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As one of the most sensitive instruments for deformation monitoring in geophysics, borehole strainmeter has the capability to record a large spectrum of tectonic and environmental signals. Sensors are usually deployed near active faults and volcanoes and provide high-resolution continuous recordings of seismic and aseismic signals, hydrological variations (rainfall, groundwater level) and natural hazards (tropical cyclones, landslides, tsunamis). On the occasion of the 50th anniversary of the installation of the first Sacks–Evertson borehole strainmeter, in central Japan, we present an overview of the major scientific contributions and advances enabled by borehole strainmeter measurements in Taiwan since their installation in the mid 2000s. We also propose a set of future research directions that address recent challenges in seismology, hydrology and crustal strain modeling.

YRY-4 borehole strainmeters have been installed in Sichuan Province, China, since 2008, aimed at monitoring the crustal activities associated with earthquakes. In this study, data from six YRY-4 strainmeters at the southwestern endpoint of the Longmenshan fault zone were analysed, to study the relationship of tectonic strain changes with the 2013 Lushan earthquake. We developed a state-space model to remove the strain response due to air pressure, solid tides and the changes in the water level to preferentially isolate non-tectonic disturbances. Strain responses to each influencing factor were estimated using the environmental coefficients computed in the state-space model by an adaptive Kalman filter with measurement noise. The results were consistent with the expected response of the strainmeter systems. The corrected strain considered to originate from underground tectonics provides new insights into the changes in the pre-earthquake strain. Approximate negentropy (ApNe) and ${b}$ value were introduced to quantify the probability distribution of the corrected borehole strain and compared with the local seismic activities. The nearest station and two further stations, almost simultaneously recorded short-term ApNe anomalies six to four months before the earthquake. The anomalous region also had a correspondingly low ${b}$ value. Moreover, the anomaly acceleration rates of each station were dependent on the epicentral distances. Further comparison with the strain of random periods illustrated the significance of the extracted anomalies. Our results indicate that the corrected strain may contain seismogenic information and reflect the accelerated strain accumulation of focal areas before the earthquake.

The comparison of tiltmeter and strainmeter data in the periods of the strongest earthquakes with tropical cyclone activities in the World Ocean during January–April 2014 is made. Main features of the observed co-seismic tilt and strain processes are consistent with the results obtained for the strongest events during 1997–2004. The time-frequency data analysis and the comparison of the analysis results with the anomalous geomagnetic and ionospheric activity come to an agreement with the observed phenomena. The obtained results have allowed the triggering mechanism of seismicity to be proposed. The process begins as spatial and temporal swings of the regions of tropical cyclone origins and the basins of their activity. The powerful cyclone development accompanies a wide range of earthquake precursory phenomena, including abnormal behavior of ultra-wideband (0.002 mHz–3 Hz) Earth's oscillations, which can be recorded at far distances up to 1000–10,000 km. The daily dissipation energy of the most powerful tropical cyclone (hurricane, typhoon) is estimated to have same order of magnitude as the energy released by an event of Mw 7–9, as well, atmospheric depressions are big enough to trigger a forthcoming strong earthquake. The triggering mechanism could be caused by quasi-static and time-dependent surface loading that produces vertical tension and shear deformations. This loading affects the seafloor and coastline where they fall close to the adjacent tectonic plate boundaries.

Basing on the analysis of data on variations of deformations in the Earth’s crust, which were obtained with a laser strainmeter, we found that deformation anomalies (deformation jumps) occurred at the time of tsunami generation. Deformation jumps recorded by the laser strainmeter were apparently caused by bottom displacements, leading to tsunami formation. According to the data for the many recorded tsunamigenic earthquakes, we calculated the damping ratios of the identified deformation anomalies for three regions of the planet. We proved the obtained experimental results by applying the sine-Gordon equation, the one-kink and two-kink solutions of which allowed us to describe the observed deformation anomalies. We also formulated the direction of a theoretical deformation jump occurrence—a kink (bore)—during an underwater landslide causing a tsunami.

