GPS Measurements Of Crustal Deformation Research Articles

Importance of continuous monitoring GPS permanent station at Multi-Parametric Geophysical Observatory (MPGO), IMPHAL, Manipur (India)

GPS measurements are precise enough to allow a determination of tectonic motion within a few years. This can be made using a network of permanent stations, dynamically defined, using an inertial reference frame that moves with the geo-center. Comparing the position of these points over time, it’s possible to compute the velocity and direction of the plate motion. The goal of this work is to describe the hypothetical tectonic motion using a network of GPS permanent stations located approximately in the center of Imphal Valley. We report data processing results of GPS measurements of crustal deformation at Imphal, Manipur. The results suggest that the site of Imphal valley is not located on the Indian plate. The site is actually located on the Burma plate. Keywords: GPS, Crustal deformation, Imphal Valley, MPGO.

GPS measurements of crustal deformation across the southern Arava Valley section of the Dead Sea Fault and implications to regional seismic hazard assessment

Detailed analysis of crustal deformation along the southern Arava Valley section of the Dead Sea Fault is presented. Using dense GPS measurements we obtain the velocities of new near- and far-field campaign stations across the fault. We find that this section is locked with a locking depth of 19.9 ± 7.7 km and a slip rate of 5.0 ± 0.8 mm/yr. The geodetically determined locking depth is found to be highly consistent with the thickness of the seismogenic zone in this region. Analysis of instrumental seismic record suggests that only ~1% of the total seismic moment accumulated since the last large event occurred about 800 years ago, was released by small to moderate earthquakes. Historical and paleo-seismic catalogs of this region together with instrumental seismic data and calculations of Coulomb stress changes induced by the 1995 Mw 7.2 Nuweiba earthquake suggest that the southern Arava Valley section of the Dead Sea Fault is in the late stage of the current interseismic period.

Continuous GPS measurements of crustal deformation in Garhwal-Kumaun Himalaya

We report GPS measurements of crustal deformation from five continuous sites in the Garhwal Kumaun Himalaya. The motion at these sites confirms strain accumulation on the Main Himalayan Thrust (MHT) under the Outer and Lesser Himalaya with a slip deficit rate of 18 mm/year over a width of ∼100 km. Apart from secular plate motion, these sites also exhibit seasonal variations. We model these seasonal variations using the global models of atmospheric and hydrological loads. The influence of these loads is maximum in the vertical component which decreases in the north and then in the east component. All the four sites in the Himalayan region and a site at Delhi show consistency between the observed seasonal variations with that predicted by the model. However, the annual variations in the horizontal component of displacement time series at BDRI (Badrinath) GPS site are not consistent with the predictions which could be due to local site conditions.

InSAR and GPS measurements of crustal deformation due to seasonal loading of Tehri reservoir in Garhwal Himalaya, India

Author(s): Gahalaut, VK; Yadav, RK; Sreejith, KM; Gahalaut, K; Burgmann, R; Agrawa, R; Sati, SP; Bansal, A | Abstract: We report unique observations of crustal deformation caused by the seasonal water level changes of Tehri reservoir in the Garhwal region ofNWHimalaya from GPS measurements and Interferometric Synthetic Aperture Radar (InSAR) analysis. All GPS sites along the Himalaya are strongly influenced by seasonal hydrological and atmospheric loading. However, the GPS siteKUNRlocated near the reservoir additionally exhibits anomalous variations due to seasonal water loading and unloading by the reservoir. Our InSAR analysis confirms that the seasonal filling of the reservoir causes measurable subsidence in its neighbourhood. In addition to the elastic deformation caused by the seasonal reservoir loading and the negligible poroelastic deformation caused by associated fluid pressure changes, there is an unaccounted biannual deformation in the east component of the GPS time-series which we suspect to be caused by altered hydrological conditions due to the reservoir operations. Understanding crustal deformation processes due to such anthropogenic sources helps in separating deformation caused by tectonic, hydrological and atmospheric effects from that caused by these activities.

