, leading to an apparent displacement that is smaller than the total vertical offset since the start of the Quaternary. Prior work focused on characterization of these faults as seismic sources in the Lower Rhine graben has preferentially relied on the average fault‐slip rate constrained using the base of the main terrace. We suggest that average fault‐slip rates calculated using the ∼700  ka main terrace surface are subjected to fewer uncertainties and sample a time interval that is more relevant for seismic‐hazard analysis.

Scale dependency of fracture energy and estimates thereof via dynamic rupture solutions with strong thermal weakening

NASA Astrophysics Data System (ADS)

Viesca, R. C.; Garagash, D.

2013-12-01

Seismological estimates of fracture energy show a scaling with the total slip of an earthquake [e.g., Abercrombie and Rice, GJI 2005]. Potential sources for this scale dependency are coseismic fault strength reductions that continue with increasing slip or an increasing amount of off-fault inelastic deformation with dynamic rupture propagation [e.g., Andrews, JGR 2005; Rice, JGR 2006]. Here, we investigate the former mechanism by solving for the slip dependence of fracture energy at the crack tip of a dynamically propagating rupture in which weakening takes place by strong reductions of friction via flash heating of asperity contacts and thermal pressurization of pore fluid leading to reductions in effective normal stress. Laboratory measurements of small characteristic slip evolution distances for friction (~10 μm at low slip rates of μm-mm/s, possibly up to 1 mm for slip rates near 0.1 m/s) [e.g., Marone and Kilgore, Nature 1993; Kohli et al., JGR 2011] imply that flash weakening of friction occurs at small slips before any significant thermal pressurization and may thus have a negligible contribution to the total fracture energy [Brantut and Rice, GRL 2011; Garagash, AGU 2011]. The subsequent manner of weakening under thermal pressurization (the dominant contributor to fracture energy) spans a range of behavior from the deformation of a finite-thickness shear zone in which diffusion is negligible (i.e., undrained-adiabatic) to that in which large-scale diffusion obscures the existence of a thin shear zone and thermal pressurization effectively occurs by the heating of slip on a plane. Separating the contribution of flash heating, the dynamic rupture solutions reduce to a problem with a single parameter, which is the ratio of the undrained-adiabatic slip-weakening distance (δc) to the characteristic slip-on-a-plane slip-weakening distance (L*). However, for any value of the parameter, there are two end-member scalings of the fracture energy: for small slip, the undrained-adiabatic behavior expectedly results in fracture energy scaling as G ~ δ^2, and for large slip (where TP approaches slip on a plane) we find that G ~ δ^(2/3). This last result is a slight correction to estimates made assuming a constant, kinematically imposed slip rate and slip-on-a-plane TP resulting in G ~ δ^(1/2) [Rice, JGR 2006]. We compile fracture energy estimates of both continental and subduction zone earthquakes. In doing so, we incorporate independent estimates of fault prestress to distinguish fracture energy G from the parameter G' defined by Abercrombie and Rice [2005], which represents the energetic quantity that is most directly inferred following seismological estimates of radiated energy, seismic moment and source radius. We find that the dynamic rupture solutions (which account for the variable manner of thermal pressurization and result in a self-consistent slip rate history) allow for a close match of the estimated fracture energy over several orders of total event slip, further supporting the proposed explanation that fracture energy scaling may largely be attributed to a fault strength that weakens gradually with slip, and additionally, the potential prevalence of thermal pressurization.

Strain rate effect on fault slip and rupture evolution: Insight from meter-scale rock friction experiments

NASA Astrophysics Data System (ADS)

Xu, Shiqing; Fukuyama, Eiichi; Yamashita, Futoshi; Mizoguchi, Kazuo; Takizawa, Shigeru; Kawakata, Hironori

2018-05-01

We conduct meter-scale rock friction experiments to study strain rate effect on fault slip and rupture evolution. Two rock samples made of Indian metagabbro, with a nominal contact dimension of 1.5 m long and 0.1 m wide, are juxtaposed and loaded in a direct shear configuration to simulate the fault motion. A series of experimental tests, under constant loading rates ranging from 0.01 mm/s to 1 mm/s and under a fixed normal stress of 6.7 MPa, are performed to simulate conditions with changing strain rates. Load cells and displacement transducers are utilized to examine the macroscopic fault behavior, while high-density arrays of strain gauges close to the fault are used to investigate the local fault behavior. The observations show that the macroscopic peak strength, strength drop, and the rate of strength drop can increase with increasing loading rate. At the local scale, the observations reveal that slow loading rates favor generation of characteristic ruptures that always nucleate in the form of slow slip at about the same location. In contrast, fast loading rates can promote very abrupt rupture nucleation and along-strike scatter of hypocenter locations. At a given propagation distance, rupture speed tends to increase with increasing loading rate. We propose that a strain-rate-dependent fault fragmentation process can enhance the efficiency of fault healing during the stick period, which together with healing time controls the recovery of fault strength. In addition, a strain-rate-dependent weakening mechanism can be activated during the slip period, which together with strain energy selects the modes of fault slip and rupture propagation. The results help to understand the spectrum of fault slip and rock deformation modes in nature, and emphasize the role of heterogeneity in tuning fault behavior under different strain rates.

