Postseismic Motion Research Articles

Analysis of October 23 (Mw 7.2) and November 9 (Mw 5.6), 2011 Van Earthquakes Using Long-Term GNSS Time Series

The eastern Anatolia provides one of the best examples of an area of rapid deformation and intense contraction that is the consequence of an active continental collision between the Arabian and Eurasian plates leading to large and devastating earthquakes. The latest evidence of the active tectonism in the region is revealed by two remarkable seismic events; Van-Tabanli (Mw 7.2, October 23, 2011) and Van-Edremit (Mw 5.6, November 9, 2011) earthquakes. The study of the earthquake cycle and observation of geodetic and seismic deformation in this region is very important to hazard assessments. In this study, the inter-seismic, co-seismic, and post-seismic movements caused by the above-mentioned earthquakes were investigated using the time series of 2300 days of Global Navigation Satellite Systems (GNSS) observations of the local stations selected from the network of the Continuously Operating Reference Stations, Turkey (CORS-TR). For the inter-seismic period, approximately 1100 daily data were obtained from 21 CORS-TR stations (prior to the earthquakes between October 1, 2008 and October 23, 2011) and evaluated using the GAMIT/GLOBK software. The behaviour of these stations was investigated by processing 1 Hz data from the GNSS stations during the earthquakes on the GAMIT/TRACK software. In addition to October 23 and November 9, the GNSS data on one day before and after the earthquakes was assessed to determine co-seismic deformations. During the October 23 earthquake, hanging-wall deformation of about 60 mm was detected in the SW direction at the MURA station. However, at the VAAN station, deformation of 200 mm (value predicted by time series) was observed in the footwall block in the NW direction. There were not any significant changes at the stations during the November 9 earthquake. For the post-seismic period, the GNSS data from 2012 to 2015 was evaluated. According to the observations, post-seismic deformation continued at the stations close to the epicenter of the earthquake.

Post-seismic motions after the 2006–2007 Simushir earthquakes at different stages of the seismic cycle

We analyzed long-term satellite geodesic observations after the Simushir earthquakes of 2006–2007. Application of a key model of the structure of the island arc regions combined with a model of nonstationary convective system in the upper mantle allowed us to find a consistent explanation of the motion of the Earth’s surface and distinguish the segments of the island arc at different stages of the seismic cycle.

Global Positioning System Data Collection, Processing, and Analysis Conducted by the U.S. Geological Survey Earthquake Hazards Program

ABSTRACT The U.S. Geological Survey Earthquake Science Center collects and processes Global Positioning System (GPS) data throughout the western United States to measure crustal deformation related to earthquakes and tectonic processes as part of a long‐term program of research and monitoring. Here, we outline data collection procedures and present the GPS dataset built through repeated temporary deployments since 1992. This dataset consists of observations at ∼1950 locations. In addition, this article details our data processing and analysis procedures, which consist of the following. We process the raw data collected through temporary deployments, in addition to data from continuously operating western U.S. GPS stations operated by multiple agencies, using the GIPSY software package to obtain position time series. Subsequently, we align the positions to a common reference frame, determine the optimal parameters for a temporally correlated noise model, and apply this noise model when carrying out time‐series analysis to derive deformation measures, including constant interseismic velocities, coseismic offsets, and transient postseismic motion.

The seismic interactions and spatiotemporal evolution of seismicity following the October 23, 2011 Mw 7.1 Van, Eastern Anatolia, earthquake

