Crustal Strain Changes Research Articles

The Strain State Analysis of 4-component Borehole Strainmeter Observations in Sichuan-Yunnan Region

Analysis of nearly a decade of crustal strain changes state after the Ms8.0 Wenchuan earthquake by using 4-component borehole strain observation data, and combined with the tectonic stress field, this paper studied the regional stress and strain variation characteristics and dynamics. The results show that the main compressive strain direction of the 4-component borehole strain observation is approximately the same as that of tectonic stress field. However, there are also some regional inconsistencies, which should be related to regional structural features.

Temporal velocity variations in the northern Hikurangi margin and the relation to slow slip

Slow slip events (SSE) have been studied in increasing detail over the last 20 years, improving our understanding of subduction zone processes. Although the relationship between SSEs and the physical properties of their surrounding materials is still not well-understood, the northern Hikurangi margin in New Zealand is the site of relatively shallow (<10 km deep), frequent SSEs, providing excellent opportunities for near-field investigations. From September to October 2014, an SSE occurred with more than 250 mm slip, and was recorded successfully by the Hikurangi Ocean Bottom Investigation of Tremor and Slow Slip (HOBITSS) deployment. This study applies scattered wave interferometry to ambient noise data acquired by nine HOBITSS ocean bottom seismometers (OBS) to study the seismic velocity variations related to the SSE. Single station cross-component correlations are computed within a period band that focuses on the upper plate in our study region. The average velocity variations display a decrease on the order of 0.05% during the SSE, followed by an increase of similar magnitude afterwards. We suggest two possibilities. The first possibility, which has been suggested by other seismological observations, is that the SSE causes a low-permeability seal on the plate boundary to break. The break allows fluid to migrate into the upper plate, causing a seismic velocity decrease during the SSE because of increased pore fluid volume in the upper plate. Under this model, after the SSE, the fluids in the upper plate diffuse gradually and the velocity increases again. The second possibility is the velocity changes are related to changes in crustal strain during the slow slip cycle, whereby elastic strain accumulates prior to the SSE, causing contraction and reduction of porosity and therefore increase of velocity above the SSE source (the seismic velocity increases between SSEs). During the SSE the upper plate goes into extension as the elastic strain is released, which results in dilation and a porosity increase (seismic velocity reduction). After the SSE, stress and strain accumulate again, causing a porosity decrease and a velocity increase.

New Possible Earthquake Precursor and Initial Area for Satellite Monitoring

We propose a new possible earthquake precursor, a coastal water jet originating from shallow water gas seeps and colored by sediments, lifted from increased gas seeps emissions, preceding some earthquakes with offshore epicenters along the Bulgarian Black Sea coast and M ≥ 3. The new possible earthquake precursor is site specific and may be observed in shallow coastal water regions where active faults are accompanied by hydrocarbon gas seeps. We point out to a region where it can be easily detected by direct observation and satellite remote sensing, Zelenka methane seeps (ZMS), near the Bulgarian Black Sea coast. The ZMS activation is related to the tectonic stress and fracturing preceding and accompanying the earthquakes in the Shabla-Kaliakra-Balchik region along the northern part of the Bulgarian Black Sea coast. We also propose an earthquake forecasting experiment, based on the following four hypotheses: 1) The change of the methane emission of shallow horizons is related to crustal strain changes preceding earthquakes in the region; 2) extreme change of the activity of underwater methane seepages appears immediately before nearby earthquakes; 3) shallow water methane seepages activity can be monitored by remote sensing; 4) satellites can register effects from an extreme increase in their emissions. The proposed earthquake forecasting experiment is based on the monitoring of methane seepages activity in the ZMS area by direct observation and remote sensing which may provide indication for preparatory earthquake activity preceding offshore earthquakes in the region.

Detection of groundwater flux changes in response to two large earthquakes using long-term bedrock temperature time series