Low deformation rate in the Koyna–Warna region, a reservoir triggered earthquake site in west-central stable India

We analyse nine years of GPS measurements of crustal deformation from the Koyna–Warna region within the stable India plate. The Koyna–Warna region experienced a strong earthquake on 10 December 1967 (M 6.3) that is considered to have been induced by the impoundment of the Koyna reservoir and the continuing earthquake activity in the region is considered to be associated with the Koyna and Warna reservoirs. The earthquakes occur in a very small region of 30×10km2 in two well defined seismic zones, the NNE–SSW trending Koyna Seismic zone, and the NNW–SSE trending Warna Seismic Zone. These zones are characterised by predominantly left-lateral strike slip motion and normal motion, respectively. In 2003, we initiated campaign-mode GPS measurements in the region. Analysis of the GPS data collected over nine years indicate low to moderate deformation rate (<2±0.5mm/year) at a few sites within and close to the fault zones and no resolvable deformation elsewhere. This has been seen in many intra-plate seismic regions of the world with varying causative mechanism for the deformation. In the Koyna Warna region, the observed surface displacement rates of up to 2mm/year near the fault zones are consistent with a fault slip rate of about 7mm/year, and with the inferred sense of motion on the faults. The inferred fault slip rate is consistent with the total moment release during earthquakes of past six years in the Koyna Warna region which may imply that the ongoing earthquake activity causes the deformation in the region.

Oblique convergence and slip partitioning in the NW Himalaya: Implications from GPS measurements

We report GPS measurements of crustal deformation across the Kashmir Himalaya. We combined these results with the published results of GPS measurements from the Karakoram fault system and suggest that in the Kashmir Himalaya, the motion between the southern Tibet and India plate is oblique with respect to the structural trend. We estimated this almost north-south oblique motion to be 17 ± 2 mm/yr, which is partitioned between dextral motion of 5 ± 2 mm/yr on the Karakoram fault system and oblique motion of 13.6 ± 1 mm/yr with an azimuth of N198°E in the northwest-southeast trending Kashmir Himalayan frontal arc. Thus, the partitioning of the India-Southern Tibet oblique motion is partial in the Kashmir Himalayan frontal arc. However, in the neighboring Nepal Himalaya, there is no partitioning; the entire India-Southern Tibet motion of 19–20 mm/yr is arc normal and is accommodated entirely in the Himalayan frontal arc. The convergence rate in the Kashmir frontal Himalaya is about 25% less than that in the Nepal Himalayan region. However, here the Karakoram fault system accommodates about 20% of the southern Tibet and Indian plate convergence and marks the northern extent of the NW Himalayan arc sliver. The Kaurik Chango rift, a north-south oriented seismically active cross-wedge transtensional fault appears to divide the sliver in two parts causing varying translatory motion on the Karakoram fault on either side of the Kaurik Chango rift.

Nine years of GPS measurements of crustal deformation at Imphal, Indo-Burmese wedge

We report results of 9 years of GPS measurements of crustal deformation at Imphal, Manipur, a site located in the Indo-Burmese wedge of northwest Sunda arc. The analysis of these measurements suggests that the site moves at a rate of about 36.3±0.5 mm/year towards N55° in the ITRF2008. With respect to the Indian plate it moves at a rate of 16.7 mm/year towards N222°, i.e., predominantly towards southwest. The site is located about 15 km east of the Churachandpur Mao fault (CMF), which is reported to accommodate part of the India-Sunda motion. The site motion is not significantly affected by the earthquakes that occurred in the nearby region. However, the 2004 Sumatra-Andaman earthquake caused a coseismic displacement of ∼ 3–5 mm predominantly towards southwest. The site motion is almost linear, with some seasonal variation, and does not show any evidence of accelerated slip or slow earthquake on the CMF or along the plate boundary.

Aseismic plate boundary in the Indo-Burmese wedge, northwest Sunda Arc

Plate motion, crustal deformation, and earthquake occurrence processes in the northwest Sunda Arc, which includes the Indo-Burmese wedge (IBW) in the forearc and the Sagaing fault in the backarc, are very poorly constrained. Plate reconstruction models and geological structures in the region suggest that subduction in the IBW occurred in the geological past, but whether it is still active and how the plate motion between the India and Sunda plates is partitioned between motion in the IBW and Sagaing fault is largely unknown. Recent GPS measurements of crustal deformation and available long-term rates of motion across the Sagaing fault suggest that ∼20 ± 3 mm/yr of the relative plate motion of ∼36 mm/yr between the India and Sunda plates is accommodated at the Sagaing fault through dextral strike-slip motion. We report results from a dense GPS network in the IBW that has operated since 2004. Our analysis of these measurements and the seismicity of the IBW suggest that the steeply dipping Churachandpur-Mao fault in the IBW accommodates the remaining motion of ∼18 ± 2 mm/yr between the India and Sunda plates through dextral strike-slip motion, and this motion occurs predominantly through velocity strengthening frictional behavior, i.e., aseismic slip. The aseismic motion on this plate boundary fault significantly lowers the seismic hazard due to major and great interplate earthquakes along this plate boundary.

