Observation Of Crustal Deformation Research Articles

Glacial rebound and plate spreading: results from the first countrywide GPS observations in Iceland

Iceland is one of the few places on Earth where a divergent plate boundary can be observed on land. Direct observations of crustal deformation for the whole country are available for the first t ...

Evaluation of Detection Level of Crustal Deformation Observation in the Time Domain through Power Spectrum Analysis

Evaluation of Detection Level of Crustal Deformation Observation in the Time Domain through Power Spectrum Analysis

Continuous Observation of Crustal Deformation in Tohoku University

Continuous Observation of Crustal Deformation in Tohoku University

Detectability for GPS, EDM and tiltmeters of the Hot Springs Research Institute in the western Kanagawa prefecture, Japan

To better understanding the observation data, we attempt to assess the detectability for the crustal deformation observation network of the Hot Springs Research Institute of Kanagawa prefecture (HSRI). The HSRI has carried out continuous monitoring of crustal deformation with GPS, EDM, borehole tiltmeters, groundwater leveling since 1989. Our observation purpose is to detect the pre-, co- and post-seismic deformations of the hypothetical M7 class earthquake designated as the “Western Kanagawa Prefecture Earthquake (WKE)”. In order to estimate the detectability, weapplya simple calculation method, thatiscomparing between co-seismic deformation (displacement and tilt) and the accuracy of observation instruments. Co-seismic deformation is calculated using the Okada’s method, which is a formulation of the expected crustal deformation due to seismic faulting as a function of an earthquake magnitude and a hypocentral distance without assuming focal mechanism. It is indicated that the highest detectability area is located in the center of our HSRI observation network. Comparing detectability contour maps for several kinds of networks, we can find that the detectability of the co-seismic deformation by the tiltmeter network is higher than those by the GPS and EDM networks in the case of the M5 class earthquake with a focal depth of 10 km, and that the detectability by the GPS network is almost equal to that by the EDM network in the case of the M6 class earthquake with a focal depth of shallower than 15 km. For M4 class earthquakes, it is difficult for the GPS, EDM and tiltmeter networks to detect co-seismic deformation. The present result shows advantageous characteristics of the HSRI geodetic network and an important constraint on investigating the pre-, co- and post-seismic deformation of the WKE. To monitor the pre-, co- and post-seismic deformation of the WKE, it is necessary to combine these observations in the most effective way.

Postglacial rebound at the northern Cascadia subduction zone

Postglacial rebound is the response of the Earth to the decay of ice-sheets. A postglacial rebound model explains crustal tilting and rapid uplift at the northern Cascadia subduction zone that occurred during retreat of the Cordilleran ice-sheet. Observations explained by the model include the shoreline tilts of two proglacial lakes that formed at 13.5–14 ka ( 14 C yr ago) and rapid sea level fall (land uplift) at 12–12.5 ka. Modelled mantle viscosity values range from 5×10 18 to 5×10 19 Pa s, and are consistent with previous viscosity inferences from observations of crustal deformation following subduction zone earthquakes (10 18–10 19 Pa s). No lower limit to subduction zone mantle viscosity is apparent from our model, but viscosity values equal to or larger than 10 20 Pa s are definitely ruled out. Our modelled subduction zone viscosity values are smaller than most upper-mantle viscosity estimates derived from postglacial rebound studies of tectonically less-active regions (10 20–10 21 Pa s). The rapid observed uplift at 12 ka requires, in addition to a low mantle viscosity, rapid unloading from a sudden collapse of remaining coastal portions of the southern Cordilleran ice-sheet. The sudden collapse provides 0.18 m of global eustatic sea level rise, approximately 0.7% of the sea level rise associated with melt-water pulse IA. Predictions of a global postglacial rebound model (ICE-3G) with a 10 21 Pa s upper-mantle viscosity were previously applied to geodetic data from this region to isolate signals associated with the earthquake cycle. Owing to the low-viscosity values, and resulting rapid recovery of glacial deformation, our model predicts present-day postglacial rebound uplift rates at least 10 times smaller than ICE-3G (less than about 0.1 mm/yr). As the ICE-3G adjustments were substantial, this indicates the need for re-evaluation of the geodetic data.

