Preseismic Slip Research Articles

Can the Thermal Infrared Radiation Anomalies Reported Before Earthquakes be a Precursor?

Twenty-seven earthquakes in Taiwan with local magnitudes [Formula: see text] and focal depths d = 8.0−215.8[Formula: see text]km were preceded by thermal infrared radiation (TIR) anomalies. The data are taken as an example to investigate the mechanisms of generating the TIR and to examine whether the TIR anomalies can be considered as a precursor or not. Let [Formula: see text] and [Formula: see text] be the largest number of days before forthcoming earthquakes when the anomalies are observed in the day-time and the night-time, respectively. The precursor time, T, for an event, is the larger value of [Formula: see text] and [Formula: see text]. The plots of both T vs. [Formula: see text] and [Formula: see text] vs. [Formula: see text] are scattered. Regardless of two data points with abnormally large [Formula: see text] values, it seems able to recognize a positive correlation between [Formula: see text] and [Formula: see text]. Among the 27 earthquakes, 8 events were proceeded by Rn concentration changes whose precursor times are [Formula: see text] days. For most of the eight events, [Formula: see text] is much longer than either [Formula: see text] or [Formula: see text]. Hence, the model of outflow of gases from the depths to the ground surface for describing the Rn concentration changes cannot interpret the TIR anomalies. Based on rock mechanics, the temperature rise, [Formula: see text], is generated by frictional heating due to preseismic slip. That the TIR anomalies discontinuously appeared before earthquakes and the occurrence times vary for different events is inconsistent with the processes of generation of frictional heating caused by preseismic slip on a few shallow faults in the source areas before forthcoming earthquakes. Since theoretical results and observations are not consistent, the answer to the title of this study is negative.

Extraction of transient signal from GPS position time series by employing ICA

Transient deformation, such as post-seismic slip, slow slip and pre-seismic slip events, is a limited low-frequency deformation that can last for hours to months, in contrast to a sudden slip on a fault caused by earthquakes. Continuous Global Positioning System (CGPS), one of the most common geodetic techniques for continuously monitoring crustal deformation, is capable of capturing transient deformation signals. A critical point in characterizing transient deformation signals is the development of extracting and deciphering transient deformation signals from a huge and messy data set of position time series. Principal Component Analysis (PCA), one of the data-driven methods, has been employed to derive transient deformation signals from position time series combing with Kalman filtering. Independent Component Analysis (ICA) performs well in recovering and separating the sources of observed data, however, it is rarely used in extracting transient deformation signals. We aim to decompose the transient deformation signals from the daily GPS observation deployed in Akutan Island from 2007 to 2015 with the ICA method and obtain the spatiotemporal responses to the source signals of transient deformation. Our results indicate that ICA method can also characterize effectively transient deformation signals spatially and temporally. Additionally, the independent relationship between sources obtained by ICA allows for flexibility in linearly combining different sources.

Poromechanics of stick‐slip frictional sliding and strength recovery on tectonic faults

AbstractPore fluids influence many aspects of tectonic faulting including frictional strength aseismic creep and effective stress during the seismic cycle. However, the role of pore fluid pressure during earthquake nucleation and dynamic rupture remains poorly understood. Here we report on the evolution of pore fluid pressure and porosity during laboratory stick‐slip events as an analog for the seismic cycle. We sheared layers of simulated fault gouge consisting of glass beads in a double‐direct shear configuration under true triaxial stresses using drained and undrained fluid conditions and effective normal stress of 5–10 MPa. Shear stress was applied via a constant displacement rate, which we varied in velocity step tests from 0.1 to 30 µm/s. We observe net pore pressure increases, or compaction, during dynamic failure and pore pressure decreases, or dilation, during the interseismic period, depending on fluid boundary conditions. In some cases, a brief period of dilation is attendant with the onset of dynamic stick slip. Our data show that time‐dependent strengthening and dynamic stress drop increase with effective normal stress and vary with fluid conditions. For undrained conditions, dilation and preseismic slip are directly related to pore fluid depressurization; they increase with effective normal stress and recurrence time. Microstructural observations confirm the role of water‐activated contact growth and shear‐driven elastoplastic processes at grain junctions. Our results indicate that physicochemical processes acting at grain junctions together with fluid pressure changes dictate stick‐slip stress drop and interseismic creep rates and thus play a key role in earthquake nucleation and rupture propagation.