We studied the mechanisms and spatiotemporal distribution of aftershocks of the Mw 7.1 Van earthquake, in Eastern Turkey. The Van earthquake occurred on an E-W trending thrust fault, in a region under N-S compression due to the convergence of the Arabian plate toward Eurasia. We relocated the seismicity by combining catalogs from two agencies and studied the source mechanisms of the Mw 3.5–5.6 aftershocks using regional body and surface waves. In addition to the aftershocks with thrust mechanism on the mainshock fault, we identified three clusters with strike-slip activity. Two of the clusters are on the left-lateral faults perpendicular to the mainshock fault and are located at the lateral termination of the co-seismic rupture in each direction. Both western and eastern strike-slip clusters were triggered within the first few hours following the mainshock. They were initiated very close to the mainshock rupture plane and propagated away toward the south and north respectively. These two dominantly strike-slip zones are connected to the mainshock fault at a depth of 15km and possibly determined the lateral extent of the 2011 rupture. This system of two bounding left lateral faults with a thrust fault in between is overall consistent with the N-S convergent tectonic regime in the region. The complex geometry explains unexpected post-seismic motion at a GPS site and can be used to improve the post-seismic slip estimate of the earthquake. The third strike-slip cluster with 17days delay occurred on an E-W trending right-lateral fault and 40km on the south of the mainshock. The three activated faults have experienced Coulomb stress increase due to co-seismic rupture. In addition, most of the seismicity has occurred in regions that experienced Coulomb stress increase.

Recent geodynamics of the Kuril subduction zone

The collected GPS/GLONASS data allow us to reveal new information on the recent geodynamics of the Kuril Island arc. The maximum deformation stress accumulates in the southern and northern parts of the study area, while a long fading transition process of postseismic motions is observed in the central segment of the Kuril arc as a result of the 2006–2007 great Simushir earthquakes of Mw = 8.3 and Mw = 8.1. We have succeeded in revealing the recent interplate coupling geometry of the Pacific and the North American lithospheric plates and also in estimating the seismic potential of different segments of the Kuril subduction zone.

Investigation of Post-seismic and Inter-seismic Displacement Field Following 2003 Bam Earthquake in Iran Based on PS-InSAR Technique

In this paper, Bam post-seismic deformations during 7 years after earthquake have been extracted using persistent scatterer interferometry technique. The results illustrate that the maximum amount of uplift and subsidence displacements along line of sight direction during 2004–2010 after the earthquake are 4.5 ± 0.5 and − 4.3 ± 0.5 cm, respectively. The results of displacement field indicate that an exponential function with the relaxation time of 2.5 years can be fitted to the corresponding process. The estimated inter-seismic slip value by the inversion of SAR line-of-sight data after relaxation time is 6.35 ± 0.05 mm. Mechanical time dependent processes in the post-seismic relaxation typically rely on models of poroelastic rebound, afterslip fault dilatancy recovery and viscoelastic relaxation to explain surface displacements field. The time series are inverted for the afterslip distribution on an extension of the co-seismic rupture. The estimated post-seismic slip value is 20.45 ± 0.38 cm. Most of the post-seismic displacement field can be explained in terms of fault slip. The results of post-seismic motion modeling indicate that the poroelastic rebound can be detected using the line-of-sight data and the effect of viscoelastic relaxation in post-seismic displacement is negligible.

Transient crustal movement in the northern Izu–Bonin arc starting in 2004: A large slow slip event or a slow back-arc rifting event?

The Izu–Bonin arc lies along the convergent boundary where the Pacific Plate subducts beneath the Philippine Sea Plate. Horizontal velocities of continuous Global Navigation Satellite System stations on the Izu Islands move eastward by up to ~1cm/year relative to the stable part of the Philippine Sea Plate suggesting active back-arc rifting behind the northern part of the arc. Here, we report that such eastward movements transiently accelerated in the middle of 2004 resulting in ~3cm extra movements in 3years. We compare three different mechanisms possibly responsible for this transient movement, i.e. (1) postseismic movement of the 2004 September earthquake sequence off the Kii Peninsula far to the west, (2) a temporary activation of the back-arc rifting to the west dynamically triggered by seismic waves from a nearby earthquake, and (3) a large slow slip event in the Izu–Bonin Trench to the east. By comparing crustal movements in different regions, the first possibility can be shown unlikely. It is difficult to rule out the second possibility, but current evidence support the third possibility, i.e. a large slow slip event with moment magnitude of ~7.5 may have occurred there.