Localized crustal deformation in the Godavari failed rift, India

Six years of GPS measurements of crustal deformation in the Godavari failed rift (GFR) of stable India plate suggest very localized deformation. Elsewhere, all along the GFR the deformation is very low (<1.5mm/yr). Localized deformation (up to 3.3±0.5mm/yr) at least at two sites, implying compression on steep faults located on the southern margin of the GFR, is coincident with the region characterized by high level low-magnitude seismicity of past six years and implies strain accumulation for future moderate to strong magnitude earthquake in the region. The localized deformation is consistent with the view about deformation in such regions where seismicity migrates and deformation rate changes with time.

Could a megaquake occur in the Himalayas?

GPS measurements of crustal deformation are showing that a magnitude 9 earthquake could occur in the Himalayas. Roger Bilham of the University of Colorado at Boulder reported at the AGU Fall Meeting that the region, known to be seismically active, could produce a much larger earthquake than previously thought. Bilham and colleagues used GPS to monitor rates of crustal deformation in the Himalayas. They found that the potential rupture zone is larger than scientists had believed—the region where strain is building is twice as wide as expected. Previous estimates, which were based on the historical earthquake record, suggested that the largest earthquake that would occur in the region would have a magnitude in the low 8s. Such an earthquake could be devastating—the Kashmir valley region alone is home to 6 million people.

Crustal deformation measurements in Guerrero, Mexico

GPS measurements of crustal deformation in Guerrero, southern Mexico, include surveys collected between 1992 and 2001 as well as continuous GPS measurements at a few sites. These geodetic observations are used to calculate interseismic deformation rates and assess the presence and possible location of transient deformation during the period encompassing 1992.25 to 2001.75. The data are used to examine transient deformation in 1998 previously described from data at a single site by Lowry et al. [2001]. Survey measurements and continuous data from a site near Popocatépetl volcano confirm the 1998 transient, and survey data also suggest another transient occurred following the 14 September 1995 (Mw = 7.3) Copala earthquake. All of the available GPS position estimates have been inverted for a combined model of slip during each event plus the steady state slip on the plate interface. Modeling of the steady state deformation rates confirms that the Guerrero seismic gap is partially frictionally locked at depths shallower than about 25 km and accumulating strain that may eventually be released in a great earthquake. The data also suggest that there is frictional coupling to much greater (&gt;40 km) depths, which releases more frequently in aseismic slip events. The locations and sizes of the transient events are only partially constrained by the available data. However, the transient models which best fit the GPS coordinate time series suggest that aseismic slip was centered downdip of the seismogenic portion of the plate‐bounding thrust in both events, and the moment release had equivalent magnitudes Mw = 7.1 + 1.3/−1.0 in 1995–1996 and 7.1 + 0.4/−0.1 in 1998.

GPS measurements of crustal deformation in the Baikal‐Mongolia area (1994–2002): Implications for current kinematics of Asia

We present new geodetic results of crustal velocities over a large part of northern Asia based on GPS measurements in the Baikal rift zone and Mongolia spanning the 1994–2002 period. We combine our results with the GPS velocity field for China of Wang et al. [2001] and derive a consistent velocity field for most of Asia. We find contrasted kinematic and strain regimes in Mongolia, with northward velocities and N‐S shortening in westernmost Mongolia but eastward to southeastward motion and left‐lateral shear for central and eastern Mongolia. This eastward to southeastward motion of central and eastern Mongolia is accommodated by left‐lateral slip on the E‐W trending Tunka, Bolnay, and Gobi Altay faults (2 ± 1.2 mm yr−1, 2.6 ± 1.0 mm yr−1, and 1.2 mm yr−1, respectively) and by about 4 mm yr−1 of extension across the Baikal rift zone. Consequently, ∼15% of the India‐Eurasia convergence is accommodated north of the Tien Shan, by N‐S shortening combined with dextral shear in the Mongolian Altay and by eastward displacements along major left‐lateral strike‐slip faults in central and eastern Mongolia. We find a counterclockwise rotation of north and south China as a quasi‐rigid block around a pole north of the Stanovoy belt, which rules out the existence of an Amurian plate as previously defined and implies &lt;2 mm yr−1 of left‐lateral slip on the Qinling Shan fault zone.