Slow Earthquakes, Preseismic Velocity Changes, and the Origin of Slow Frictional Stick-Slip

Earthquakes normally occur as frictional stick-slip instabilities, resulting in catastrophic failure and seismic rupture. Tectonic faults also fail in slow earthquakes with rupture durations of months or more, yet their origin is poorly understood. Here, we present laboratory observations of repetitive, slow stick-slip in serpentinite fault zones and mechanical evidence for their origin. We document a transition from unstable to stable frictional behavior with increasing slip velocity, providing a mechanism to limit the speed of slow earthquakes. We also document reduction of P-wave speed within the active shear zone before stick-slip events. If similar mechanisms operate in nature, our results suggest that higher-resolution studies of elastic properties in tectonic fault zones may aid in the search for reliable earthquake precursors.

Migration process of very low-frequency events based on a chain-reaction model and its application to the detection of preseismic slip for megathrust earthquakes

In order to reproduce slow earthquakes with short duration such as very low frequency events (VLFs) migrating along the trench direction as swarms, we apply a 3-D subduction plate boundary model based on the slowness law of rate- and state-dependent friction, introducing close-set numerous small asperities (rate-weakening regions) at a depth of 30 km under high pore pressure condition, in addition to a large asperity. Our simulation indicates that swarms of slip events occur repeatedly at the small asperities, and these events are similar to the observed slow earthquake group, especially to VLF, on the basis of the relation between characteristic duration and seismic moment. No slip events occur there without the small asperities, which mean that the close-set numerous small asperities may be one of the necessary conditions for generating the short-duration slow earthquakes such as VLFs. In the preseismic stage of the megathrust earthquakes that occur at the large asperity, the swarms of VLFs have higher migration speeds and higher moment release rate as well as shorter recurrence interval. Thus, monitoring the migration of slow earthquakes may be useful in imaging the preseismic slip of megathrust earthquakes.

Surface displacement of the Mw 7 Machaze earthquake (Mozambique): Complementary use of multiband InSAR and radar amplitude image correlation with elastic modelling

In this paper we investigate the surface displacement related to the 2006 Machaze earthquake using Synthetic Aperture Radar Interferometry (InSAR) and sub-pixel correlation (SPC) of radar amplitude images. We focus on surface displacement measurement during three stages of the seismic cycle. First, we examined the co-seismic stage, using an Advanced SAR (ASAR) sensor onboard the Envisat satellite. Then we investigated the post-seismic stage using the Phase Array L-band SAR sensor (PALSAR) onboard the ALOS satellite. Lastly, we focussed on the inter-seismic stage, prior to the earthquake by analysing the L-band JERS-1 SAR data. The high degree of signal decorrelation in the C-band co-seismic interferogram hinders a correct positioning of the surface rupture and correct phase unwrapping. The post-seismic L-band interferograms reveal a time-constant surface displacement, causing subsidence of the surface at a ∼5cm/yr rate. This phenomenon continued to affect the close rupture field for at least two years following the earthquake and intrinsically reveals a candidate seismogenic fault trace that we use as a proxy for an inversion against an elastic dislocation model. Prior to the earthquake, the JERS interferograms do not indicate any traces of pre-seismic slip on the seismogenic fault. Therefore, slip after the earthquake is post-seismic, and it was triggered by the Machaze earthquake. This feature represents a prominent post-seismic slip event rarely observed in such a geodynamic context.

Complex kinematic rupture of the Mw 5.9, 1999 Athens earthquake as revealed by the joint inversion of regional seismological and SAR data

SUMMARY Slip distributions of the moderate magnitude (Mw 5.9), 1999 Athens earthquake, inverted from surface waves and interferometric Synthetic Aperture Radar (SAR) images, show very different characteristics. The robustness analysis proposed in this study, confirms the discrepancy between the well-constrained features of each individual solution. Irrespective of the hypotheses we made (data/modeling errors, slow deformation, post- or pre-seismic slip), the joint inversion of the two data sets led to a complex and heterogeneous rupture model. This model is characterized by a short rise time (< 5s )slip patch centred on the hypocentre, extending bilaterally up to 4 km depth and down to 17 km and releasing approximately 70 per cent of the total moment. Located further to the WNW and releasing the remaining 30 per cent of the total moment, a long rise time slip patch extends from 8 to 17 km depth. If the short rise time slip patch propagated above and below the brittle zone delineated by the aftershocks, the long rise time slip patch (slow deformation) appears to be mostly confined below the brittle zone. This unified model satisfies the analysis of the seismic and geodetic slip distributions as well as the location of the aftershock sequence and attests to the diversity of the crustal response even for moderate size faults.