The 2012 August 27Mw7.3 El Salvador earthquake: expression of weak coupling on the Middle America subduction zone

Subduction zones exhibit variable degrees of interseismic coupling as resolved by inversions of geodetic data and analyses of seismic energy release. The degree to which a plate boundary fault is coupled can have profound effects on its seismogenic behaviour. Here we use GPS measurements to estimate co- and post-seismic deformation from the 2012 August 27, Mw7.3 megathrust earthquake offshore El Salvador, which was a tsunami earthquake. Inversions of estimated coseismic displacements are in agreement with published seismically derived source models, which indicate shallow (<20 km depth) rupture of the plate interface. Measured post-seismic deformation in the first year following the earthquake exceeds the coseismic deformation. Our analysis indicates that the post-seismic deformation is dominated by afterslip, as opposed to viscous relaxation, and we estimate a post-seismic moment release one to eight times greater than the coseismic moment during the first 500 d, depending on the relative location of coseismic versus post-seismic slip on the plate interface. We suggest that the excessive post-seismic motion is characteristic for the El Salvador–Nicaragua segment of the Central American margin and may be a characteristic of margins hosting tsunami earthquakes.

Coseismic and Early Postseismic Deformation of the 5 January 2013 Mw 7.5 Craig Earthquake from Static and Kinematic GPS Solutions

Static (low‐rate, 30 s) and kinematic (high‐rate, 1 s) Global Positioning System solutions are employed to investigate the near‐field coseismic and early postseismic deformation associated with the 5 January 2013 Craig M w 7.5 earthquake. Based on the static solutions, the coseismic slip distribution has an average slip of ∼6 m, a geodetic moment M of 1.5×1020 N·m, and a magnitude M w of 7.4. A comparison of the static and kinematic results indicates that early (first 4 days) postseismic deformation was small compared to the coseismic deformation. The postseismic transient can be characterized by a logarithmic decay function with an average decay time constant of about 56 days. Substantial postseismic deformation is observed over the first ∼1.6 yrs of the earthquake and can be explained by afterslip on an adjacent segment of the fault to the southeast of the main coseismic rupture. Additional study will be needed to confirm whether afterslip is indeed the dominant mechanism causing postseismic motions or if another mechanism is also active. Online Material: Figures showing high‐rate Global Positioning System time series and model fits for selected sites.

Viscoelastic relaxation following subduction earthquakes and its effects on afterslip determination

AbstractAfterslip is commonly thought to be the controlling process in postseismic deformation immediately following a great megathrust earthquake and is usually inferred from geodetic observations using purely elastic models. However, observed motion reversal of the near‐trench area right after the 2011 Mw 9 Tohoku‐oki earthquake demonstrates the dominance of viscoelastic relaxation of coseismically induced stresses. To understand the importance of incorporating viscoelasticity in afterslip determination, we employ biviscous Burgers mantle rheology and use finite element models to explore how viscoelastic relaxation in short‐term postseismic deformation is controlled by various geometrical and rheological factors. Our results indicate that immediately after large megathrust earthquakes (Mw &gt; 8.0), viscoelastic deformation should always cause opposing motion of inland and trench areas and subsidence around landward termination of the rupture, although the rate of such postseismic motion depends on local conditions such as the age and hence thickness of the slab and transient mantle viscosity values. While elastic models may be adequate for afterslip estimation for earthquakes of Mw &lt; 7.5, neglect of viscoelasticity for larger events leads to overestimate of afterslip downdip of the rupture and underestimate of afterslip at shallower depths. Reassessing shallow afterslip following the 2005 Mw 8.7 Nias earthquake using 2‐D viscoelastic models suggests that the actual afterslip may be greater than that estimated using an elastic model by more than 50%. Similarly, interpreting trenchward motion of some seafloor GPS sites following the Tohoku‐oki earthquake using a viscoelastic model suggests large shallow afterslip outside of the main rupture area.

Crustal deformation on the Chinese mainland during 1998–2014 based on GPS data

This study focuses on resolving moderate amounts of crustal motion at the continental scale based on a large volume of global positioning system (GPS) data during 1998–2014. A state-of-the-art GPS processing strategy was used to resolve position time series and velocities from carrier beat phases for all available data. Position time series were closely analyzed to estimate linear constant, coseismic displacements, postseismic motions, and other parameters. We present coseismic offsets inferred from the GPS data for the 2010 Yushu and 2014 Yutian earthquakes, and also illustrate transient postseismic motions following the 2001 Kokoxili, 2008 Wenchuan, and 2011 Tohoku-Oki earthquakes. Since not all GPS position time series dominated by postseismic motions can be modeled and corrected reasonably, we present contemporary horizontal velocities from 2009 to 2014 for campaign stations and from 1998 to 2014 for continuous stations, irrespective of postseismic deformations. Our study concludes that we need to accumulate observations over a greater duration and apply accurate postseismic modeling to correct for transient displacement in order to resolve reasonable interseismic velocity.

