Increase In Slip Rate Research Articles

A decadal‐scale deformation transient prior to the 2011 Mw 9.0 Tohoku‐oki earthquake

AbstractGPS time series in northeast Japan exhibit nonlinear trends from 1996 to 2011 before the Mw 9.0, 2011 Tohoku‐oki earthquake. After removing reference frame noise, we model time series as linear trends plus constant acceleration, correcting for coseismic and postseismic effects from the numerous Mw ∼ 6.5+ earthquakes during this period. We find spatially coherent and statistically significant accelerations throughout northern Honshu. Large areas of Japan outside the Tohoku region show insignificant accelerations, demonstrating that the observation is not due to network‐wide artifacts. While the accelerations in northern Tohoku (Sanriku area) can be explained by decaying postseismic deformation from pre‐1996 earthquakes, the accelerations in south‐central Tohoku appear unrelated to postseismic effects. The latter accelerations are associated with a decrease in average trench‐normal strain rate and can be explained by increasing slip rate on the Japan trench plate interface and/or updip migration of deep aseismic slip in the decades before the 2011 Tohoku‐oki earthquake.

Spatial and temporal variation of palaeoseismic activity at an intraplate, historically quiescent structure: The Concud fault (Iberian Chain, Spain)

Several faults in the Teruel and Jiloca grabens (Iberian Chain, NE Spain), particularly the targeted Concud fault, show evidences of recent, continuous activity, despite their scarce instrumental and historic seismic record.Three trenches are studied in two locations (central and southeastern sectors of the Concud fault, respectively). After comparing with previous works, we reconstruct a palaeoseismic succession with nine events distributed along a maximum time lapse bracketed between 81.6 and 14.0ka. This succession involves an average recurrence interval of 7.4±2.8ka, with individual interseismic periods between 4 and 11ka. The calculated coseismic displacements range from 0.6 to 2.7m, with an average value of 1.9m that results in a slip rate of 0.26mm/a. Due to the incomplete sedimentary record for Holocene times, we cannot affirm that the youngest event detected was actually the last one. We conjecture that some other events may have occurred during the period between 15.0 and 3.4ka.Temporal and spatial variations have been detected in palaeoseismic activity, specifically in the distribution of coseismic displacements. First, a non-steady slip rate is evidenced during Plio-Pleistocene times: a long-term tendency towards increasing slip rate is modulated in detail by the occurrence of minor cycles, as the sequence of increasing/decreasing activity recorded within the studied time window suggests. Secondly, an asymmetric distribution of coseismic slip along the fault trace is observed, paralleling the distribution of total fault throw, which shows an absolute maximum close to the southeastern tip. A combination of factors is proposed to explain this: branching of the main fault; dominant, remote-stress-driven slip towards N 220° E on the NW–SE fault segment; guided movement on the passive, NNW–SSE segment giving rise to an oblique roll-over monocline; and decoupling of the hanging-wall block owing to the transverse Los Mansuetos–Valdecebro fault zone.

A two‐scale model for sheared fault gouge: Competition between macroscopic disorder and local viscoplasticity

AbstractWe develop a model for sheared gouge layers that accounts for the local increase in temperature at the grain contacts during sliding. We use the shear transformation zone theory, a statistical thermodynamic theory, to describe irreversible macroscopic plastic deformations due to local rearrangements of the gouge particles. We track the temperature evolution at the grain contacts using a one‐dimensional heat diffusion equation. At low temperatures, the strength of the asperities is limited by the flow strength, as predicted by dislocation creep models. At high temperatures, some of the constituents of the grains may melt leading to the degradation of the asperity strength. Our model predicts a logarithmic rate dependence of the steady state shear stress in the quasistatic regime. In the dense flow regime the frictional strength decreases rapidly with increasing slip rate due to thermal softening at the granular interfaces. The transient response following a step in strain rate includes a direct effect and a following evolution effect, both of which depend on the magnitude and direction of the velocity step. In addition to frictional heat, the energy budget includes an additional energy sink representing the fraction of external work consumed in increasing local disorder. The model links low‐speed and high‐speed frictional response of gouge layers and provides an essential ingredient for multiscale modeling of earthquake ruptures with enhanced coseismic weakening.