Surface faults on Montague Island associated with the 1964 Alaska earthquake: Chapter G in The Alaska earthquake, March 27, 1964: regional effects

USGS Publications Warehouse

Plafter, George

1967-01-01

Two reverse faults on southwestern Montague Island in Prince William Sound were reactivated during the earthquake of March 27, 1964. New fault scarps, fissures, cracks, and flexures appeared in bedrock and unconsolidated surficial deposits along or near the fault traces. Average strike of the faults is between N. 37° E. and N. 47° E.; they dip northwest at angles ranging from 50° to 85°. The dominant motion was dip slip; the blocks northwest of the reactivated faults were relatively upthrown, and both blocks were upthrown relative to sea level. No other earthquake faults have been found on land. The Patton Bay fault on land is a complex system of en echelon strands marked by a series of spectacular landslides along the scarp and (or) by a zone of fissures and flexures on the upthrown block that locally is as much as 3,000 feet wide. The fault can be traced on land for 22 miles, and it has been mapped on the sea floor to the southwest of Montague Island an additional 17 miles. The maximum measured vertical component of slip is 20 to 23 feet and the maximum indicated dip slip is about 26 feet. A left-lateral strike-slip component of less than 2 feet occurs near the southern end of the fault on land where its strike changes from northeast to north. Indirect evidence from the seismic sea waves and aftershocks associated with the earthquake, and from the distribution of submarine scarps, suggests that the faulting on and near Montague Island occurred at the northeastern end of a reactivated submarine fault system that may extend discontinuously for more than 300 miles from Montague Island to the area offshore of the southeast coast of Kodiak Island. The Hanning Bay fault is a minor rupture only 4 miles long that is marked by an exceptionally well defined almost continuous scarp. The maximum measured vertical component of slip is 16⅓ feet near the midpoint, and the indicated dip slip is about 20 feet. There is a maximum left-lateral strike-slip component of one-half foot near the southern end of the scarp. Warping and extension cracking occurred in bedrock near the midpoint on the upthrown block within about 1,000 feet of the fault scarp. The reverse faults on Montague Island and their postulated submarine extensions lie within a tectonically important narrow zone of crustal attenuation and maximum uplift associated with the earthquake. However, there are no significant lithologic differences in the rock sequences across these faults to suggest that they form major tectonic boundaries. Their spatial distribution relative to the regional uplift associated with the earthquake, the earthquake focal region, and the epicenter of the main shock suggest that they are probably subsidiary features rather than the causative faults along which the earthquake originated. Approximately 70 percent of the new breakage along the Patton Bay and the Hanning Bay faults on Montague Island was along obvious preexisting active fault traces. The estimated ages of undisturbed trees on and near the fault trace indicate that no major disc placement had occurred on these faults for at least 150 to 300 years before the 1964 earthquake.

Slip behaviour of experimental faults subjected to fluid pressure stimulation: carbonates vs. shales

NASA Astrophysics Data System (ADS)

Collettini, C.; Scuderi, M. M.; Marone, C.

2017-12-01

Fluid overpressure is one of the primary mechanisms for triggering tectonic fault slip and human-induced seismicity. This mechanism has been invoked to explain the dramatic increase in seismicity associated with waste water disposal in intra-plate setting, and it is appealing because fluids lubricate the fault and reduce the effective normal stress that holds the fault in place. Although, this basic physical mechanism is well understood, several fundamental questions remain including the apparent delay between fluid injection and seismicity, the role of fault zone rheology, and the relationship between injection volume and earthquake size. Moreover, models of earthquake nucleation predict that a reduction in normal stress, as expected for fluid overpressure, should stabilize fault slip. Here, we address these questions using laboratory experiments, conducted in the double direct shear configuration in a true-triaxial machine on carbonates and shale fault gouges. In particular, we: 1) evaluate frictional strength and permeability, 2) characterize the rate- and state- friction parameters and 3) study fault slip evolution during fluid pressure stimulations. With increasing fluid pressure, when shear and effective normal stresses reach the failure condition, in calcite gouges, characterized by slightly velocity strengthening behaviour, we observe an acceleration of slip that spontaneously evolves into dynamic failure. For shale gouges, with a strong rate-strengthening behaviour, we document complex fault slip behavior characterized by periodic accelerations and decelerations with slip velocity that remains slow (i.e. v 200 µm/s), never approaching dynamic slip rates. Our data indicate that fault rheology and fault stability is controlled by the coupling between fluid pressure and rate- and state- friction parameters suggesting that their comprehensive characterization is fundamental for assessing the role of fluid pressure in natural and human induced earthquakes.

Seismogenic Potential of a Gouge-filled Fault and the Criterion for Its Slip Stability: Constraints From a Microphysical Model

NASA Astrophysics Data System (ADS)

Chen, Jianye; Niemeijer, A. R.