On 13 December 2020, Etna volcano entered a new eruptive phase, giving rise to a numberof paroxysmal episodes involving increased Strombolian activity from the summit craters, lavafountains feeding several-km high eruptive columns and ash plumes, as well as lava flows. As of 2August 2021, 57 such episodes have occurred in 2021, all of them from the New Southeast Crater(NSEC). Each paroxysmal episode lasted a few hours and was sometimes preceded (but more oftenfollowed) by lava flow output from the crater rim lasting a few hours. In this paper, we use remotesensing data from the ground and satellite, integrated with ground deformation data recorded bya high precision borehole strainmeter to characterize the 12 March 2021 eruptive episode, whichwas one of the most powerful (and best recorded) among that occurred since 13 December 2020.We describe the formation and growth of the lava fountains, and the way they feed the eruptivecolumn and the ash plume, using data gathered from the INGV visible and thermal camera monitoringnetwork, compared with satellite images. We show the growth of the lava flow field associatedwith the explosive phase obtained from a fixed thermal monitoring camera. We estimate the eruptedvolume of pyroclasts from the heights of the lava fountains measured by the cameras, and the eruptedlava flow volume from the satellite-derived radiant heat flux. We compare all erupted volumes (pyroclastsplus lava flows) with the total erupted volume inferred from the volcano deflation recorded bythe borehole strainmeter, obtaining a total erupted volume of ~3 106 m3 of magma constrained bythe strainmeter. This volume comprises ~1.6 106 m3 of pyroclasts erupted during the lava fountainand 2.4 106 m3 of lava flow, with ~30% of the erupted pyroclasts being remobilized as rootlesslava to feed the lava flows. The episode lasted 130 min and resulted in an eruption rate of ~385 m3s􀀀1 and caused the formation of an ash plume rising from the margins of the lava fountain that roseup to 12.6 km a.s.l. in ~1 h. The maximum elevation of the ash plume was well constrained by anempirical formula that can be used for prompt hazard assessment.

The article presents the results of microseismic signals of the “voice of the sea” registration by a two-coordinate laser strainmeter during the passage of typhoons through and near the water area of the Sea of Japan. It was established that the “voice of the sea” microseisms appear and disappear almost simultaneously with primary microseisms, i.e., the powerful “voice of the sea” microseisms exist only in the presence of powerful wind waves, generated by a passing typhoon. According to the processing results of the obtained experimental data, the “voice of the sea” microseisms generation area is located in the “sea-land” transition zone, i.e., near and/or in the surf zone. Based on the data of the two-coordinate laser strainmeter, we determined the bearing of the “voice of the sea” microseisms generation area. The movement of this area coincides with the movement of the rear part of tropical cyclones.

As part of the collaborative GeoSciFramework project, we are establising a monitoring system for the Yellowstone volcanic area that integrates multiple geodetic and seismic data sets into an advanced cyber-infrastructure framework that will enable real-time streaming data analytics and machine learning and allow us to better characterize associated long- and short-term hazards. The goal is to continuously ingest both remote sensing (GNSS, DInSAR) and ground-based (seismic, thermal and gas observations, strainmeter, tiltmeter and gravity measurements) data and query and analyse them in near-real time. In this study, we focus on DInSAR data processing and the effects from using various atmospheric corrections and real-time orbits on the automated processing and results. We find that the atmospheric correction provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) is currently the most optimal for automated DInSAR processing and that the use of real-time orbits is sufficient for the early-warning application in question. We show analysis of atmospheric corrections and using real-time orbits in a test case over the Kilauea volcanic area in Hawaii. Finally, using these findings, we present results of displacement time series in the Yellowstone area between May 2018 and October 2019, which are in good agreement with GNSS data where available. These results will contribute to a baseline model that will be the basis of a future early-warning system that will be continuously updated with new DInSAR data acquisitions.

Since 2004 a research project has been developed to monitor subsurface deformation of Italian volcanoes using borehole strainmeters and long-baseline tiltmeters. Six Sacks-Evertson dilatometers were installed around Campi Flegrei caldera and Vesuvius during 2004–2005 (Scarpa et al., 2007), and in 2008 these instruments were supplemented by two arrays of 28–280 m long water-tube tiltmeters in underground tunnels. Relevant strainmeter and tiltmeter data have been collected and analysed from the instruments installed near Campi Flegrei caldera during the recent unrest episodes. In the period 2004–2005 strain, tilt and GPS data from Campi Flegrei indicate the onset of surface deformation that accompanied a low rate of vertical displacement that continued to 2006, corresponding to an increase of CO2 emission. This strain episode preceded caldera microseismic activity by a few months, as was observed also during a significant inflation episode in 1982. Other transient strain episodes occurred in October 2006, which were accompanied by a swarm of VT (Volcano-Tectonic) and LP (Long Period) events, in 2009, at the time of renewed gas emission activity at Solfatara, and again in March 2010, several minutes before a seismic swarm. The time scale of these transient strain events ranges from some hours to several days, putting tight constraints on the origin of ground uplifts at Campi Flegrei. Their location is compatible with a source inferred from long term deformation signals, located about 4 km beneath Pozzuoli. A proposed mechanism for these aseismic strain episodes is that they are associated with magma growth in reservoirs with occasional pressure relief associated with the leakage of gas.

