Years Of GPS Measurements Research Articles

Recent ground deformation around lake Nasser using GPS and InSAR, Aswan, Egypt

The rate of seismic activity around lake Nasser rapidly increased after the creation of the High Dam. The largest earthquake was of magnitude ML 5.6 ; it occurred on November 14th 1981, 60 km southwest of the Aswan High Dam. We use 16 years of GPS measurements collected around the northern part of lake Nasser, represented by 27 GPS sites, plus eight years of Envisat SAR scenes, 35 descending scenes, to estimate the recent ground movement of this area. GPS and InSAR showed a land subsidence localized around lake Nasser. The subsidence has a magnitude of 1–2 mm/yr. Therefore, we model the Earth's response to water level changes, using full daily water level variations starting from 1982 to 2016. Our loading model captures a similar deformation pattern, like ones estimated from GPS and InSAR, around the lake with comparable amplitudes. With respect to stable Nubia, most of GPS sites around the lake show a negligible North to Northeast motion of <1 mm/yr. Along Kalabsha fault, we estimate a strike-slip motion with an extension component of 0.6 mm/yr. GPS sites around Sayal fault do not show any differential motion along the fault in both fault-parallel and fault-normal components. The InSAR result would not be able to capture the deformation at Kalabsha and Sayal region, since the deformation in this area is <1 mm/yr.

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.

Nine Years of GPS Measurements of Crustal Deformation at Imphal, Indo-Burmese Wedge

Abstract 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 N55º in the ITRF2008. With respect to the Indian plate it moves at a rate of 16.7 mm/year towards N222º, 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.

Active tectonics in Quito, Ecuador, assessed by geomorphological studies, GPS data, and crustal seismicity

AbstractThe Quito Fault System (QFS) extends over 60 km along the Interandean Depression in northern Ecuador. Multidisciplinary studies support an interpretation in which two major contemporaneous fault systems affect Quaternary volcanoclastic deposits. Hanging paleovalleys and disruption of drainage networks attest to ongoing crustal deformation and uplift in this region, further confirmed by 15 years of GPS measurements and seismicity. The resulting new kinematic model emphasizes the role of the N‐S segmented, en echelon eastward migrating Quito Fault System (QFS). Northeast of this major tectonic feature, the strike‐slip Guayllabamba Fault System (GFS) aids the eastward transfer of the regional strain toward Colombia. These two tectonic fault systems are active, and the local focal mechanisms are consistent with the direction of relative GPS velocities and the regional stress tensor. Among active features, inherited N‐S direction sutures appear to play a role in confining the active deformation in the Interandean Depression. The most frontal of the Quito faults formed at the tip of a blind thrust, dipping 40°W, is most probably connected at depth to inactive suture to the west. A new GPS data set indicates active shortening rates for Quito blind thrust of up to 4 mm/yr, which decreases northward along the fold system as it connects to the strike‐slip Guayllabamba Fault System. The proximity of these structures to the densely populated Quito region highlights the need for additional tectonic studies in these regions of Ecuador to generate further hazard assessments.

Crustal deformation along the Dead Sea Transform and the Carmel Fault inferred from 12 years of GPS measurements

Large‐scale crustal deformation in the Levant is mainly related to the DST and the CFS. The former is an active left lateral transform, bounding the Arabian plate and the Sinai sub‐plate, and the latter branches out of the former and separates the Sinai sub‐plate into two tectonic domains. In this study we obtain the velocities of 33 permanent GPS stations and 145 survey stations that were surveyed in three campaigns between 1996 and 2008. We use a simple 1‐D elastic dislocation model to infer the slip rate and locking depth along various segments of the DST. We infer a 3.1–4.5 mm/yr slip rate and a 7.8–16.5 km locking depth along the DST north of the CFS, and a slip rate of 4.6–5.9 mm/yr and locking depth of 11.8–24 km along the Jericho Valley, south of the CFS. Further south, along the Arava Valley we obtain a slip rate of 4.7–5.4 mm/yr and a locking depth of 12.1–23 km. We identify an oblique motion along the Carmel Fault with ∼0.7 mm/yr left‐lateral and ∼0.6 mm/yr extension rates, resulting in N‐S extension across the Carmel Fault. This result, together with the decrease in DST slip velocity from the Jericho Valley to the segment north of the CFS, confirms previous suggestions, according to which part of the slip between Arabia and Sinai is being transferred from the DST to the CFS.

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.

Determining and modeling tectonic movements along the central part of the North Anatolian Fault (Turkey) using geodetic measurements

The North Anatolian Fault (NAF), which extends from Karlıova in Eastern Turkey to the Gulf of Saros in the Northern Aegean Sea, is one of the longest active strike-slip faults in the world with a length of about 1500 km. Within the North Anatolian Shear Zone (NASZ) there are long splays off the main trunk of the NAF veering towards the interior parts of Anatolia. Although the whole shear zone is still seismically active, the major seismicity is concentrated along the main branch of the NAF. Splays of the NAF dissect the shear zone into different continental blocks. The largest splay of the NAF was selected to analyze the distribution of movements between the faults delimiting these blocks. Four years of GPS measurements and modeling results indicate that the differential motion between the Anatolian collage and the Eurasian plate along the central part of the NAF is partitioned between fault splays and varies between 18.7 ± 1.6 and 21.5 ± 2.1 mm/yr with the main branch taking ∼90% of the motion.

Estimation of subsidence using GPS measurements, and related hazard: the Pingtung Plain, southwestern Taiwan

Four years of GPS measurements were done since 1996 in southwestern Taiwan in order to investigate crustal deformation and land subsidence. The network of 48 stations revealed the velocity field in the Pingtung Plain. Horizontal velocities range from 31 to 54 mm yr −1 towards azimuths 247 ◦ to 273 ◦ . They show clear anti-clockwise deviation in the coastal area, consistent with tectonic transtension related to lateral escape at the transition collision–subduction. The deformation resembles a particle flow towards a free boundary, and is not a rigid rotation. Vertical velocities range from +13 to −25 mm yr −1 . Twenty stations show fast subsidence in the coastal area, with rates averaging −16 mm/yr. The comparison with Holocene subsidence suggests that about 75% of the present-day subsidence result from decreasing groundwater level induced by over-pumping, adding significant short-term component to the natural risk resulting from long-term tectonic subsidence. To cite this article: C.-S. Hou et al., C. R. Geoscience 337 (2005).

Monitoring of the Palu‐Koro Fault (Sulawesi) by GPS

5 years of GPS measurements across the Palu‐Koro fault (Sulawesi, Indonesia) state left lateral strike‐slip (3.4 cm/yr) with a small normal component (0.4 cm/yr). The measurements on intermediate points of the transect show that the fault is locked, at a depth estimated around 8–16 km by a very simple model. The best measured baseline linking the two most separate sites (Watatu and Toboli) shows very interestingly a constant rate of 2.6 cm/yr from 1992 to 1995, and an increased rate of 6.3 cm/yr since then. This increase is due to an earthquake on January 1, 1996 in the Minahasa trench, presumably affecting station Toboli's position by 2 cm of co‐seismic and 2 cm of post‐seismic displacement, which is added to its long term velocity. We interpret this phenomenon as additional stress loading on the Palu fault, driven by the slip during the earthquake 100 km to the North‐East.