2017-12-01

Physical constraints for the parameters of the rate-and-state friction (RSF) laws have been mostly lacking. We presented such constraints based on a microphysical model and demonstrated the general applicability to granular fault gouges deforming under hydrothermal conditions in a companion paper. In this paper, we examine the transition velocities for contrasting frictional behavior (i.e., strengthening to weakening and vice versa) and the slip stability of the model. The model predicts a steady state friction coefficient that increases with slip rate at very low and high slip rates and decreases in between. This allows the transition velocities to be theoretically obtained and the unstable slip regime (Vs→w < V < Vw→s) to be defined. In a spring-slider configuration, linear perturbation analysis provides analytical expressions of the critical stiffness (Kc) below which unstable slip occurs and of the critical recurrence wavelength (Wc) and static stress drop (Δμs) associated with self-sustained oscillations or stick slips. Numerical implementation of the model predicts frictional behavior that exhibits consecutive transitions from stable sliding, via periodic oscillations, to unstable stick slips with decreasing elastic stiffness or loading rate, and gives Kc, Wc, Δμs, Vs→w, and Vw→s values that are consistent with the analytical predictions. General scaling relations of these parameters given by the model are consistent with previous interpretations in the context of RSF laws and agree well with previous experiments, testifying to high validity. From these physics-based expressions that allow a more reliable extrapolation to natural conditions, we discuss the seismological implications for natural faults and present topics for future work.

Stable creeping fault segments can become destructive as a result of dynamic weakening.

PubMed

Noda, Hiroyuki; Lapusta, Nadia

2013-01-24

Faults in Earth's crust accommodate slow relative motion between tectonic plates through either similarly slow slip or fast, seismic-wave-producing rupture events perceived as earthquakes. These types of behaviour are often assumed to be separated in space and to occur on two different types of fault segment: one with stable, rate-strengthening friction and the other with rate-weakening friction that leads to stick-slip. The 2011 Tohoku-Oki earthquake with moment magnitude M(w) = 9.0 challenged such assumptions by accumulating its largest seismic slip in the area that had been assumed to be creeping. Here we propose a model in which stable, rate-strengthening behaviour at low slip rates is combined with coseismic weakening due to rapid shear heating of pore fluids, allowing unstable slip to occur in segments that can creep between events. The model parameters are based on laboratory measurements on samples from the fault of the M(w) 7.6 1999 Chi-Chi earthquake. The long-term slip behaviour of the model, which we examine using a unique numerical approach that includes all wave effects, reproduces and explains a number of both long-term and coseismic observations-some of them seemingly contradictory-about the faults at which the Tohoku-Oki and Chi-Chi earthquakes occurred, including there being more high-frequency radiation from areas of lower slip, the largest seismic slip in the Tohoku-Oki earthquake having occurred in a potentially creeping segment, the overall pattern of previous events in the area and the complexity of the Tohoku-Oki rupture. The implication that earthquake rupture may break through large portions of creeping segments, which are at present considered to be barriers, requires a re-evaluation of seismic hazard in many areas.

Triggered surface slips in the Salton Trough associated with the 1999 Hector Mine, California, earthquake

USGS Publications Warehouse

Rymer, M.J.; Boatwright, J.; Seekins, L.C.; Yule, J.D.; Liu, J.

2002-01-01

Surface fracturing occurred along the southern San Andreas, Superstition Hills, and Imperial faults in association with the 16 October 1999 (Mw 7.1) Hector Mine earthquake, making this at least the eighth time in the past 31 years that a regional earthquake has triggered slip along faults in the Salton Trough. Fractures associated with the event formed discontinuous breaks over a 39-km-long stretch of the San Andreas fault, from the Mecca Hills southeastward to Salt Creek and Durmid Hill, a distance from the epicenter of 107 to 139 km. Sense of slip was right lateral; only locally was there a minor (~1 mm) vertical component of slip. Dextral slip ranged from 1 to 13 mm. Maximum slip values in 1999 and earlier triggered slips are most common in the central Mecca Hills. Field evidence indicates a transient opening as the Hector Mine seismic waves passed the southern San Andreas fault. Comparison of nearby strong-motion records indicates several periods of relative opening with passage of the Hector Mine seismic wave-a similar process may have contributed to the field evidence of a transient opening. Slip on the Superstition Hills fault extended at least 9 km, at a distance from the Hector Mine epicenter of about 188 to 196 km. This length of slip is a minimum value, because we saw fresh surface breakage extending farther northwest than our measurement sites. Sense of slip was right lateral; locally there was a minor (~1 mm) vertical component of slip. Dextral slip ranged from 1 to 18 mm, with the largest amounts found distributed (or skewed) away from the Hector Mine earthquake source. Slip triggered on the Superstition Hills fault commonly is skewed away from the earthquake source, most notably in 1968, 1979, and 1999. Surface slip on the Imperial fault and within the Imperial Valley extended about 22 km, representing a distance from the Hector Mine epicenter of about 204 to 226 km. Sense of slip dominantly was right lateral; the right-lateral component of slip ranged from 1 to 19 mm. Locally there was a minor (~1-2 mm) vertical component of slip; larger proportions of vertical slip (up to 10 mm) occurred in Mesquite basin, where scarps indicate long-term oblique-slip motion for this part of the Imperial fault. Slip triggered on the Imperial fault appears randomly distributed relative to location along the fault and source direction. Multiple surface slips, both primary and triggered slip, indicate that slip repeatedly is small at locations of structural complexity.

Earthquake source properties from instrumented laboratory stick-slip

USGS Publications Warehouse

Kilgore, Brian D.; McGarr, Arthur F.; Beeler, Nicholas M.; Lockner, David A.; Thomas, Marion Y.; Mitchell, Thomas M.; Bhat, Harsha S.