In research into various hydrophysical and hydroacoustic wave processes, it is extremely important to know the regularities of their propagation in the sea at decreasing depths, especially in the shelf areas, and also to know the regularities of their transformation into seismoacoustic processes in the earth crust. In the course of the processing and analysis of the experimental data of our complex experiment, in this paper we investigate these regularities. In our experiment, we used a low-frequency hydroacoustic transmitter that generated harmonic oscillations at the frequency of 22 Hz and received hydroacoustic systems with a shore laser strainmeter. It was established that hydroacoustic waves, propagating at the shelf of decreasing depth, transform into seismoacoustic waves at the depth of the sea equal to or less than a half-length of the hydroacoustic wave. A comparison of the results of this work with earlier-obtained results allows us to state that such regularities should be inherent to all hydrophysical and hydroacoustic processes.

The results of experimental studies with a laser strainmeter and a multichannel automated geoacoustic rock pressure control system “PROGNOZ ADS” aimed at identifying the nature of the effect of deformation waves from distant earthquakes on the geodynamic activity of the monitored rock mass are presented. The quantitative and energy characteristics of geoacoustic emission before and after the arrival of deformation waves in the controlled rock mass are analyzed. The analysis performed indicates a trigger mechanism of the influence of a distant earthquake on the geodynamic activity of the rock mass. It is noted that the direction of arrival of the deformation wave is an essential factor in the intensification of geodynamic activity in the rock mass. The experiments also revealed the characteristics of rock burst precursors when registering deformation waves in the low-frequency range.

The first results of unique experiments on the synchronous registration of seismic-strain oscillations of the Earth’s surface by three laser interferometers-deformographs (strainmeters) spaced 6740 km apart are presented. Two 100-meter laser interferometers at the Fryazino site (Moscow Region) and the 18-meter laser strainmeter at the observation point of Karymshina (Kamchatka Peninsula) were applied. The frequency-stabilized and thermally controlled lasers and the interferogram registration systems of compensation and modulation types providing an absolute instrumental resolution of 0.1-0.01 nm were used. The results of data analysis in sessions of synchronous operation of these instruments during 2016-2020 were obtained and discussed.

Since end of the 90s of the last century the seismological station Moxa was extended and developed into the modern Geodynamic Observatory. It comprises also the new installation of borehole-tilt meters in front of the observatory building and laser-strain meters in the gallery. The question arises how non-tidal signals are displayed in the measured time series. The investigation of such signals which can be caused naturally or man-made, can result in different sensitivities for the various tilt- and strainmeter systems, e.g. regarding barometric pressure impacts and hydrological induced pore pressure effects. Keywords: Tilt and strain observations, Non-tidal effects, Man-made effects, Pore-pressure, Induced tilt and strain, Geodynamic Observatory

A laser strainmeter with a 1500-m baseline was constructed at an underground site in Kamioka, Gifu Prefecture, Japan, and has been operating since August 2016. The laser interferometer measures the change in distance between two retroreflectors housed in two vacuum chambers with a separation of 1500 m. The retroreflectors are fixed to the ground in the tunnel of the KAGRA gravitational wave telescope. A high-frequency-stabilized laser is used as a light source; it achieves an Allan variance of 3 × 10−13. Since operations began, ground motions with large amplitude and timescale variations have been detected. The recorded tidal waveform almost agrees with the theoretical waveform; however, a slight difference of ~13% in amplitude is found, likely due to a topographic effect. The strain spectrum of the observed data for the 1500-m strainmeter indicates that the lowest background noise attained is less than 10−12 in the mHz band. Seismic waves up to 6 × 10−7 in amplitude have been observed without saturation or fringe steps. The strainmeter, with its excellent resolution, dynamic range, and bandwidth performance, provides a new method for observing low-frequency ground motion on seismic, geodetic, and intermediate timescales. Graphical Abstract A 1500-m laser strainmeter constructed at an underground site in Kamioka (left), calculated and observed earth tides (top right), and seismic waveform of an earthquake (Fukushima, Mw 6.9) occurred at 20:59:49 (UTC) on Nov. 21, 2016 (bottom right).

