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The results of recent stress measurements along the San Andreas fault near Palmdale, California, which show a rapid decrease in shear stress in the proximity of the fault, may be due to the stress drop connected with the great 1857 earthquake, superimposed onto a preseismic ground deformation. This suggestion is made on the basis of a fault model where a preseismic phase of stable sliding at depth is responsible, through stress concentration, for the occurrence of seismic ruptures in the upper lithosphere.

Although forecasting an occurrence of phreatic eruption is very difficult, it has been reported that some precursory activities often precede these eruptions at several volcanoes. In this study, we observed seismic activities before and during the 2008 phreatic eruption at Meakan-dake volcano, eastern Hokkaido, Japan, by using broadband seismometers and surface mount-type tiltmeters. The precursory increase in seismicity began in late September about 2 months before the first eruption on November 18. After several rises and falls in seismicity in October and in early November, a small volcanic tremor was observed early on November 16. Although the original velocity seismogram of the tremor generally appeared to be spindle shaped, an outstanding ramp function appeared in the displacement seismogram obtained by simple integration. Since the ramp function appeared only in the horizontal components and continued for about 3 min, which is sufficiently longer than the natural period of the seismometer, we regarded the ramp function as an expression of the tilting motions of seismic stations that was quantitatively confirmed by the strong similarity between horizontal displacement seismograms and tilt data from co-located biaxial tiltmeter. Azimuthal distribution of three tilting vectors obtained from broadband seismograms was not consistent with a simple spherical source but rather strongly suggested a vertical dike under the crater. In this study, we confirmed that an almost vertical single dike effectively explains the observed tilting vectors. The estimated volume increase in the dike was 4-5 x 10(4) m(3). The strike direction of the dike is highly consistent with the alignment of the hydrothermal area on and around the volcano. Our dike model also partially explains the changes in global navigation satellite system (GNSS) measurement and in groundwater levels reported in previous research. Since a similar deformation coincided with a volcanic tremor preceding the 2006 eruption, we interpret that this must be an important preparatory process of phreatic eruptions at Meakan-dake volcano.

This paper analyses the ground deformations occurring on the eastern part of the Pernicana Fault from 1997 to 2005. This segment of the fault was monitored with three local networks based on GPS and EDM techniques. More than seventy GPS and EDM surveys were carried out during the considered period, in order to achieve a higher temporal detail of ground deformation affecting the structure. We report the comparisons among GPS and EDM surveys in terms of absolute horizontal displacements of each GPS benchmark and in terms of strain parameters for each GPS and EDM network. Ground deformation measurements detected a continuous left-lateral movement of the Pernicana Fault. We conclude that, on the easternmost part of the Pernicana Fault, where it branches out into two segments, the deformation is transferred entirely SE-wards by a splay fault.

We present ground deformation maps for the southern Saskatchewan region between Rice Lake and the City of Saskatoon measured by Radarsat-2 Differential Interferometric Synthetic Aperture Radar (DInSAR) during 2008–2011. We acquired and processed Radarsat-2 data from two different tracks (Multi-Look Fine beam and one Standard beam) and performed advanced interferometric analysis that revealed ground deformation with a maximum line-of-sight rate close to 10 cm per year. Decomposition of ascending and descending, line-of-sight images into horizontal (mainly east–west) and vertical components revealed the presence of localized horizontal motion with a maximum absolute rate of 4 cm per year and subsidence with a maximum rate of −10 cm per year. These results suggested that simple line-of-sight time series analysis of interferometric data acquired in single geometry is insufficient for capturing a complete pattern of ground deformation and can be misleading in the presence of both horizontal and vertical components of deformation., KFT and PJG are supported by an NSERC Discovery Grant.

We present observations of ground deformation at Sakurajima in August 2015 and model the deformation using a combination of GNSS, tilt and strain data in order to interpret a rapid deformation event on August 15, 2015. The pattern of horizontal displacement during the period from August 14 to 16, 2015, shows a WNW–ESE extension, which suggests the opening of a dike. Using a genetic algorithm, we obtained the position, dip, strike length, width and opening of a dislocation source based on the combined data. A nearly vertical dike with a NNE–SSW strike was found at a depth of 1.0 km below sea level beneath the Showa crater. The length and width are 2.3 and 0.6 km, respectively, and a dike opening of 1.97 m yields a volume increase of 2.7 × 106 m3. 887 volcano-tectonic (VT) earthquakes beside the dike suggest that the rapid opening of the dike caused an accumulation of strain in the surrounding rocks, and the VT earthquakes were generated to release this strain. Half of the total amount of deformation was concentrated between 10:27 and 11:54 on August 15. It is estimated that the magma intrusion rate was 1 × 106 m3/h during this period. This is 200 times larger than the magma intrusion rate prior to one of the biggest eruptions at the summit crater of Minami-dake on July 24, 2012, and 2200 times larger than the average magma intrusion rate during the period from October 2011 to March 2012. The previous Mogi-type ground deformation is considered to be a process of magma accumulation in preexisting spherical reservoirs. Conversely, the August 2015 event was a dike intrusion and occurred in a different location to the preexisting reservoirs. The direction of the opening of the dike coincides with the T-axes and direction of faults creating a graben structure.