Coseismic and postseismic motion of a landslide: Observations, modeling, and analogy with tectonic faults

AbstractWe document the first time series of a landslide reactivation by an earthquake using continuous GPS measurements over the Maca landslide (Peru). Our survey shows a coseismic response of the landslide of about 2 cm, followed by a relaxation period of 5 weeks during which postseismic slip is 3 times greater than the coseismic displacement itself. Our results confirm the coseismic activation of landslides and provide the first observation of a postseismic displacement. These observations are consistent with a mechanical model where slip on the landslide basal interface is governed by rate and state friction, analogous to the mechanics of creeping tectonic faults, opening new perspectives to study the mechanics of landslides and active faults.

Evidence of viscoelastic deformation following the 2011 Tohoku‐Oki earthquake revealed from seafloor geodetic observation

AbstractThe GPS/acoustic seafloor positioning has detected significant postseismic movements after the 2011 Tohoku‐Oki earthquake (M9.0), just above the source region off the Pacific coast of eastern Japan. In contrast to the coastal Global Navigation Satellite Systems sites where trenchward‐upward movements were reported, the offshore sites above the main rupture zone in the northern part of the source region exhibit landward displacements of tens of centimeters with significant subsidence from almost 3 years of repeated observations. At the sites above around the edge of the main rupture zone, smaller amount of trench‐normal movements was found. Although the terrestrial movements were reasonably interpreted by afterslip beneath the coastal area, these offshore results are rather consistent with effects predicted from viscoelastic relaxation in the upper mantle, providing definitive evidence of its occurrence. On the other hand, the results in the southern part of the source region imply superposition of effects from viscoelastic relaxation and afterslip.

Contemporary deformation in the Kashmir–Himachal, Garhwal and Kumaon Himalaya: significant insights from 1995–2008 GPS time series

We present new insights on the time-averaged surface velocities, convergence and extension rates along arc-normal transects in Kumaon, Garhwal and Kashmir–Himachal regions in the Indian Himalaya from 13 years of high-precision Global Positioning System (GPS) time series (1995–2008) derived from GPS data at 14 GPS permanent and 42 campaign stations between \(29.5{-}35^{\circ }\hbox {N}\) and \(76{-}81^{\circ }\hbox {E}\). The GPS surface horizontal velocities vary significantly from the Higher to Lesser Himalaya and are of the order of 30 to 48 mm/year NE in ITRF 2005 reference frame, and 17 to 2 mm/year SW in an India fixed reference frame indicating that this region is accommodating less than 2 cm/year of the India–Eurasia plate motion (\({\sim }4~\hbox {cm/year}\)). The total arc-normal shortening varies between \({\sim }10{-}14~\hbox {mm/year}\) along the different transects of the northwest Himalayan wedge, between the Indo-Tsangpo suture to the north and the Indo-Gangetic foreland to the south indicating high strain accumulation in the Himalayan wedge. This convergence is being accommodated differentially along the arc-normal transects; \({\sim } 5{-}10~\hbox {mm/year}\) in Lesser Himalaya and 3–4 mm/year in Higher Himalaya south of South Tibetan Detachment. Most of the convergence in the Lesser Himalaya of Garhwal and Kumaon is being accommodated just south of the Main Central Thrust fault trace, indicating high strain accumulation in this region which is also consistent with the high seismic activity in this region. In addition, for the first time an arc-normal extension of \({\sim }6~\hbox {mm/year}\) has also been observed in the Tethyan Himalaya of Kumaon. Inverse modeling of GPS-derived surface deformation rates in Garhwal and Kumaon Himalaya using a single dislocation indicate that the Main Himalayan Thrust is locked from the surface to a depth of \({\sim }15{-}20~\hbox {km}\) over a width of 110 km with associated slip rate of \({\sim }16{-}18~\hbox {mm/year}\). These results indicate that the arc-normal rates in the Northwest Himalaya have a complex deformation pattern involving both convergence and extension, and rigorous seismo-tectonic models in the Himalaya are necessary to account for this pattern. In addition, the results also gave an estimate of co-seismic and post-seismic motion associated with the 1999 Chamoli earthquake, which is modeled to derive the slip and geometry of the rupture plane.