After a period of mild eruptive activity, Stromboli showed between 2017 and 2018 a reawakening phase, with an increase in the eruptive activity starting in May 2017. The alert level of the volcano was raised from “green” (base) to “yellow” (attention) on 7 December 2017, and a small lava overflowed the crater rim on 15 December 2017. Between July 2017 and August 2018 the monitoring networks recorded nine major explosions, which are a serious hazard for Stromboli because they affect the summit area, crowded by tourists. We studied the 2017–2018 eruptive phase through the analysis of multidisciplinary data comprising thermal video-camera images, seismic, geodetic and geochemical data. We focused on the major explosion mechanism analyzing the well-recorded 1 December 2017 major explosion as a case study. We found that the 2017–2018 eruptive phase is consistent with a greater gas-rich magma supply in the shallow system. Furthermore, through the analysis of the case study major explosion, we identified precursory phases in the strainmeter and seismic data occurring 77 and 38 s before the explosive jet reached the eruptive vent, respectively. On the basis of these short-term precursors, we propose an automatic timely alarm system for major explosions at Stromboli volcano.

SUMMARYThe strainmeter record observed at Isabella (ISA), California, for the 1960 Chilean earthquake (Mw = 9.5) is one of the most important historical records in seismology because it was one of the three records that provided the opportunity for the first definitive observations of free oscillations of the Earth. Because of the orientation of the strainmeter rod with respect to the back azimuth to Chile, the ISA strainmeter is relatively insensitive to G (Love) waves and higher order (order ≥ 6) toroidal modes, yet long-period G waves and toroidal modes were recorded with large amplitude on this record. This observation cannot be explained with the conventional low-angle thrust mechanism typical of great subduction-zone earthquakes and requires an oblique mechanism with half strike-slip and half thrust. The strain record at Ogdenburg, New Jersey, the Press–Ewing seismograms at Berkeley, California, and the ultra-long period displacement record at Pasadena, California, also support the oblique mechanism. We tested the performance of the ISA strainmeter using other events including the 1964 Alaskan earthquake and found no instrumental problems. Thus, the ISA observation of large G/R and toroidal/spheroidal ratios most likely reflects the real characteristics of the 1960 Chilean earthquake, rather than an observational artefact. The interpretation of the large strike-slip component is not unique, but it may represent release of the strike-slip strain that has accumulated along the plate boundary as a result of oblique convergence at the Nazca–South American plate boundary. The slip direction of the 2010 Chilean (Maule) earthquake ( Mw = 8.8) is rotated by about 10° clockwise from the plate convergence direction suggesting that right-lateral strain comparable to that of an Mw = 8.3 earthquake remained unreleased and accumulates near the plate boundary. One possible scenario is that the strike-slip strain accumulated over several great earthquakes like the 2010 Maule earthquake was released during the 1960 Chilean earthquake. If this is the case, we cannot always expect a similar behaviour for all the great earthquakes occurring in the same subduction zone and such variability needs to be considered in long-term hazard assessment of subduction-zone earthquakes.

We report on a detailed geodetic continuous monitoring in Timanfaya volcanic area (TVA), where the most intense geothermal anomalies of Lanzarote Island are located. We analyze about three years of GNSS data collected on a small network of five permanent stations, one of which at TVA, deployed on the island, and nearly 20 years of tiltmeter and strainmeter records acquired at Los Camelleros site settled in the facilities of the Geodynamics Laboratory of Lanzarote within TVA. This study is intended to contribute to understanding the active tectonics on Lanzarote Island and its origin, mainly in TVA. After characterizing and filtering out the seasonal periodicities related to “non-tectonic” sources from the geodetic records, a tentative ground deformation field is reconstructed through the analysis of both tilt, strain records and the time evolution of the baselines ranging the GNSS stations. The joint interpretation of the collected geodetic data show that the area of the strongest geothermal anomaly in TVA is currently undergoing a SE trending relative displacement at a rate of about 3 mm/year. This area even experiences a significant subsidence with a maximum rate of about 6 mm/year. Moreover, we examine the possible relation between the observed deformations and atmospheric effects by modelling the response functions of temperature and rain recorded in the laboratory. Finally, from the retrieval of the deformation patterns and the joint analysis of geodetic and environmental observations, we propose a qualitative model of the interplaying role between the hydrological systems and the geothermal anomalies. Namely, we explain the detected time correlation between rainfall and ground deformation because of the enhancement of the thermal transfer from the underground heat source driven by the infiltration of meteoric water., Projects CGL2015-63799-P of Spanish Ministry of Economy and Competitiveness, and 320/2011 of National Parks Autonomous Agency have supported this research.