A model for possible crustal deformation prior to a coming large interplate earthquake in the Tokai district, central Japan

Abstract We perform numerical simulations of a seismic cycle by applying a laboratory-derived friction law to evaluate possible crustal deformations prior to the hypothesized Tokai earthquake, which is expected to occur in the near future along the Suruga trough, central Japan. The frictional force obeying a rate- and state-dependent friction law is assumed to act on the plate interface in a 2D model of the subduction zone. We test two versions of the friction law: the so-called slowness version and the slip version. We select model parameters on the basis of historical documents about past large earthquakes in the Tokai district and the present coupling state of the plate interface beneath the Tokai district estimated by GPS observations. Simulation results for both the slowness and the slip version are as follows: (1) The coupling region of the plate interface becomes narrower with time in the interseismic period. (2) The inland crust contracts at a nearly constant rate for most of the interseismic period. The contraction rate decreases or a change from contraction to extension takes place before the occurrence of a large interplate earthquake. (3) Significant abnormal crustal deformation precedes the earthquake, and maximum amplitudes about one day before the earthquake exceed the noise levels in the case of clear weather of borehole strainmeters installed in the Tokai district. (4) The spatiotemporal variation of aseismic sliding on the plate interface perturbs the regional stress field around the source volume of the coming earthquake, leading possibly to precursory seismic quiescence in the overriding plate and a change in focal mechanisms of small earthquakes in the subducting slab. The most significant difference in the results between the slowness version and the slip version of the friction law is that amplitudes of preslip and crustal deformation just before earthquakes are several times larger for the slowness version than for the slip version. Although some ambiguity remains in the present model mainly because of the incompleteness of the friction law and the deficiency of observational data constraining model parameters, the physical model can be improved through the comparison of predicted crustal deformation with observations. Continuous and concentrated observations of crustal deformation and seismic activity are thus important in the Tokai district to understand quantitatively the sliding process preceding a large interplate earthquake there.

P58 三宅島の地震・地殻変動観測

P58 三宅島の地震・地殻変動観測

Crustal deformation in the mid-May 1991 crisis preceding the extrusion of a dacite lava dome at Unzen volcano, Japan

Tilt observations at FG1 station located about 680 m west of the central crater of Unzen volcano, southwestern Japan, revealed details about the process of magma ascent during the mid-May 1991 crisis, just before the appearance of a lava dome. Crustal deformations measured during this period can be interpreted by a combination of upward growth of a buried magma column and lateral intrusion of a dike, modeled by a vertical line source and a planer tensile dislocation in an elastic half space. Marked change in tilt was observed at first in the EW direction at FG1 during May 11–14, suggesting the ascent of a magma column with a diameter of about 40 m from about 300 m to 160 m in depth beneath the central crater. After the interruption of the rise of the magma column, magma began to intrude laterally as a dike on May 15 toward approximately the N80°W direction. This resulted in a large tilt change essentially in the NS component at FG1. The horizontal extent of the dike might have exceeded 400 m in a few days with a thickness of about 6 m. On May 17, the magma column started to rise again, probably because the impediment to magma ascent was fractured by the growth of the dike. The top of the magma column finally reached to the crater bottom probably on May 19, and a new lava dome was actually observed on May 20. After which, the remarkable upward tilt to the south at FG1 due to the dike intrusion decreased rapidly. The deformation after May 20 can be interpreted by a gradual increase in the thickness of the dike up to 13 m by the end of May 1991. Although large errors are inevitable in estimated values because of a lack of sufficient data, the present results confirm the importance of making continuous observations of crustal deformation near the summit areas of active volcanoes in order to clarify the underground processes of magma movement leading to eruptions.

GPS observation of crustal deformation in the Taiwan‐Luzon Region

Fifteen GPS stations in the Batan‐Luzon area were surveyed three times during 1996 to 1998. In order to study crustal deformation in the Taiwan‐Luzon region, the data from these annual surveys are processed together with data from 20 permanent stations in the Taiwan area and IGS stations in the Asia‐Pacific region. We found that the Chinese continental margin is moving in directions of 102°–112° with rates of 11–12 mm/yr relative to stable Eurasia. There is a significant southward increase in crustal motion with respect to Eurasia along the N‐S trend of the Luzon arc. In the Coastal Range of Taiwan, the velocity is 53 mm/yr in the direction 313°. Further south at two volcanic islands, Lanhsu and Batan, the velocities increase to 68 mm/yr in the direction 306° and 81 mm/yr in the direction 299°, respectively. In northern Luzon the velocity reaches 86 mm/yr in the direction 301°. Remarkable fault slips of 17–31 mm/yr across the Philippine fault system are detected.

プレート境界面で発生する余効すべりの数値シミュレイション

A numerical study is performed to investigate the physical process of postseismic sliding on a plate boundary in a subduction zone. Sliding process of a plate boundary in a 2-D uniform elastic half-space is numerically computed on the assumption that the frictional force obeys a rate- and state-dependent friction law. Postseismic sliding takes place especially at the slip-rate-strengthening regions that are shallower or deeper than the seismogenic zone. The temporal variation of cumulative moment release is well approximated by a logarithmic function. The characteristics of simulated postseismic sliding are consistent with the sliding processes following Off Sanriku earthquakes estimated from the observation of crustal deformation. The comparison of the modeling on the basis of the friction law for postseismic sliding with the observed data of crustal deformation is important not only for understanding the subduction process in the earth but also for estimating friction parameters on the plate boundary.