Fault network modeling of crustal deformation in California constrained using GPS and geologic observations

Abstract We have developed a kinematic fault network model of crustal deformation in an elastic half-space. Surface deformation is calculated using this model assuming each fault segment slipping beneath a locking depth. Each fault segment connects to its adjacent elements with slip vector continuity imposed at fault nodes or intersections; the degree of the constraints determines whether deformation is block-like or not. We apply this model to invert GPS observations for slip rates on major faults in California with geological rate constraints. Based on the F-test result, we find that lesser block-like models fit the data significantly better than the strictly block-like model. Our final inversion shows a slip rate varying from 20 to 23 mm/yr along the northern San Andreas from the Santa Cruz to the North Coast segment. Slip rates vary from 9 to 13 mm/yr along the Hayward to the Maacama fault segment, and from 15 to 3 mm/yr along the central Calaveras to the West Napa fault segment. For the central California Creeping Zone, the result suggests a depth dependent creep rate with an average of 22 mm/yr over the top 5 km and 32 mm/yr underneath. From the Mojave to San Bernardino Mountain segments, we also find a significant decrease in slip rate along the San Andreas in comparison with the geologic rates, in contrast to a significant increase in slip rate on faults along the eastern California shear zone. Along the southern San Andreas, slip rates vary from 21 to 25 mm/yr from the Coachella Valley to Imperial Valley segments. Slip rates range from 0 to 3 mm/yr across the western Transverse Ranges faults, which is consistent with the regional crustal thickening. Overall slip rates derived from geodetic observations correlate strongly with the geologic slip rates statistically, suggesting high compatibility between geodetic and geologic observations.

Are the frictional properties of creeping faults persistent? Evidence from rapid afterslip following the 2011 Tohoku‐oki earthquake

Geophysical observations and numerical studies have shown that creeping portions of faults have persistent rate‐strengthening frictional properties and can act as barriers to earthquake rupture propagation. On the basis of GPS data following the 2011 MW 9.0 Tohoku‐oki earthquake in Japan, we find that the evolution of afterslip and postseismic shear stress on the plate interface is inconsistent with persistent rate‐strengthening frictional properties but is consistent with slip‐rate‐dependent frictional properties that exhibit less rate‐strengthening with increasing slip rate. Such slip‐rate‐dependent frictional properties tend to prevent creeping regions from acting as barriers to rupture propagation and therefore could be an important factor in determining the spatial extent of individual earthquakes.

Active forearc shortening in Tohoku, Japan: Constraints on fault geometry from erosion rates and fluvial longitudinal profiles

Convexities in the longitudinal profiles of actively incising rivers are typically considered to represent the morphologic signal of a transient response to external perturbations in tectonic or climatic forcing. Distinguishing such knickzones from those that may be anchored to the channel network by spatial variations in rock uplift, however, can be challenging. Here, we combine stream profile analysis, 10Be watershed-averaged erosion rates, and numerical modeling of stream profile evolution to evaluate whether knickzones in the Abukuma massif of northeast Japan represent a temporal or spatial change in rock uplift rate in relation to forearc shortening. Knickzones in channels that drain the eastern flank of the Abukuma massif are characterized by breaks in slope–area scaling and separate low-gradient, alluvial upper-channel segments from high-gradient, deeply-incised lower channel segments. Average erosion rates inferred from 10Be concentrations in modern sediment below knickzones exceed erosion rates above knickzones by 20–50%. Although profile convexities could be interpreted as a transient response to an increase in rock uplift rate associated with slip on the range-bounding fault, geologic constraints on the initiation of fault slip and the magnitude of displacement cannot be reconciled with a recent, spatially uniform increase in slip rate. Rather, we find that knickzone position, stream profile gradients, and basin averaged erosion rates are best explained by a relatively abrupt spatial increase in uplift rate localized above a flat-ramp transition in the fault system. These analyses highlight the importance of considering spatially non-uniform uplift in the interpretation of stream profile evolution and demonstrate that the adjustment of river profiles to fault displacement can provide constraints on fault geometry in actively eroding landscapes.