2017-01-01

Stick-slip experiments were performed to determine the influence of the testing apparatus on source properties, develop methods to relate stick-slip to natural earthquakes and examine the hypothesis of McGarr [2012] that the product of stiffness, k, and slip duration, Δt, is scale-independent and the same order as for earthquakes. The experiments use the double-direct shear geometry, Sierra White granite at 2 MPa normal stress and a remote slip rate of 0.2 µm/sec. To determine apparatus effects, disc springs were added to the loading column to vary k. Duration, slip, slip rate, and stress drop decrease with increasing k, consistent with a spring-block slider model. However, neither for the data nor model is kΔt constant; this results from varying stiffness at fixed scale.In contrast, additional analysis of laboratory stick-slip studies from a range of standard testing apparatuses is consistent with McGarr's hypothesis. kΔt is scale-independent, similar to that of earthquakes, equivalent to the ratio of static stress drop to average slip velocity, and similar to the ratio of shear modulus to wavespeed of rock. These properties result from conducting experiments over a range of sample sizes, using rock samples with the same elastic properties as the Earth, and scale-independent design practices.

Constraining fault constitutive behavior with slip and stress heterogeneity

USGS Publications Warehouse

Aagaard, Brad T.; Heaton, T.H.

2008-01-01

We study how enforcing self-consistency in the statistical properties of the preshear and postshear stress on a fault can be used to constrain fault constitutive behavior beyond that required to produce a desired spatial and temporal evolution of slip in a single event. We explore features of rupture dynamics that (1) lead to slip heterogeneity in earthquake ruptures and (2) maintain these conditions following rupture, so that the stress field is compatible with the generation of aftershocks and facilitates heterogeneous slip in subsequent events. Our three-dimensional fmite element simulations of magnitude 7 events on a vertical, planar strike-slip fault show that the conditions that lead to slip heterogeneity remain in place after large events when the dynamic stress drop (initial shear stress) and breakdown work (fracture energy) are spatially heterogeneous. In these models the breakdown work is on the order of MJ/m2, which is comparable to the radiated energy. These conditions producing slip heterogeneity also tend to produce narrower slip pulses independent of a slip rate dependence in the fault constitutive model. An alternative mechanism for generating these confined slip pulses appears to be fault constitutive models that have a stronger rate dependence, which also makes them difficult to implement in numerical models. We hypothesize that self-consistent ruptures could also be produced by very narrow slip pulses propagating in a self-sustaining heterogeneous stress field with breakdown work comparable to fracture energy estimates of kJ/M2. Copyright 2008 by the American Geophysical Union.

Earthquake scaling laws for rupture geometry and slip heterogeneity

NASA Astrophysics Data System (ADS)

Thingbaijam, Kiran K. S.; Mai, P. Martin; Goda, Katsuichiro

2016-04-01

We analyze an extensive compilation of finite-fault rupture models to investigate earthquake scaling of source geometry and slip heterogeneity to derive new relationships for seismic and tsunami hazard assessment. Our dataset comprises 158 earthquakes with a total of 316 rupture models selected from the SRCMOD database (http://equake-rc.info/srcmod). We find that fault-length does not saturate with earthquake magnitude, while fault-width reveals inhibited growth due to the finite seismogenic thickness. For strike-slip earthquakes, fault-length grows more rapidly with increasing magnitude compared to events of other faulting types. Interestingly, our derived relationship falls between the L-model and W-model end-members. In contrast, both reverse and normal dip-slip events are more consistent with self-similar scaling of fault-length. However, fault-width scaling relationships for large strike-slip and normal dip-slip events, occurring on steeply dipping faults (δ~90° for strike-slip faults, and δ~60° for normal faults), deviate from self-similarity. Although reverse dip-slip events in general show self-similar scaling, the restricted growth of down-dip fault extent (with upper limit of ~200 km) can be seen for mega-thrust subduction events (M~9.0). Despite this fact, for a given earthquake magnitude, subduction reverse dip-slip events occupy relatively larger rupture area, compared to shallow crustal events. In addition, we characterize slip heterogeneity in terms of its probability distribution and spatial correlation structure to develop a complete stochastic random-field characterization of earthquake slip. We find that truncated exponential law best describes the probability distribution of slip, with observable scale parameters determined by the average and maximum slip. Applying Box-Cox transformation to slip distributions (to create quasi-normal distributed data) supports cube-root transformation, which also implies distinctive non-Gaussian slip distributions. To further characterize the spatial correlations of slip heterogeneity, we analyze the power spectral decay of slip applying the 2-D von Karman auto-correlation function (parameterized by the Hurst exponent, H, and correlation lengths along strike and down-slip). The Hurst exponent is scale invariant, H = 0.83 (± 0.12), while the correlation lengths scale with source dimensions (seismic moment), thus implying characteristic physical scales of earthquake ruptures. Our self-consistent scaling relationships allow constraining the generation of slip-heterogeneity scenarios for physics-based ground-motion and tsunami simulations.

Slow slip events and seismic tremor at circum-Pacific subduction zones

NASA Astrophysics Data System (ADS)

Schwartz, Susan Y.; Rokosky, Juliana M.