Crustal Deformation Associated with the 2011 Tohoku-Oki Earthquake: An Overview

The 2011 Tohoku-oki earthquake generated large displacements in and around the Japanese islands that were detected by the nationwide GPS network, sea-floor geodetic surveys, and space-borne radars. The east-west extension exerted on the Japanese islands by this event induced inland events of Mw6 or larger earthquakes. Coseismic subsidence of up to 1 m was observed along the coast where subsidence was found during the interseismic period. This observation contradicts expectations based on the concept of the recurrence of inter-plate earthquakes. Therefore, postseismic motions or other large events are expected to resolve this paradox.

Effects of lithospheric viscoelastic relaxation on the contemporary deformation following the 1959 Mw 7.3 Hebgen Lake, Montana, earthquake and other areas of the intermountain seismic belt

The 1959 Mw 7.3 Hebgen Lake, MT, normal‐faulting earthquake occurred in an extensional stress regime near the Yellowstone volcanic field. Time‐dependent crustal deformation data following this major earthquake were acquired by precise trilateration and GPS surveys from 1973 to 2000 around the Hebgen Lake fault zone. Modeling the changes of baseline lengths across and near the fault reveals a lateral variation of transient rheology, in which the lithosphere is stronger near the Hebgen Lake fault zone than in the vicinity of the Yellowstone volcano system. The models also imply that the lower crust is stronger than the upper mantle, in agreement with results from studies of postseismic and post‐lake‐filling relaxations (&lt;~100 years). In addition, evaluations of the postseismic motion produced by the Hebgen Lake and the 1983 Mw 6.9 Borah Peak, ID, earthquakes indicate that horizontal transient motion of up to ~1 mm/yr contribute significantly to the contemporary regional crustal deformation near the epicentral areas. For the eastern Basin and Range, ~500 km south of the Hebgen Lake fault, similar rheologic models were derived from the observed uplift associated with the Lake Bonneville rebound and were used to evaluate the postseismic deformation associated with six most recent paleoearthquakes of the Wasatch fault zone and three M ≥ 5.6 historic earthquakes of northern Utah. The results show ≤0.1 mm/yr of horizontal postseismic motion at present time that are within the horizontal uncertainties of continuous GPS velocity from the Basin and Range and significantly smaller than the contemporary extension of 1–3 mm/yr in the Wasatch Front.

Crustal Motion Models Developed for Version 3.2 of the Horizontal Time-Dependent Positioning Utility

The Horizontal Time-Dependent Positioning (HTDP) software allows users to transform positional coordinates across time and between spatial reference frames. To provide this capability, the software includes numerical models for estimating interseismic horizontal crustal velocities in and around the United States, as well as numerical models for estimating the displacements associated with major (magnitude > 6.0) earthquakes in these same areas. Version 3.2 of HTDP was released in August 2012. This HTDP version introduces: (a) an improved model for estimating interseismic horizontal velocities in Alaska, (b) a model for estimating the postseismic motion associated with the M7.9 Denali Fault earthquake that occurred in central Alaska on November 3, 2002, and (c) an improved model for estimating interseismic horizontal velocities in the region of the conterminous United States, which is located east of longitude 107°W. The development and nature of these new models are discussed in this paper.