The Qs problem: Sediment volumetric balance of proximal foreland basin systems

AbstractAlthough the stratigraphy of sedimentary basins depends on the balance between the magnitude and grain‐size characteristics of the sediment supply (Qs) and the spatial distribution of tectonic subsidence generating accommodation σ(x), Qs is problematical to measure in present‐day sediment routing systems and formidably difficult to predict in their ancient counterparts. This challenge was tackled by treating the sediment discharge from the outlet of mountain catchments as the result of incision by a drainage network with a bulk diffusivity based on the length over which the mean annual rainfall is concentrated. The size, relief and slope of palaeo‐catchments acting as feeders for sediment routing systems are used to run simulations of sediment discharge and bulk diffusivity for a range of annual precipitation values. A wide range of observable geological phenomena can be used to converge on the most likely solutions for Qs, including depositional volumes in the basin, and bedrock thermochronology and detrital cosmogenic nuclide dating to constrain catchment erosion rates. Modelled sediment discharges can be checked with estimates derived from global regressions. The sediment efflux of mountain catchments serves as a boundary condition for down‐system sediment transport and deposition. Variations in the volumetric ratio of sediment supply to available accommodation, Qs/σ(x), determines patterns of transverse versus longitudinal (axial) sediment dispersal. The volumetric ratio may change as a result of variations in climatic parameters, tectonic uplift rate and catchment expansion. An abrupt climate change to higher precipitation values promotes higher Qs/σ(x), but transient landscape response causes a return to values close to the baseline, generating a distinctive down‐system extension of a gravel ‘spike’. Catchment expansion has a similar, but more prolonged, effect on gravel progradation. In contrast, a change in tectonic forcing, such as an increase in slip rate on a border fault, causes little change in Qs/σ(x), because increased subsidence compensates for the increased sediment supply. Studies of mid Eocene–Oligocene sediment routing systems in the south‐central Pyrenees allow the discrimination of different types of proximal wedge‐top sedimentary systems on the basis of the volumetric ratio of Qs to accommodation σ(x): (i) small, steep, local fan systems in tectonically ponded, underfilled basins, supplied by low sediment discharges; (ii) tectonically guided, long‐range, axial systems fed by large sediment discharges from widely spaced palaeovalleys; and (iii) large, shallow‐sloping transverse megafans burying underlying defunct or active tectonic structures, supplied by high to very high sediment discharges. Understanding the role of variations in Qs helps to explain the syntectonic evolution of proximal foreland basin systems. The Oligocene–Miocene North Alpine Foreland Basin, Switzerland, is qualitatively identified as a high‐Qs example, the Miocene–Recent northern Apennines of Italy as a low‐Qs example and the Eocene‐Oligocene southern Pyrenees of Spain as intermediate in character.

Multi-timescale mechanical coupling between the San Jacinto fault and the San Andreas fault, southern California

Fault interaction is believed to influence seismicity and crustal deformation, but the mechanics of fault interaction over various time scales remain poorly understood. We present here a numerical investigation of fault coupling and interaction over multiple time scales, using the San Andreas fault and the San Jacinto fault in southern California as an example. The San Andreas fault is the Pacific–North American plate boundary, but in southern California, a significant portion of the relative plate motion is accommodated by the subparallel San Jacinto fault. We developed a three-dimensional viscoelastoplastic finite-element model to study the ways in which these two faults may have interacted (1) during and following individual earthquakes, (2) over multiple seismic cycles, and (3) during long-term steady-state fault slip. Our results show that the cluster of nine moderate-sized earthquakes (M 6–7) on the San Jacinto fault since 1899 may have lowered the Coulomb stress on the southern San Andreas fault, delaying the “Big One,” an earthquake of magnitude 7.8 or greater that may result from rupture of much of the southern San Andreas fault. In addition to the static Coulomb stress changes associated with individual earthquakes, variations of seismicity over seismic cycles on one fault can influence the loading rate on the other fault. When the San Jacinto fault experiences clusters of earthquakes such as those in the past century, the loading rate on the San Andreas fault can be lowered by as much as ∼80%. Over longer time scales, these two faults share the slip needed to accommodate the relative plate motion. Hence, an increase in slip rate on one of these two faults causes complementary decrease on the other, which is consistent with geological observations.