A possible model for large preseismic slip on a deeper extension of a seismic rupture plane

I develop a numerical model for preseismic slip and episodic aseismic slip events (slow earthquakes) on a deeper extension of a seismogenic plate interface, using a rate- and state-dependent friction law. The deep preseismic slip and episodic slow slip were indicated by models based on geodetic observations, though they cannot be explained by common rate- and state-dependent laws. I investigate whether this incongruity can be removed by including use of additional known constraints on the frictional property. The steady-state friction on a model fault is taken to be velocity weakening at low velocities and velocity strengthening at high velocities. The transition velocity from velocity-weakening friction to velocity-strengthening is assumed to be the seismic slip velocity at shallow seismic depths and decreases with depth at deeper parts. Simulation results for a 2D model of interplate earthquakes at a subduction zone are as follows: (1) During an interseismic period between successive large earthquakes at shallow seismogenic depths, some episodic aseismic slip events with durations of a few years occur on the plate interface just below the seismogenic depths. (2) Preseismic slip occurs at nearly the same location where the episodic aseismic slip events occur. These may explain some characteristics of observed preseismic slip of the 1944 Tonankai earthquake ( M=7.9) along the Nankai trough, central Japan, and episodic aseismic slip events in the same area.

Pre‐seismic slip on the 26 September 1997, Umbria‐Marche Earthquake fault? Unexpected clues from the analysis of 1951–1992 elevation changes

We studied 1951–1992 elevation changes recorded by a first order leveling line that intercepts the surface projection of the 26 Sep. 1997, Mw 6.0, Umbria‐Marche earthquake causative fault. The line documents 1951–1992 localized subsidence along a 12 km section above the fault. We calculated the expected 1997 coseismic elevation changes along the line using standard dislocation modeling and found that their trend has an amplitude three times larger than the trend of the observed pre‐1997 signal but with a similar shape. We suggest that this signal is the result of 10 cm of pre‐1992 slip along the northernmost 5 km of the 1997 earthquake fault, where coseismic slip was found to be less than the average estimated for the entire fault. This result implies unusually fast slip along this section of the fault and may suggest slip acceleration in preparation for the impending failure.

Earthquake nucleation on model faults with rate‐ and state‐dependent friction: Effects of inertia

Laboratory studies suggest that earthquake nucleation involves a transition from quasi‐static slip when inertial effects are negligible to inertia‐driven, dynamic motion. This transition occurs via quasi‐dynamic motion, during which the effects of inertia become increasingly important. The characteristics of this transition, which depend on frictional properties of the fault, determine the observability of earthquake nucleation by seismic, geodetic, or other means. By investigating the role of inertia during nucleation, we obtain a quantitative definition of the limiting velocity Vin, which marks the end of quasi‐dynamic motion and the onset of instability. For reasonable friction parameters and fault widths, we obtain estimates of Vin for crustal faults. To study the roles of inertia, stiffness, and friction parameters on preseismic motion, we simulate triggered instabilities in a one‐dimensional model of a homogeneous fault, with rate and state variable friction. In most of our simulations, triggering is achieved by applying a stress perturbation to an initially creeping fault under steady state friction. We also investigate triggering on faults which are initially locked and overstressed compared to their nominal frictional strength, due to time‐dependent healing. We study the amount, Up, and duration, Tp, of preseismic slip as a function of system mass m and other model parameters. For crustal faults, we interpret the relevant mass as a product of density and fault width and find that wider fault zones result in smaller Up and larger Tp. Both Up and Tp are proportional to the system stiffness K, the characteristic slip distance Dc, and the friction constitutive parameter a and inversely proportional to the size of the triggering event. We find greater Up and Tp for constitutive laws which allow strengthening at zero velocity, compared to laws that require slip or a combination of slip and aging for state evolution. In contrast to quasi‐static modeling, our simulations suggest a minimum stress perturbation criterion for instability, which may be interpreted in terms of a strain threshold for triggered seismicity.

Near‐field high resolution strain measurements prior to the October 18, 1989, Loma Prieta Ms 7.1 Earthquake

High resolution strain recordings were made in deep boreholes throughout California prior to, during, and following, the October 18, 1989, Ms 7.1 Loma Prieta earthquake. The nearest dilational strainmeters (sensitivity 1010) and 3‐component tensor strainmeters (sensitivity 10−9) were 37 km to 42 km, respectively, from the main shock. High quality data, including details of strain offsets, were recorded on both instruments through the earthquake. These data have been searched for indications of short‐, intermediate‐, and long‐term strain redistribution and/or fault slip that might have indicated imminent rupture. Short‐ and intermediate‐term changes in both tensor strain and dilational strain (≤, several nanostrain, if any) during the minutes to months before the earthquake are at least 1000 times smaller than that generated by the earthquake itself. If short‐term preseismic slip did occur at the nucleation point of the earthquake during the previous week, and if the type of slip is similar to that during the earthquake, its moment could not be more than 1024 dyne‐cm. Stated another way, slip equivalent to that expected for a M 5.3 earthquake could have occurred in the hypocentral region without the strainmeters detecting it at these distances and azimuthal positions. Long‐term changes appear to have occurred in mid 1988 and mid 1989. These changes were both followed by ML 5 earthquakes in the hypocentral region on June 27, 1988, and August 8, 1989, respectively, and, since they correspond approximately to changes in geodetic strain rate over the epicenter, may indicate precursory strain redistribution in the epicentral region. Minor postseismic strain recovery (≈ 14%) occurred in the month following the main shock.