2007-09-01

It has been known for a long time that slip accompanying earthquakes accounts for only a fraction of plate tectonic displacements. However, only recently has a fuller spectrum of strain release processes, including normal, slow, and silent earthquakes (or slow slip events) and continuous and episodic slip, been observed and generated by numerical simulations of the earthquake cycle. Despite a profusion of observations and modeling studies the physical mechanism of slow slip events remains elusive. The concurrence of seismic tremor with slow slip episodes in Cascadia and southwestern Japan provides insight into the process of slow slip. A perceived similarity between subduction zone and volcanic tremor has led to suggestions that slow slip involves fluid migration on or near the plate interface. Alternatively, evidence is accumulating to support the notion that tremor results from shear failure during slow slip. Global observations of the location, spatial extent, magnitude, duration, slip rate, and periodicity of these aseismic slip transients indicate significant variation that may be exploited to better understand their generation. Most slow slip events occur just downdip of the seismogenic zone, consistent with rate- and state-dependent frictional modeling that requires unstable to stable transitional properties for slow slip generation. At a few convergent margins the occurrence of slow slip events within the seismogenic zone makes it highly likely that transitions in frictional properties exist there and are the loci of slow slip nucleation. Slow slip events perturb the surrounding stress field and may either increase or relieve stress on a fault, bringing it closer to or farther from earthquake failure, respectively. This paper presents a review of slow slip events and related seismic tremor observed at plate boundaries worldwide, with a focus on circum-Pacific subduction zones. Trends in global observations of slow slip events suggest that (1) slow slip is a common phenomena observed at almost all subduction zones with instrumentation capable of recording it, (2) different frictional properties likely control fast versus slow slip, (3) the depth range of slow slip may be related to the thermal properties of the plate interface, and (4) the equivalent seismic moment of slow slip events is proportional to their duration (Moατ), different from the Moατ3 scaling observed for earthquakes.

Ultra-thin clay layers facilitate seismic slip in carbonate faults.

PubMed

Smeraglia, Luca; Billi, Andrea; Carminati, Eugenio; Cavallo, Andrea; Di Toro, Giulio; Spagnuolo, Elena; Zorzi, Federico

2017-04-06

Many earthquakes propagate up to the Earth's surface producing surface ruptures. Seismic slip propagation is facilitated by along-fault low dynamic frictional resistance, which is controlled by a number of physico-chemical lubrication mechanisms. In particular, rotary shear experiments conducted at seismic slip rates (1 ms -1 ) show that phyllosilicates can facilitate co-seismic slip along faults during earthquakes. This evidence is crucial for hazard assessment along oceanic subduction zones, where pelagic clays participate in seismic slip propagation. Conversely, the reason why, in continental domains, co-seismic slip along faults can propagate up to the Earth's surface is still poorly understood. We document the occurrence of micrometer-thick phyllosilicate-bearing layers along a carbonate-hosted seismogenic extensional fault in the central Apennines, Italy. Using friction experiments, we demonstrate that, at seismic slip rates (1 ms -1 ), similar calcite gouges with pre-existing phyllosilicate-bearing (clay content ≤3 wt.%) micro-layers weaken faster than calcite gouges or mixed calcite-phyllosilicate gouges. We thus propose that, within calcite gouge, ultra-low clay content (≤3 wt.%) localized along micrometer-thick layers can facilitate seismic slip propagation during earthquakes in continental domains, possibly enhancing surface displacement.

Earthquake Clustering on Normal Faults: Insight from Rate-and-State Friction Models

NASA Astrophysics Data System (ADS)

Biemiller, J.; Lavier, L. L.; Wallace, L.

2016-12-01

Temporal variations in slip rate on normal faults have been recognized in Hawaii and the Basin and Range. The recurrence intervals of these slip transients range from 2 years on the flanks of Kilauea, Hawaii to 10 kyr timescale earthquake clustering on the Wasatch Fault in the eastern Basin and Range. In addition to these longer recurrence transients in the Basin and Range, recent GPS results there also suggest elevated deformation rate events with recurrence intervals of 2-4 years. These observations suggest that some active normal fault systems are dominated by slip behaviors that fall between the end-members of steady aseismic creep and periodic, purely elastic, seismic-cycle deformation. Recent studies propose that 200 year to 50 kyr timescale supercycles may control the magnitude, timing, and frequency of seismic-cycle earthquakes in subduction zones, where aseismic slip transients are known to play an important role in total deformation. Seismic cycle deformation of normal faults may be similarly influenced by its timing within long-period supercycles. We present numerical models (based on rate-and-state friction) of normal faults such as the Wasatch Fault showing that realistic rate-and-state parameter distributions along an extensional fault zone can give rise to earthquake clusters separated by 500 yr - 5 kyr periods of aseismic slip transients on some portions of the fault. The recurrence intervals of events within each earthquake cluster range from 200 to 400 years. Our results support the importance of stress and strain history as controls on a normal fault's present and future slip behavior and on the characteristics of its current seismic cycle. These models suggest that long- to medium-term fault slip history may influence the temporal distribution, recurrence interval, and earthquake magnitudes for a given normal fault segment.

An experimental overview of the seismic cycle

NASA Astrophysics Data System (ADS)

Spagnuolo, E.; Violay, M.; Passelegue, F. X.; Nielsen, S. B.; Di Toro, G.