Reduction in BET surface area of Nojima fault gouge with seismic slip and its implication for the fracture energy of earthquakes

A common view concerning the energetics of seismogenic fault motion is that at least part of the fracture energy is consumed in grain crushing in the fault zone, and that this part may be estimated by grain-size analysis of fault rocks. We address this problem by conducting room-dry friction experiments on Nojima fault gouge at subseismic to seismic slip rates (0.009–1.31m/s) and at normal stresses up to 3.64MPa, and by measuring the BET surface area of the gouge before and after the experiments. Where it cuts granite, the Nojima fault zone has BET surface area of about 65×106m2 per unit fault area (1m2). Clayey and granular fault gouges, composed mainly of quartz, plagioclase, kaolinite and smectite, were collected from a granitic fault zone at a new outcrop in Funaki, Awaji Island, southwest Japan. Both clayey and granular gouges exhibit dramatic weakening at high slip rates. Specific BET surface areas of clayey and granular gouges decreased with increasing slip rate from 46.0 and 15.4m2/g before deformation to about 20 and 5m2/g after deformation (55–70% reduction), respectively. Microstructural observations revealed that grain welding within the slip zones at high slip rates reduced grain surface area. The energetics of seismic fault motion should be examined with broader views taking into account grain crushing, grain welding, decomposition and frictional melting.

Frictional melting of gabbro under extreme experimental conditions of normal stress, acceleration, and sliding velocity

[1] With the advent of high-velocity shear apparatus, several experimental studies have been performed in recent years, improving our understanding of the evolution of fault strength during seismic slip. However, these experiments were conducted under relatively low normal stress (<20 MPa) and using small cylindrical samples where a large gradient in slip velocity exists across the sliding surface. Given the above limitations, the extrapolation of these experimental results to natural conditions is not trivial. Here we present results from an experimental study on gabbroic rocks using a newly developed rotary shear apparatus capable of reaching higher normal stress (up to 50 MPa) on ring-shaped samples (30/50 mm internal/external diameter) and allowing precise control of the imposed slip velocity function. The results confirm that steady state shear stress during the melt-lubricated phase of the experiment depends on normal stress in the form of a power law equation as predicted by theoretical models. However, the exponent appears closer to 0.5, contrary to the theoretical prediction of 0.25. We observe no systematic dependence of shear stress on acceleration, but increasing deceleration drastically decreases the recovery of friction during final slip. We find that the slip-weakening distance decreases inversely with increasing normal stress, in agreement with theoretical considerations, and decreases with increasing slip rate. Extrapolation of the slip-weakening distance to natural conditions predicts a slip velocity for ancient seismic events of 0.3–1 m/s when compared with field estimates. These values compare well with seismological estimates.

Granular nanoparticles lubricate faults during seismic slip

Research Article| June 01, 2011 Granular nanoparticles lubricate faults during seismic slip Raehee Han; Raehee Han * 1Geologic Environment Division, Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon 305-350, South Korea *E-mail: raeheehan@kigam.re.kr. Search for other works by this author on: GSW Google Scholar Takehiro Hirose; Takehiro Hirose 2Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Kochi 783-8502, Japan Search for other works by this author on: GSW Google Scholar Toshihiko Shimamoto; Toshihiko Shimamoto 3State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, P.O. Box 9803, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Youngmin Lee; Youngmin Lee 4Geological Research Division, Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon 305-350, South Korea Search for other works by this author on: GSW Google Scholar Jun-ichi Ando Jun-ichi Ando 5Department of Earth and Planetary Systems Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan Search for other works by this author on: GSW Google Scholar Geology (2011) 39 (6): 599–602. https://doi.org/10.1130/G31842.1 Article history received: 21 Oct 2010 rev-recd: 14 Feb 2011 accepted: 15 Feb 2011 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Raehee Han, Takehiro Hirose, Toshihiko Shimamoto, Youngmin Lee, Jun-ichi Ando; Granular nanoparticles lubricate faults during seismic slip. Geology 2011;; 39 (6): 599–602. doi: https://doi.org/10.1130/G31842.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Nanoparticles are known to form in narrow slip zones in natural and experimental fault zones, but their possible role in dynamic weakening of faults during seismic slip remains almost unexplored. We conducted friction experiments on periclase (MgO) nanoparticles (50 nm in average size) at rates as high as 1.3 m s−1, a typical speed of seismic slip. The nanoparticles were used as the initial gouge to avoid complexities arising from comminution and fluid release. The dynamic friction decreased with increasing slip rate and the steady-state frictional coefficient reduced to as low as 0.1 at a slip rate of 1.3 m s−1. Flash heating is not effective for nanoparticles, and we propose that development of slickensides and dominant operation of nanoparticle rolling cause such a weakening. Nanoparticle lubrication appears to be as effective as melt lubrication and thermal pressurization, and the formation of nanoparticles in slip zones may be an important fault lubrication process. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Acceleration and evolution of faults: An example from the Hunter Mountain–Panamint Valley fault zone, Eastern California