Ground deformation has been demonstrated to be one of the most common signals of volcanic unrest. A variety of processes can cause ground deformation in active volcanic areas (e.g. magmatic processes, pore pressure variations in the hydrothermal systems, etc), and being able to recognize and distinguish them is crucial for evaluating the potential occurrence of future eruptions. Ground deformation can be measured using remote sensing or geodetic techniques like GPS or tiltmeters. However, even if geodetic monitoring networks may be capable of recording the ground deformation signal at surface, it is difficult to directly identify where and how are the pressure sources responsible for the observed deformation. Deception Island is the most active volcano in the South Shetland Islands, which last destructive events took place in 1967, 169 and 1970. Since the installation of the monitoring network in the island, it has experienced three uplift/downlift episodes, where ground deformation has been measured with GPS stations. . The objective of this work is to evaluate the location, shape, pressure source responsible for surface ground deformation recorded in Deception Island during the period 1995 - 2000 using Finite Elements (FE) linear elastic models. First, we have considered a 2D model where we have studied the effect of the different parameters in ground deformation. Second, 3D models simulating the real topography of Deception Island have been considered. The results of the 3D models are compared with the GPS data registered in some points of the island to approximate the shape, depth, excess pressure of the reservoir. Results obtained are crucial to understand the current magmatic situation of the island and the potential outcome of a future eruption.

This paper presents the application of Differential Synthetic Aperture Radar (SAR) interferometry (DInSAR) algorithms for the precise monitoring of earth dams ground deformation. The test site selected for this study is the Conza Dam, located in the southern Apennines (Italy), very close to the epicenter of the big earthquake (M-w = 6.9) which took place on November 23th, 1980, striking the Irpinia region. Among the multiple advanced DInSAR techniques developed by the SAR community during the last decade, this work uses the so-called SUBSOFT software, developed by the Remote Sensing Laboratory (RSLab) group from the Universitat Politecnica de Catalunya (UPC), which is based on the use of Coherent Pixels Technique (CPT) algorithm. The analysis is carried out using 51 ENVIronmental SATellite-Advanced Synthetic Aperture Radar (ENVISAT-ASAR) images, corresponding to the period from 29th of November 2002 to the 30th of July 2010. In this framework, ground displacements recorded by a network of conventional ground-based sensors are also available for the same temporal span. Indeed, the embankment dam is well instrumented to measure internal settlements by means of cross-arms placed in six different cross-sections, and superficial displacements by means of targets for precise leveling. A statistical analysis has been performed to carry out a better comparison between the measurements obtained with the conventional field sensors and the interferometric data. The high agreement between final DInSAR displacements and in-situ instrumental data, demonstrates the reliability of such technique for the precise monitoring of civil infrastructures, and concretely, in dams with a high exposure factor and its consequent risk.

A sequence of two strike-slip earthquakes occurred on April 14 and 16, 2016 in the intraplate region of Kyushu Island, Japan, apart from subduction zones, and caused significant damage and disruption to the Kumamoto region. The analyses of regional seismic catalog and available strong motion recordings reveal striking characteristics of the events, such as migrating seismicity, earthquake surface rupture, and major foreshock-mainshock earthquake sequences. To gain valuable lessons from the events, a UK Earthquake Engineering Field Investigation Team (EEFIT) was dispatched to Kumamoto, and earthquake damage surveys were conducted to relate observed earthquake characteristics to building and infrastructure damage caused by the earthquakes. The lessons learnt from the reconnaissance mission have important implications on current seismic design practice regarding the required seismic resistance of structures under multiple shocks and the seismic design of infrastructure subject to large ground deformation. The observations also highlight the consequences of cascading geological hazards on community resilience. To share the gathered damage data widely, geo-tagged photos are organized using Google Earth and the kmz file is made publicly available.

Radar Interferometry is a widely used method for estimating ground deformation, as it provides precision to a few millimeters to centimeters, and at the same time, a wide spatial coverage of the study area. On 9 July 1956, one of the strongest earthquakes of the 20th century in the area of the South Aegean, occurred in Amorgos, with a magnitude of Mw = 7.7. The objective of this research is to map ground deformation in Amorgos island, using InSAR techniques. We conducted a multi-temporal analysis of all available data from 2003 to 2019 by exploiting historical ENVISAT SAR imagery, as well as the dense archive of Sentinel-1 SLC imagery. Persistent Scatterer Interferometry (PS) and Small Baseline Subset (SBAS) methods were implemented. Results of both data-sets indicate a small-scale deformation on the island. A multi-track analysis was implemented on Sentinel-1 data to decompose the line of sight velocities to vertical and horizontal. The central south coast is experiencing horizontal movement, while uplift of a maximum value of 5 mm/y is observed in the southeastern coast. The combination of the good spatial coverage achievable via InSAR, with GPS measurements, is suggested an important tool for the seamless monitoring of Amorgos island towards tectonic hazard estimation.