2017-12-01

Earthquake nucleation is the last stage of the inter-seismic cycle where the fault surface evolves through the interplay of friction, healing, stress perturbations and strain events. Slip stability under rate-and state friction has been extensively discussed in terms of loading point velocity and equivalent fault stiffness, but fault evolution towards seismic runaway under complex loading histories (e.g. slow variations of tectonic stress, stress transfer from impulsive nearby seismic events) is not yet fully investigated. Nevertheless, the short term earthquake forecasting is based precisely on a relation between seismic productivity and loading history which remains up to date still largely unresolved. To this end we propose a novel experimental approach which avails of a closed loop control of the shear stress, a nominally infinite equivalent slip and transducers for continuous monitoring of acoustic emissions. This experimental simulation allows us to study the stress dependency and temporal evolution of spontaneous slip events occurring on a pre-existing fault subjected to different loading histories. The experimental fault has an initial roughness which mimic a population of randomly distributed asperities, which here are used as a proxy for patches which are either far or close to failure on an extended fault. Our observations suggest that the increase of shear stress may trigger either spontaneous slow slip (creep) or short-lived stick-slip bursts, eventually leading to a fast slip instability (seismic runaway) when slip rates are larger than a few cm/s. The event type and the slip rate are regulated at first order by the background shear stress whereas the ultimate strength of the entire fault is dominated by the number of asperities close to failure under a stress step. The extrapolation of these results to natural conditions might explain the plethora of events that often characterize seismic sequences. Nonetheless this experimental approach helps the definition of a scaling relation between the loading rate and cumulated slip which is relevant to the definition of a recurrence model for the seismic cycle.

Late Holocene slip rate and ages of prehistoric earthquakes along the Maacama Fault near Willits, Mendocino County, northern California

USGS Publications Warehouse

Prentice, Carol S.; Larsen, Martin C.; Kelsey, Harvey M.; Zachariasen, Judith

2014-01-01

The Maacama fault is the northward continuation of the Hayward–Rodgers Creek fault system and creeps at a rate of 5.7±0.1  mm/yr (averaged over the last 20 years) in Willits, California. Our paleoseismic studies at Haehl Creek suggest that the Maacama fault has produced infrequent large earthquakes in addition to creep. Fault terminations observed in several excavations provide evidence that a prehistoric surface‐rupturing earthquake occurred between 1060 and 1180 calibrated years (cal) B.P. at the Haehl Creek site. A folding event, which we attribute to a more recent large earthquake, occurred between 790 and 1060 cal B.P. In the last 560–690 years, a buried channel deposit has been offset 4.6±0.2  m, giving an average slip rate of 6.4–8.6  mm/yr, which is higher than the creep rate over the last 20 years. The difference between this slip rate and the creep rate suggests that coseismic slip up to 1.7 m could have occurred after the formation of the channel deposit and could be due to a paleoearthquake known from paleoseismic studies in the Ukiah Valley, about 25 km to the southeast. Therefore, we infer that at least two, and possibly three, large earthquakes have occurred at the Haehl Creek site since 1180 cal B.P. (770 C.E.), consistent with earlier studies suggesting infrequent, large earthquakes on the Maacama fault. The short‐term geodetic slip rate across the Maacama fault zone is approximately twice the slip rate that we have documented at the Haehl Creek site, which is averaged over the last approximately 600 years. If the geodetic rate represents the long‐term slip accumulation across the fault zone, then we infer that, in the last ∼1200 years, additional earthquakes may have occurred either on the Haehl Creek segment of the Maacama fault or on other active faults within the Maacama fault zone at this latitude.

Geodesy- and geology-based slip-rate models for the Western United States (excluding California) national seismic hazard maps

USGS Publications Warehouse

Petersen, Mark D.; Zeng, Yuehua; Haller, Kathleen M.; McCaffrey, Robert; Hammond, William C.; Bird, Peter; Moschetti, Morgan; Shen, Zhengkang; Bormann, Jayne; Thatcher, Wayne

2014-01-01

The 2014 National Seismic Hazard Maps for the conterminous United States incorporate additional uncertainty in fault slip-rate parameter that controls the earthquake-activity rates than was applied in previous versions of the hazard maps. This additional uncertainty is accounted for by new geodesy- and geology-based slip-rate models for the Western United States. Models that were considered include an updated geologic model based on expert opinion and four combined inversion models informed by both geologic and geodetic input. The two block models considered indicate significantly higher slip rates than the expert opinion and the two fault-based combined inversion models. For the hazard maps, we apply 20 percent weight with equal weighting for the two fault-based models. Off-fault geodetic-based models were not considered in this version of the maps. Resulting changes to the hazard maps are generally less than 0.05 g (acceleration of gravity). Future research will improve the maps and interpret differences between the new models.

Rates and patterns of surface deformation from laser scanning following the South Napa earthquake, California

USGS Publications Warehouse

DeLong, Stephen B.; Lienkaemper, James J.; Pickering, Alexandra J; Avdievitch, Nikita N.

2015-01-01

The A.D. 2014 M6.0 South Napa earthquake, despite its moderate magnitude, caused significant damage to the Napa Valley in northern California (USA). Surface rupture occurred along several mapped and unmapped faults. Field observations following the earthquake indicated that the magnitude of postseismic surface slip was likely to approach or exceed the maximum coseismic surface slip and as such presented ongoing hazard to infrastructure. Using a laser scanner, we monitored postseismic deformation in three dimensions through time along 0.5 km of the main surface rupture. A key component of this study is the demonstration of proper alignment of repeat surveys using point cloud–based methods that minimize error imposed by both local survey errors and global navigation satellite system georeferencing errors. Using solid modeling of natural and cultural features, we quantify dextral postseismic displacement at several hundred points near the main fault trace. We also quantify total dextral displacement of initially straight cultural features. Total dextral displacement from both coseismic displacement and the first 2.5 d of postseismic displacement ranges from 0.22 to 0.29 m. This range increased to 0.33–0.42 m at 59 d post-earthquake. Furthermore, we estimate up to 0.15 m of vertical deformation during the first 2.5 d post-earthquake, which then increased by ∼0.02 m at 59 d post-earthquake. This vertical deformation is not expressed as a distinct step or scarp at the fault trace but rather as a broad up-to-the-west zone of increasing elevation change spanning the fault trace over several tens of meters, challenging common notions about fault scarp development in strike-slip systems. Integrating these analyses provides three-dimensional mapping of surface deformation and identifies spatial variability in slip along the main fault trace that we attribute to distributed slip via subtle block rotation. These results indicate the benefits of laser scanner surveys along active faults and demonstrate that fine-scale variability in fault slip has been missed by traditional earthquake response methods.