Idealized models of fault behavior prior to dynamic rupture

We present a theoretical model, based on fracture mechanics concepts, of the behavior of an earthquake source prior to the occurrence of the earthquake, to understand under what conditions precursory slip may occur on a fault and to determine realistic initial conditions for the dynamic problem of faulting. We consider a two-dimensional fault consisting of in-plane periodic shear cracks and unbroken zones in an infinite, homogeneous elastic medium. Between the cracks of length 2a and the unbroken zones are “intermediate” zones in which the stress drop occurs when a “critical shear displacement” (CSD) is reached (Panasyuk-Dugdale model) at the crack tip. The unbroken zones can also be interpreted in terms of friction as regions where the stress is lower than the static frictional stress, so that our model can be interpreted from the point of view of fracture or friction. Let the period of this system be 2d. As the load at infinity is slowly increased, the intermediate zones grow quasi-statically with a small amount of associated slip in the broken regions of the fault plane. It is found that when the cracks are very small or very large or the CSD is large, the intermediate zones will coalesce before the CSD is reached, i.e., the entire fault is ruptured and additional preseismic slip occurs. The initial conditions for dynamic rupture occurring at a later time on the fault is then a stress condition. Thus, for the initial stages of the dynamic problem (not studied here) one need not solve a mixed boundary value problem but only the much simpler stress boundary problem. The rupture velocity of the dynamic rupture on such a fault which is entirely broken, may have any value up to the P -wave velocity, in principle. The average slip on the fault at the point of coalescence increases with crack size from zero at zero crack length up to a/d ≃ 0.67 and then decreases to zero at a/d = 1. The displacement distribution on the crack and the shear stress distribution around the crack as a function of increasing load and increasing crack size a/d are studied. It is shown that strain accumulation occurs not only at the ends of a Griffith crack but also in broad regions off the crack in the normal direction. Corresponding to the unbroken zone, there is a similar zone but of strain release off the crack. This zone becomes more and more pronounced for large cracks and high loads. For very long cracks, the increase in shear stress off the crack becomes very very small but the decrease off the initially unbroken zone becomes very pronounced. Interaction between cracks is correctly accounted for in our method.

Modeling of rock friction: 2. Simulation of preseismic slip

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.

Preseismic slip in a large scale friction experiment : Dieterich, J H; Barber, D W; Conrad, G Proc 19th US Symposium on Rock Mechanics, Stateline, Nevada, 1–3 May 1978, V1, P110–117. Publ Reno: University of Nevada, 1978

Preseismic slip in a large scale friction experiment : Dieterich, J H; Barber, D W; Conrad, G Proc 19th US Symposium on Rock Mechanics, Stateline, Nevada, 1–3 May 1978, V1, P110–117. Publ Reno: University of Nevada, 1978

Preseismic fault slip and earthquake prediction

It is proposed that preseismic fault creep may be the underlying process that is responsible for observations of earthquake precursors. The assertion that fault creep precedes earthquakes is supported by evidence from at least some earthquakes and by analogy with detailed laboratory observations. Laboratory observations of stick slip reveal that at least two stages of preseismic slip are an intrinsic part of the process leading to seismic slip on preexisting faults with inhomogeneous stress or strength. During the slowly propagating first stage of creep it is assumed that the length of the creeping fault segment is proportional to the source length of the subsequent earthquake. The data giving the well‐known relationship between precursor time and earthquake magnitude are closely satisfied if the rate of propagation of the first stage of creep is independent of fault length. Long‐term precursors may arise because of stress‐strain variations during the first stage of fault creep. Observations of short‐term precursors immediately prior to earthquakes may be related to the second short‐lived state of preseismic fault slip seen in stick slip experiments.

Anomalous tilt preceding the Hollister earthquake of November 28, 1974

The occurrence of a magnitude 5.2 earthquake on November 28, 1974, near Hollister in central California, provided an excellent opportunity to test the potential of a prototype tiltmeter array as a predictive tool. Tilt perturbations on instruments near the epicenter were evident about 36 days before the earthquake and coincided with a magnetic field anomaly reported in a companion paper. The anomalous tilts systematically changed with time, reaching values as great as 7 μrad. These data are interpreted in terms of a preseismic and postseismic slip mechanism involving interaction between the San Andreas and other faults in the region, where slip on one results in a sympathetic slip on others.