Quantitative Prediction of volcanic Eruption by Crustal Deformation Observation

Quantitative Prediction of volcanic Eruption by Crustal Deformation Observation

Possibility for Observation of Crustal Deformation by means of Dense GPS Network

Possibility for Observation of Crustal Deformation by means of Dense GPS Network

Behavior of the brittle crust in wide plate boundary zones

In wide and active continental plate boundary zones, ductile flow in the deeper and strong parts of the lithosphere may control crustal deformation. This is likely if average resistive shear stresses on faults in the brittle crust are much less than 108 Pa and the underlying bulk effective viscosity is much greater than 1021 Pa s. In this case, a simple model of distributed deformation, referred to as the floating block model, may be useful. This treats the crust as an array of rotating and translating rigid blocks, which are floating on an underlying continuous flow with a constant rheology. The model is analyzed in detail in this paper because it has the potential to link detailed observations of crustal deformation with the large‐scale flow. Crustal blocks are defined by at least two sets of faults. The kinematics of crustal deformation can be described in terms of the motions of these blocks. Both the relative motion on block boundaries (faults) and block tilting about a horizontal axis can be described in terms of the underlying flow and block rotation about a vertical axis. However, rotations about a vertical axis, which are an important component of the crustal deformation, will depend not only on the underlying flow but also on the shape, orientation and arrangement of the crustal blocks. The average rotation rate about a vertical axis, over finite rotations, will be significantly different from that predicted at any instant. Also, the rotation history is considerably complicated if, as is likely, the underlying flow field, or block shape, has changed with time. These aspects of crustal deformation are discussed with reference to real zones of active deformation in New Zealand, Greece and western North America.

Detection of a volcanic fracture opening in Japan using Global Positioning System measurements

THE Global Positioning System (GPS) is a powerful tool for detecting crustal deformation1; for example, the technique has been used to detect plate boundary movements in California2. Here we report observations of crustal deformation associated with seismic swarm and sea-floor volcanic activity off the east coast of the Izu Peninsula, Japan, in July 1989, using a fixed-point GPS network. These measurements have enabled us to capture some rarely observed features of seismic and volcanic activity. We have, for the first time, used GPS fixed-point measurements to follow the evolution with time of the crustal movements; such measurements provide a continuous uninterrupted record of deformation. Our observations were supported by independent data from other sources, thus providing further evidence for the utility of the GPS.

Observation of Crustal Deformation in Wide Area

Observation of Crustal Deformation in Wide Area

Source parameters of the October 1, 1987 Whittier Narrows Earthquake from crustal deformation data

Offsets in the regional strain field, generated by the October 1, 1987, Whittier Narrows earthquake, were recorded with large amplitudes on two deep‐borehole dilational strainmeters at distances of 46.7 and 65.5 km from the hypocenter and marginally on instruments at greater distances in the Parkfield area and at Pinon Flat, where laser extensometers also recorded small offsets. These data are insufficient to solve for the location and physical parameters of the earthquake, but by also using the measured elevation changes in the epicentral area, we are able to invert for source models consistent with all available observations of crustal deformation. The source models obtained indicate that slip extends to a depth of about 30 km, well below the recorded aftershock zone. The requirement for deeper (and presumably aseismic) slip derives from the large negative dilatation experienced by the nearest strainmeter (PUBS), but high‐frequency data from the same site exclude any significant slow component of moment release. By ignoring PUBS we obtain a moment of about 0.7 × 1018 N m on a fault that has a strike and dip of about N60°W and 40° down to the north, respectively, and extends to a depth of about 16 km. The most likely reason for the anomalous offset at PUBS appears to be sympathetic slip triggered on a nearby fault by the main shock. Precursive strain during the month prior to the earthquake is not apparent at the nanostrain level in the data from the closest instrument, but the event was accompanied by a change in strain rate at the two nearer sites.

Continuous Observation of Crustal Deformation by Using Borehole?type Instruments

Continuous Observation of Crustal Deformation by Using Borehole?type Instruments

Observation of Crustal Deformation at the Fujigawa Observatory, Central Honshu, Japan (3)

Observation of Crustal Deformation at the Fujigawa Observatory, Central Honshu, Japan (3)

阿武山における地殻変動の連続観測(1972-1977)

阿武山における地殻変動の連続観測(1972-1977)

Observation of Crustal Deformation at the Fujigawa Observatory, Central Honshu, Japan

Observation of Crustal Deformation at the Fujigawa Observatory, Central Honshu, Japan