We present new space geodetic data indicating that the present slip rate on the Hunter Mountain–Panamint Valley fault zone in Eastern California (5.0±0.5mm/yr) is significantly faster than geologic estimates based on fault total offset and inception time. We interpret this discrepancy as evidence for an accelerating fault and propose a new model for fault initiation and evolution. In this model, fault slip rate initially increases with time; hence geologic estimates averaged over the early stages of the fault's activity will tend to underestimate the present-day rate. The model is based on geologic data (total offset and fault initiation time) and geodetic data (present day slip rate). The model assumes a monotonic increase in slip rate with time as the fault matures and straightens. The rate increase follows a simple Rayleigh cumulative distribution. Integrating the rate-time path from fault inception to present-day gives the total fault offset.

Late Quaternary crustal shortening rate across the Shinjo basin, northeast Japan

The active fault and fold belt in the eastern Shinjo basin has contributed to late Quaternary crustal shortening of the northeastern Japan arc. The geometries of several deformed strata and geomorphic surfaces recorded different rates of cumulative shortening. Fluvial terraces as old as 290 ka were dated by 14C and fission track dating and tephrochronology. We used published seismic profiles to constrain the deep structure of the belt. Vertical offsets of different terrace surfaces show that the slip rate of the Chojahara fault in the innermost basin has increased through time. On the basis of its seismic profile, this fault was interpreted to dip at a high angle. The Funagata anticline between the Chojahara fault and the Ou ranges was probably caused by a low‐angle blind thrust at about a 2 km depth. The different geometries between the basin sediments and fluvial terraces caused by the blind thrust indicate downward propagation of the thrust through time. Synchronous development of the Chojahara fault (increased slip rate) and the blind thrust beneath the Funagata anticline (downward propagation) suggests that these faults form a piggyback fault system connecting to the deep part of the basin‐bounding Kyodanbara fault. Estimated crustal shortening rates are averaged to be 0.65–1.05 and 0.79–1.42 m/kyr over the last 200–260 and 12–28 ka, respectively, accounting for about 0.7–1.6% of the convergence between the Pacific and Eurasian plates. Estimated strain rates are 0.07–0.11 and 0.08–0.14 ppm/yr for the last 200–260 and 12–28 ka, respectively.

Evolving geometrical heterogeneities of fault trace data

SUMMARY 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.

Response of faults to climate-driven changes in ice and water volumes on Earth’s surface

Numerical models including one or more faults in a rheologically stratified lithosphere show that climate-induced variations in ice and water volumes on Earth's surface considerably affect the slip evolution of both thrust and normal faults. In general, the slip rate and hence the seismicity of a fault decreases during loading and increases during unloading. Here, we present several case studies to show that a postglacial slip rate increase occurred on faults worldwide in regions where ice caps and lakes decayed at the end of the last glaciation. Of note is that the postglacial amplification of seismicity was not restricted to the areas beneath the large Laurentide and Fennoscandian ice sheets but also occurred in regions affected by smaller ice caps or lakes, e.g. the Basin-and-Range Province. Our results do not only have important consequences for the interpretation of palaeoseismological records from faults in these regions but also for the evaluation of the future seismicity in regions currently affected by deglaciation like Greenland and Antarctica: shrinkage of the modern ice sheets owing to global warming may ultimately lead to an increase in earthquake frequency in these regions.

Slip rate variations on faults during glacial loading and post-glacial unloading: implications for the viscosity structure of the lithosphere

Abstract: Many active faults in extensional and contractional tectonic settings experienced a slip rate increase after the last glacial period when the volume of nearby glaciers and lakes decreased. This post-glacial slip rate increase is caused by transient stresses that are generated by the unloading-induced rebound and superimposed on the tectonic background stress field. As the latter is different for normal and thrust faults, the response to loading and unloading should depend on the fault type. Here we use finite-element models including a fault in rheologically layered lithosphere to explore the conditions under which both normal and thrust faults experience a post-glacial slip rate increase. The results show that a post-glacial slip rate increase occurs on normal faults if the lower crust is stronger than the lithospheric mantle, whereas thrust faults accelerate if the lower crust is weaker than the lithospheric mantle. These findings imply that the response of faults to mass fluctuations on the Earth's surface may provide constraints on the rheological stratification of the lithosphere. We use our results to make predictions on the viscosity structure of the Basin-and-Range Province and northern Scandinavia, where palaeoseismological data document a pronounced increase in seismicity as a result of post-glacial unloading and rebound.