The influence of slip velocity and temperature on permeability during and after high-velocity fault slip

NASA Astrophysics Data System (ADS)

Tanikawa, W.; Mukoyoshi, H.; Tadai, O.; Hirose, T.; Lin, W.

2011-12-01

Fluid transport properties in fault zones play an important role in dynamic processes during large earthquakes. If the permeability in a fault zone is low, high pore-fluid pressures caused by thermal pressurization (Sibson, 1973) or shear-induced compaction (Blanpied et al., 1992) can lead to an apparent reduction of fault strength. Changes in porosity and permeability of fault rocks within a fault zone during earthquakes and the subsequent progressive recovery of these properties may have a large influence on earthquake recurrence (Sleep and Blanpied, 1992). A rotary shear apparatus was used to investigate changes of fluid transport properties in a fault zone by real-time measurement of gas flow rates during and after shearing of hollow sandstone and granite cylinders at various slip rates. Our apparatus measures permeability parallel to the slip plane in both the slip zone and wall rocks. In all cases, permeability decreased rapidly with an increase of friction, but recovered soon after slip, reaching a steady state within several tens of minutes. The rate of reduction of permeability increased with increasing slip velocity. Permeability did not recover to pre-slip levels after low-velocity tests but recovered to exceed them after high-velocity tests. Frictional heating of gases at the slip surface increased gas viscosity, which increased gas flow rate to produce an apparent permeability increase. The irreversible permeability changes of the low-velocity tests were caused by gouge formation due to wearing and smoothing of the slip surface. The increase of permeability after high-velocity tests was caused by mesoscale fracturing in response to rapid temperature rise. Changes of pore fluid viscosity contributed more to changes of flow rate than did permeability changes caused by shear deformation, although test results from different rocks and pore fluids might be different. References Blanpied, M.L., Lockner, D.A., Byerlee, J.D., 1992. An earthquake mechanism based on rapid sealing of faults. Nature 358, 574-576 Sibson, R.H., 1973. Interactions between temperature and pore fluid pressure during earthquake faulting: A mechanism for partial or total stress relief. Nature 243, 66-68. Sleep, N.H., Blanpied, M.L., 1992. Creep, compaction and the weak rheology of major faults. Nature 359, 687-692.

Incremental slip rate and paleoseismic data from the eastern Hope fault, New Zealand: the Hossack and Green Burn sites

NASA Astrophysics Data System (ADS)

Hatem, A. E.; Dolan, J. F.; Langridge, R.; Zinke, R. W.; McGuire, C. P.; Rhodes, E.; Van Dissen, R. J.

2016-12-01

We present incremental slip rate and paleo-earthquake data from the Conway segment of the eastern Hope fault, within the Marlborough Fault System (MFS) in the northern South Island of New Zealand. Our incremental slip rate site at Hossack Station is located near the western boundary of the Conway segment (near the Hanmer pull-apart basin), and preserves four offsets of the Hossack Stream channel that range in size from c. 11 to 190 m. Channel cut and fill deposits were exposed in several fault-parallel (channel perpendicular) trenches, and the initiation and abandonment of these offset channels are constrained by >60 radiocarbon ages, yielding four incremental slip rates spanning the Holocene. Our paleoseismologic trench at Green Burn, at the eastern end of the Conway segment near Kaikoura, was excavated across the 5-m-high fault scarp into the adjacent bog deposits. This fault-perpendicular trench revealed evidence for at least four paleo-earthquakes with age constraints provided by >40 radiocarbon dates. These results add to a growing body of slip rate and paleo-earthquake age and displacement data from all four main strike-slip faults that comprise the MFS. Collectively, these observations from the Hope fault are beginning to reveal the detailed system-level behavior of the four main faults in the MFS, with fundamental implications for, among other things, earthquake occurrence and behavior, as well as seismic hazard assessment.

Friction falls towards zero in quartz rock as slip velocity approaches seismic rates.

PubMed

Di Toro, Giulio; Goldsby, David L; Tullis, Terry E

2004-01-29

An important unsolved problem in earthquake mechanics is to determine the resistance to slip on faults in the Earth's crust during earthquakes. Knowledge of coseismic slip resistance is critical for understanding the magnitude of shear-stress reduction and hence the near-fault acceleration that can occur during earthquakes, which affects the amount of damage that earthquakes are capable of causing. In particular, a long-unresolved problem is the apparently low strength of major faults, which may be caused by low coseismic frictional resistance. The frictional properties of rocks at slip velocities up to 3 mm s(-1) and for slip displacements characteristic of large earthquakes have been recently simulated under laboratory conditions. Here we report data on quartz rocks that indicate an extraordinary progressive decrease in frictional resistance with increasing slip velocity above 1 mm s(-1). This reduction extrapolates to zero friction at seismic slip rates of approximately 1 m s(-1), and appears to be due to the formation of a thin layer of silica gel on the fault surface: it may explain the low strength of major faults during earthquakes.