Observations of surface deformation are essential for understanding a wide range of geophysical problems, including earthquakes, volcanoes, landslides, and glaciers. Current geodetic technologies, such as global positioning system (GPS), interferometric synthetic aperture radar (InSAR), borehole and laser strainmeters, are costly and limited in their temporal or spatial resolutions. Here we present a new type of strainmeters based on the coaxial cable Bragg grating (CCBG) sensing technology that provides cost-effective strain measurements. Two CCBGs are introduced into the geodetic strainmeter: one serves as a sensor to measure the strain applied on it, and the other acts as a reference to detect environmental noises. By integrating the sensor and reference signals in a mixer, the environmental noises are minimized and a lower mixed frequency is obtained. The lower mixed frequency allows for measurements to be taken with a portable spectrum analyzer, rather than an expensive spectrum analyzer or a vector network analyzer (VNA). Analysis of laboratory experiments shows that the strain can be measured by the CCBG sensor, and the portable spectrum analyzer can make measurements with the accuracy similar to the expensive spectrum analyzer, whose relative error to the spectrum analyzer R3272 is less than ±0.4%. The outputs of the geodetic strainmeter show a linear relationship with the strains that the CCBG sensor experienced. The measured sensitivity of the geodetic strainmeter is about −0.082 kHz/μe; it can cover a large dynamic measuring range up to 2%, and its nonlinear errors can be less than 5.3%.

International audience; Geodetic instruments now offer compelling sensitivity, allowing to investigate how solid Earth and surface processes interact. By combining surface air pressure data, nontidal sea level variations model, and rainfall data, we systematically analyze the volumetric deformation of the shallow crust at seven borehole strainmeters in Taiwan induced by 31 tropical cyclones (typhoons) that made landfall to the island from 2004 to 2013. The typhoon's signature consists in a ground dilatation due to air pressure drop, generally followed by a larger ground compression. We show that this compression phase can be mostly explained by the mass loading of rainwater that falls on the ground and concentrates in the valleys towards the strainmeter sensitivity zone. Further, our analysis shows that borehole strainmeters can help quantifying the amount of rainwater accumulating and flowing over a watershed during heavy rainfalls, which is a useful constraint for building hydrological models.

We have developed and built a highly accurate laser strainmeter for geophysical observations. It features the precise length measurement of a 100-m optical cavity with reference to a stable quantum standard. Unlike conventional laser strainmeters based on simple Michelson interferometers that require uninterrupted fringe counting to track the evolution of ground deformations, this instrument is able to determine the absolute length of a cavity at any given time. The instrument offers advantage in covering a variety of geophysical events, ranging from instantaneous earthquakes to crustal deformations associated with tectonic strain changes that persist over time. An automatic alignment control and an autonomous relocking system have been developed to realize stable performance and maximize observation times. It was installed in a deep underground site at the Kamioka mine in Japan, and an effective resolution of 2 × (10−8 − 10−7) m was achieved. The regular tidal deformations and co-seismic strain changes were in good agreement with those from a theoretical model and a co-located conventional laser strainmeter. Only the new instrument was able to record large strain steps caused by a nearby large earthquake because of its capability of absolute length determination.