Postseismic motion after the 2001 MW 7.8 Kokoxili earthquake in Tibet observed by InSAR time series

On November 14th 2001, a Mw 7.8 earthquake occurred in the Kokoxili region of northern Tibet. The earthquake ruptured more than 400 km along the western part of the Kunlun fault with a maximum of 8 m left‐lateral slip. In this paper, we use a multitemporal Interferometric SAR (InSAR) time series technique to map the postseismic motion following the large Kokoxili event. SAR data from Envisat descending orbits along five adjacent tracks covering almost the entire ruptured fault length are used to calculate the displacement time series for a period between 2 and 6 years after the earthquake. A peak‐to‐trough signal of 8 cm in the radar line of sight is observed during the period between 2003 and 2008. Two different mechanisms are employed to explain the observed surface displacements, namely afterslip and viscoelastic relaxation. The observations inverted for afterslip on and below the coseismic rupture plane shows that the maximum slip in the afterslip model is 0.6 m. The position of the maximum postseismic slip is located in the middle of two relatively high coseismic slip patches, which suggests that afterslip is a plausible mechanism. Models of viscoelastic stress relaxation in a Maxwell half‐space give a best fitting viscosity for the mid‐to‐lower crust of 2–5 × 1019 Pa s, and the principal postseismic relaxation process is due to viscous flow in the lower crust to upper mantle. However, the InSAR observations are incapable of distinguishing between localized (afterslip) and distributed (viscoelastic relaxation) deformation. And the lowest misfits are produced by mixed models of viscoelastic relaxation in the mantle below 70 km and afterslip in the crust. Modeling of viscoelastic relaxation in a Maxwell half‐space, and also a mixed mechanism model, enables us to place an effective viscosity of 2 × 1019 Pa s on the lower crust to mantle of northern Tibet.

A unified analysis of crustal motion in Southern California, 1970-2004: The SCEC crustal motion map

[1] To determine crustal motions in and around southern California, we have processed and combined trilateration data collected from 1970 to 1992, VLBI data from 1979 to 1992, and GPS data from 1986 to 2004: a long temporal coverage required in part by the occurrence of several large earthquakes in this region. From a series of solutions for station positions, we have estimated interseismic velocities, coseismic displacements, and postseismic motions. Within the region from 31°N to 38°N. and east to 114°W, the final product includes estimated horizontal velocities for 1009 GPS, 190 trilateration, and 16 VLBI points, with ties between some of these used to stabilize the solution. All motions are relative to the Stable North American Reference Frame (SNARF) as realized through the velocities of 20 GPS stations. This provides a relatively dense set of horizontal velocity estimates, with well-tested errors, for the past quarter century over the plate boundary from 31°N to 36.5°N. These velocities agree well with those from the Plate Boundary Observatory, which apply to a later time period. We also estimated vertical velocities, 533 of which have errors below 2 mm/yr. Most of these velocities are less than 1 mm/yr, but they show 2–4 mm/yr subsidence in the Ventura and Los Angeles basins and in the Salton Trough. Our analysis also included estimates of coseismic and postseismic motions related to the 1992 Landers, 1994 Northridge, 1999 Hector Mine, and 2003 San Simeon earthquakes. Postseismic motions increase logarithmically over time with a time constant of about 10 days, and generally mimic the direction and relative amplitude of the coseismic offsets.

Integration of InSAR Time-Series Analysis and Water-Vapor Correction for Mapping Postseismic Motion After the 2003 Bam (Iran) Earthquake

Atmospheric water-vapor effects represent a major limitation of interferometric synthetic aperture radar (InSAR) techniques, including InSAR time-series (TS) approaches (e.g., persistent or permanent scatterers and small-baseline subset). For the first time, this paper demonstrates the use of InSAR TS with precipitable water-vapor (InSAR TS + PWV) correction model for deformation mapping. We use MEdium Resolution Imaging Spectrometer (MERIS) near-infrafred (NIR) water-vapor data for InSAR atmospheric correction when they are available. For the dates when the NIR data are blocked by clouds, an atmospheric phase screen (APS) model has been developed to estimate atmospheric effects using partially water-vapor-corrected interferograms. Cross validation reveals that the estimated APS agreed with MERIS-derived line-of-sight path delays with a small standard deviation (0.3-0.5 cm) and a high correlation coefficient (0.84-0.98). This paper shows that a better TS of postseismic motion after the 2003 Bam (Iran) earthquake is achievable after reduction of water-vapor effects using the InSAR TS + PWV technique with coincident MERIS NIR water-vapor data.