Slip rate variations on faults in the Basin-and-Range Province caused by regression of Late Pleistocene Lake Bonneville and Lake Lahontan

Late Pleistocene regression of two large pluvial lakes—Lake Bonneville and Lake Lahontan—caused considerable lithospheric rebound in the Basin-and-Range Province, USA. Here, we use finite-element models to show how lake growth and regression affect the temporal and spatial slip evolution on faults near the former lakes. Our results show that fluctuations in the volume of Lake Bonneville caused along-strike slip variations on the Wasatch normal fault, with a pronounced slip rate increase on its northern and central parts during lake regression. The response of normal and strike-slip faults near the ring-shaped Lake Lahontan depends on their location within the rebound area. Faults located in the centre of rebound show a slip rate increase during lake regression, whereas strike-slip faults at the periphery decelerate. All slip rate variations are caused by differential stress changes owing to changing lake levels, regardless of the individual fault response.

Aseismic crustal movement in southern Ryukyu Trench, southwest Japan

[1] Anomalous crustal deformation following the Mw = 7.1, March 31, 2002, Hualien earthquake was observed over 5 years using the global positioning system (GPS) network in the south Ryukyu Islands. The analysis showed an afterslip event at a depth of 30 km on the subducting Philippine Sea plate. The magnitude of the cumulative moment reached 7.4. The released moment of the afterslip exceeded the mainshock itself. The afterslip promoted Coulomb failure stress on the fault of the repeating slow slip events (SSEs) in the vicinity of the afterslip. The increase in the slip rate of the SSEs predicted through the change in the Coulomb failure stress is 13%. This is close to the observed increase in slip rate (19%) after the earthquake. This suggests that the afterslip had accelerated the slip rate of the SSEs after the earthquake.

Three‐dimensional numerical modeling of slip rate variations on normal and thrust fault arrays during ice cap growth and melting

Changes in the volumes of ice caps considerably alter the stress state of the lithosphere by generating a transient signal that is added to the tectonic background stress field. These stress field changes, in turn, affect crustal deformation and in particular the slip behavior of existing faults. Here we use three‐dimensional finite element models to investigate how arrays of normal and thrust faults near a growing and subsequently melting ice cap are influenced in their slip evolution. The results show that regardless of fault dip, both types of faults experience a decrease in their slip rate during ice cap advance and an increase in their slip rate during ice cap retreat if they are located beneath the ice cap. In contrast, faults outside the ice cap that are loaded on their footwall or hanging wall only show the opposite pattern: their slip rate increases during glacial loading and decreases during subsequent unloading. If the load is located along strike of the fault; that is, at one of its tips, the slip behavior of normal and thrust faults is different: The normal fault shows a slip rate increase during unloading, the thrust fault during loading. Our results explain the location and timing of deglaciation‐induced paleoearthquakes in Scandinavia and the contrasting slip histories reported from normal faults in the Basin and Range Province, which are located at different positions relative to the former Yellowstone ice cap. More generally, our findings imply that a uniform slip behavior of faults in formerly glaciated regions should not be expected.

Slip acceleration on normal faults due to erosion and sedimentation — Results from a new three-dimensional numerical model coupling tectonics and landscape evolution

Although it is well accepted that mass redistribution on Earth's surface due to erosion and sedimentation affects the rate of crustal deformation, the influence of surface processes on the slip behaviour of individual faults remains poorly understood. Here we use the new tool CASQUS, which combines landscape evolution modelling with three-dimensional tectonic models, to investigate how erosion and sediment deposition affect fault behaviour in extensional tectonic regimes. A systematic set of experiments with models consisting of an isostatically responding elastic upper crust containing a single normal fault shows that the slip accumulation on the fault is accelerated by erosion and sedimentation. Depending on fault geometry, extension rate and parameters controlling erosion and sediment deposition, the slip rate of the normal fault is up to ~ 15% higher when surface processes are taken into account. The slip acceleration can be explained by an increase in the differential stress caused by erosion of the fault footwall and sedimentation in the hanging wall, which alter the faulting-induced flexure of the crust. We observe a similar slip rate increase in a more complex model of a growing horst bounded by three faults of different length. Our results show that a positive feedback exists between surface processes and tectonics and imply that geologically derived fault slip rates that integrate over several earthquake cycles may contain a contribution from surface processes.