Surface slip during large Owens Valley earthquakes

USGS Publications Warehouse

Haddon, E.K.; Amos, C.B.; Zielke, O.; Jayko, Angela S.; Burgmann, R.

2016-01-01

The 1872 Owens Valley earthquake is the third largest known historical earthquake in California. Relatively sparse field data and a complex rupture trace, however, inhibited attempts to fully resolve the slip distribution and reconcile the total moment release. We present a new, comprehensive record of surface slip based on lidar and field investigation, documenting 162 new measurements of laterally and vertically displaced landforms for 1872 and prehistoric Owens Valley earthquakes. Our lidar analysis uses a newly developed analytical tool to measure fault slip based on cross-correlation of sublinear topographic features and to produce a uniquely shaped probability density function (PDF) for each measurement. Stacking PDFs along strike to form cumulative offset probability distribution plots (COPDs) highlights common values corresponding to single and multiple-event displacements. Lateral offsets for 1872 vary systematically from ∼1.0 to 6.0 m and average 3.3 ± 1.1 m (2σ). Vertical offsets are predominantly east-down between ∼0.1 and 2.4 m, with a mean of 0.8 ± 0.5 m. The average lateral-to-vertical ratio compiled at specific sites is ∼6:1. Summing displacements across subparallel, overlapping rupture traces implies a maximum of 7–11 m and net average of 4.4 ± 1.5 m, corresponding to a geologic Mw ∼7.5 for the 1872 event. We attribute progressively higher-offset lateral COPD peaks at 7.1 ± 2.0 m, 12.8 ± 1.5 m, and 16.6 ± 1.4 m to three earlier large surface ruptures. Evaluating cumulative displacements in context with previously dated landforms in Owens Valley suggests relatively modest rates of fault slip, averaging between ∼0.6 and 1.6 mm/yr (1σ) over the late Quaternary.

Crustal Strike-Slip Faulting along Small Circle Paths in the Northwestern United States

NASA Astrophysics Data System (ADS)

Brocher, T. M.; Wells, R. E.; Lamb, A. P.; Weaver, C. S.

2015-12-01

Late Cenozoic and Quaternary faults, seismicity lineaments, and focal mechanisms provide evidence that clockwise rotation of Washington and Oregon is accommodated by north-directed thrusting and strike-slip deformation in the Washington segment of the Cascadia forearc. Curvilinear NW- to NNW-trending high-angle strike-slip faults and seismicity lineaments define small circles around an Euler pole (117.7°W, 47.9°N) of rotation relative to North America that approximates GPS-derived poles for the rotation of eastern Washington and the Snake River Plain. Although the lengths of strike-slip faults that follow small circle paths suggest maximum earthquake magnitudes of M6.6 to M7.2, their slip rates calculated from the Euler pole are low (0.3 to 0.5 mm/yr). Many normal faults in the Lewis and Clark Zone in Montana, the Centennial fault system north of the Snake River Plain, west of the Wasatch Front, in the northern Basin and Range, and locally east of the Oregon Cascade arc are radial to this pole of rotation, suggesting that these normal faults help accommodate this crustal rotation. Regions undergoing contraction in western Washington and northwestern Oregon are separated from those to the east undergoing extension by lines radial to the Euler pole. In our regional kinematic model, dextral faults along small circles connect SW-directed crustal extension in the Intermountain Seismic Belt and E-directed extension in the Cascade arc south of Mount Hood to N-directed contraction in the Olympic Peninsula, Puget Lowland, and the Yakima Fold and Thrust Belt. The lack of Quaternary faulting and seismicity in the Oregon segment of the forearc is consistent with its clockwise rotation as a rigid block. Potential drivers of the crustal rotation include westward slab rollback and the Yellowstone geoid high, and the overall velocity field may integrate the response of rotating blocks and distributed deformation between them.

Holocene slip rates along the San Andreas Fault System in the San Gorgonio Pass and implications for large earthquakes in southern California

NASA Astrophysics Data System (ADS)

Heermance, Richard V.; Yule, Doug

2017-06-01

The San Gorgonio Pass (SGP) in southern California contains a 40 km long region of structural complexity where the San Andreas Fault (SAF) bifurcates into a series of oblique-slip faults with unknown slip history. We combine new 10Be exposure ages (Qt4: 8600 (+2100, -2200) and Qt3: 5700 (+1400, -1900) years B.P.) and a radiocarbon age (1260 ± 60 years B.P.) from late Holocene terraces with scarp displacement of these surfaces to document a Holocene slip rate of 5.7 (+2.7, -1.5) mm/yr combined across two faults. Our preferred slip rate is 37-49% of the average slip rates along the SAF outside the SGP (i.e., Coachella Valley and San Bernardino sections) and implies that strain is transferred off the SAF in this area. Earthquakes here most likely occur in very large, throughgoing SAF events at a lower recurrence than elsewhere on the SAF, so that only approximately one third of SAF ruptures penetrate or originate in the pass.