Postseismic slip observed after large (M > 6) earthquakes typically has an equivalent moment of a few tens of percent of the coseismic moment. Some observations of the recurrence intervals of repeating earthquakes suggest that postseismic slip following small ( math formula) earthquakes could be much larger—up to 10 or 100 times the coseismic moment. We use borehole strain data from U.S. Geological Survey strainmeter SJT to analyze deformation in the days before and after 1000 1.9 < M < 5 earthquakes near San Juan Bautista, CA. We find that on average, postseismic strain is roughly equal in magnitude to coseismic strain for the magnitude range considered, suggesting that postseismic moment following these small earthquakes is roughly equal to coseismic moment. This postseismic to coseismic moment ratio is larger than typically observed in earthquakes that rupture through the seismogenic zone but is much smaller than was hypothesized from modeling repeating earthquakes. Our results are consistent with a simple, self-similar model of earthquakes.

To investigate short-term flow-pattern variations of a temperate glacier, longitudinal surface strain was measured with a wire strainmeter in the ablation area of Koryto glacier, Kamchatka, Russia. Strain-rate anomalies were observed in late summer 2000 that were triggered by a water overflow from a moulin near the measurement site followed by the drainage of accumulated water. The strain event started with (compressive) strain rates of >–10–3 d–1 lasting for 6 hours, which then became tensile. Similar strain-rate variations were observed again on the next day. During the event, basal sliding speed measured at the margin in the lower reach of the glacier fluctuated by about ±50% of the daily mean. Smaller and larger sliding speeds corresponded to the compressive and tensile surface strains, respectively. These measurements suggest that the storage and sudden drainage of water caused spatially non-uniform water-pressure fluctuations along the glacier, changing the sliding regime over short time periods.

International audience; High-resolution borehole strainmeters are usually installed in tectonically active regions in order to detect slow-slip events, and to estimate slow transients related to earthquake swarms. However, they are also sensitive to other numerous influences, internal or external. Furthermore, the quality of their coupling to the rock through cementation, and the mechanical properties of the rock mass around them, have a critical influence on their records. Many of the existing strainmeters present such problems, and the correction for these effects often remains a challenge. In this paper, we present the analysis of the records of a high-resolution borehole dilatometer (Sacks–Evertson), located in the seismically active rift of Corinth (Greece) (station TRZ in the Trizonia island). We show that the instrument suffers from an only partial-solid coupling, and that the nearby sea tides have a direct (through elastic response) and indirect (through pore-pressure diffusion) effect on the dilatation signal, which adds up to the solid tidal strain source. We propose a methodology that allows, in a first step, to better separate the internal (solid tide) from the external (air pressure, sea level) influences, by calculating a frequency-dependent transfer function outside the range of the tidal periods. We then extrapolate this function, in particular at the tidal periods. In a second step, the resulting variation with frequency of the coupling coefficients with sea level led us to estimate the proportion of instrument not solidly cemented to rock (thus in contact with water pore pressure), which is about 90 % of the total height. Despite the small proportion of solid coupling, the sensor resolution remains very good up to a few tens of hours of a time period, thanks to the confining effects of the rocks on the local pore pressure. These results allow us to correct for the external effects, and reduce the associated variance by 80–90 % (in the period range of minutes to days). The empirical correction of the sea level effect could be explained using a simple Boussinesq’s approximation and 1D pore-pressure diffusion model, which contributed to better constraint of some of the poro-elastic parameters in the vicinity of the instrument. After correction, the solid tidal signal at the 24-h period is almost anti-correlated with those of the theoretical solid tide. This surprising result is consistent with a similar anti-correlation observed for the longest period surface waves (200 s) comparing the TRZ dilatometer signals to the strain measured by a nearby borehole strainmeter (MOK, 15 km). This could be related to the presence of a shallow fault close to the instrument, which would creep in response to seismic wave-related stress.

International audience; This paper presents the örst analysis of the records of an elliptical 3-component Sacks-Evertson borehole strainmeter. This high-resolution prototype by the Carnegie Institution of Washington, is installed since 2006 in the western rift of Corinth, Greece. We örst present the calibration and the correction from external inøuences, in order to quantify the detection level of the instrument. We show evidence for pore pressure diffusion from the sea, mostly affecting one component. Neglecting this effect, a örst order correction reduces the signal by 90% at tidal periods for 2 components and about 70% for the third one. The residual noise vary from 1 nstrain at 1-hour period to 10 nstrain at 1-day period. It allows to detect slow earthquakes lasting 1 day down to magnitude 4 at an hypocentral distance of 8 kilometers. The uncorrected records at periods smaller than semidiurnal does not reveal any slow strain transient with strong amplitude. During the closest seismic swarm to the site in 2011, the analysis of the records reveals strain steps occuring at the arrival times of seismic waves radiated by the local earthquakes, uncorrelated with the amplitudes and mostly related to dynamic pore pressure instabilities.

The aim of the study presented in this paper is to develop a flexible network structure for temperature monitoring of a super high arch dam under construction period. The multiple channel temperature acquisition method collects and analyzes system including flexible and stable field bus for the sensors, communication between intelligent module and control unit is proposed. In this temperature monitoring system, a total of 3 kinds of networks which independently marked by ∗ (1), ∗ (2), and ∗ (3) were proposed, with ∗ (1) being the lowest priority and ∗ (3) being the highest priority. The lowest priority is field bus (ITU Bus) which connects all the grouped sensors into different channels of different intelligent acquisition modules. The ITU network protocol is a star type, and the network structure is independent on the sensors. The bus can connect different types of sensors such as strainmeter, stressmeter, jointmeter, rock-deformeter, piezometer et al., the measurement scope could be extended wider. This study provides a measuring technique has been successfully implemented in monitoring of the Xiluodu arch dam construction, and ultimately solved the shortcoming of manual measurement technique.

[1] We analyze the volcano seismicity recorded during the pre- and co-eruptive regimes of the 2007 effusive crisis at Stromboli volcano (Italy). Data-set is composed of the continuous recordings of a three-component broad-band seismometer and of a Sacks-Evertson strainmeter. Starting from the characterization of the non effusive phase as a stationary state of equilibrium, we investigate the effusive phase as a non-equilibrium state. A statistical analysis reveals that the explosion occurrence is always driven by a nearly Poissonian process, as for the standard activity, even during the effusive phase, with the only difference in shortening the inter-times. Explosion-quake amplitudes are lognormally distributed until the effusive phase, becoming then broader. This indicates that many scales are involved. A slightly different process can be advocated for the swarms of the explosions occurring during the effusive phase. This suggests that the dynamics of the exsolution and/or aggregation of the gas slugs should differ from the nucleation mechanism responsible of the standard Strombolian activity. The pre-eruptive regime is characterized by a very long deformative signal that appears as a transient oscillating signal with a period of about three days that modulates the explosion amplitudes. In a conceptual vibrating cavities model, it is related to a chocking phenomenon induced by magma injection, which in turn leads to the effusion.

An underground low-noise high-sensitivity laser strainmeter, crossing a fault in the Gran Sasso massif (central Italy), is discontinuously operating since late May 1994, after a few years of mechanical stabilization of end monuments. A swift extensional strain transient reaching a peak of at least 1 μϵ occurred in about one month from the beginning of the operating time, followed by a four-month-long coarsely stable period, and a slower decay. On June 2nd 1994, in coincidence with two local earthquakes, permanent extensional offsets of about 10 ne have been recorded. A further aseismic slip of the same order of magnitude and sign has been observed about thirty minutes after the last preceding local event, and ten minutes before the next following one. At the same time, the arrival of seismic waves from a distant earthquake has been recorded by the interferometer. No similar signal behaviour has been observed any more since then.

Four invar-wire strainmeters have been operated in shallow trench sites for 19 months beside the San Andreas Fault at Parkfield, California. Temperature and rainfall records were correlated with 1 yr of strainmeter data, and 90 per cent of the strain signal power at periods between 2 and 120 days was predicted entirely from these records, using a multi-channel, Wiener filtering technique. The residual strain series fluctuates with a peak-to-peak amplitude of nearly 10−6 strain. Anomalous strain signals taking place over several days would have to be larger than this to be identifiable. Previous work shows that signals of amplitude 10−7 strain are identifiable if they take place within hours. Deep creep events giving rise to such signals, which may occur as precursors to earthquakes, would need to be very large.Other workers have shown that shallow, short-base line tiltmeters in California are also very sensitive to meteorological noise. Strainmeter and tiltmeter installations can be made less sensitive to meteorological noise, either by manufacturing instruments with long (∼1 km) base lines, or by using tunnel or borehole sites (≳100 m deep). Proven instruments of these types are costly, unless an underground site was already available. However, if networks of shallow, shortbase line strainmeters or tiltmeters are to be used for earthquake prediction, it is obviously desirable to invest in at least a few installations which are less sensitive to noise of meteorological origin.