Heat as a groundwater tracer has potential application in identifying earthquake-induced changes in fluid flow. Since convective heat transport modifies the phase and amplitude of periodic oscillations under pure heat conduction condition, temporal variation of groundwater flux can thus be derived from multi-depth periodic temperature signals. Here we present groundwater flux changes after two large earthquakes nearby, determined from in situ bedrock temperature measurements in the Xianshuihe fault zone, at the eastern margin of the Tibetan Plateau. Five-year temperature time series at six different locations are recorded by high sensitivity temperature sensors (10−4 K) installed at various depths ranging from 0 to 20 m. Groundwater fluxes are estimated through time-varying amplitudes and phases of the annual oscillations, extracted from the Dynamic Harmonic Regression technique. Results show different hydrological responses to these two earthquakes. After the 2013 Ms 7.0 Lushan earthquake, sustained rise in upward flux was revealed at all locations in the intermediate-field, contradicting to the modeled coseismic static dilatational strains. However, groundwater flux patterns after the 2014 Ms 6.3 Kangding earthquake are consistent with the coseismic volumetric strain distribution of a quadrantal pattern of this event. We propose that enhanced hydraulic permeability by dynamic stress might cause the increased upward fluid flux after the Lushan earthquake in the intermediate-field, while coseismic static volumetric strain may account for the hydrological changes after the Kangding earthquake in the near-field. This is the first time that temperature–time series are used to quantify continuous earthquake-related changes in groundwater fluxes. In situ temperature monitoring can provide insights into earthquake-driven hydrologic responses, and also offer additional information to identify temporal changes in crustal strain or hydraulic properties.

High Temporal Resolution Monitoring of Small Variations in Crustal Strain by Dense Seismic Arrays

AbstractWe demonstrate the feasibility of detecting very weak deformation in the shallow crust with high temporal resolution by monitoring the relative changes in seismic wave velocity (dv/v) using dense arrays of seismometers. We show that the dv/v variations are consistent between independent measurements from two seismic arrays. Dominant peaks in the observed dv/v spectrum suggest that tides and temperature changes are the major causes of daily and subdaily velocity changes, in accordance with theoretical strain modeling. Our analysis illustrates that dv/v perturbations of the order of 10−4, corresponding to crustal strain changes of the order of 10−8, can be measured from ambient seismic noise with a temporal resolution of 1 hr. This represents a low‐cost technique for high precision and high time‐resolution monitoring of crustal deformation that is complementary to existing geodetic measurements and is instrumental in both the detection and understanding of low‐amplitude precursory processes of natural catastrophic events.

Establishing the range of background for radon variations in groundwater along the Serghaya fault in southwestern Syria

Long-term groundwater radon measurements were carried out in two selected karstic springs emerging from the Serghaya fault zone in southwestern Syria. The work is aimed at determining the range of radon background along the concerned fault, which represents a prominent branch segment of the Dead Sea Fault System in the region. The obtained data was statistically analyzed and the mean radon values have been standardized in terms of probability of magnitude in order to enable the separation between normal radon variations from other anomalous or geotectonic related values. The results revealed a general background range of radon concentration varying between 5000 and 13000 Bqm-3, and thus all radon values lying outside this range were considered anomalous. However, remarkable clusters of high radon concentrations with peak values more than twice times the background level, were observed in both monitoring springs through the period (1992-1994). These abnormal radon values were positively correlated with simultaneous time of high precipitations, while no significant earthquake activities were recorded in the region during that period. Therefore, such radon signals do not seem to be a reflection of regional changes in crustal strain, but rather they mostly indicate evidences of radon response to the groundwater table fluctuations due to high precipitations. These consequences may confirm the usefulness of radon application as an important natural tracer in hydrogeological investigations.

Long-term Crustal Strain Changes Observed in the Northern Part of the Kinki District, Japan

近畿地方北部の敦賀・今津観測点においてボアホール型3成分歪計による観測が行われている。両観測点で得られた1996年から12.5年間のデータについて調べた。今津のデータに見られる季節変動は並行観測されている地下水位との相関が高く、敦賀のデータに見られる季節変動は降水量を入力としたタンクモデルを使って説明することができた。設置後の安定化過程を指数関数で近似し、これを除去した。季節変動、指数関数的減衰過程を除去した歪変化には、2000年頃と2005年頃に歪速度変化が見られる。この歪速度変化は機器の感度変化、および降水量の長期的変化では必ずしも説明できない。東海地域で同時期に発生したゆっくりすべりによって生じうる歪を計算して観測された非定常的な歪変化と比較したところ、歪の大きさは観測値の方が1桁大きいが主歪の方向は整合的だった。

Seismicity, deformation and seismic hazard in the western rift of Corinth: New insights from the Corinth Rift Laboratory (CRL)

This paper presents the main recent results obtained by the seismological and geophysical monitoring arrays in operation in the rift of Corinth, Greece. The Corinth Rift Laboratory (CRL) is set up near the western end of the rift, where instrumental seismicity and strain rate is highest. The seismicity is clustered between 5 and 10 km, defining an active layer, gently dipping north, on which the main normal faults, mostly dipping north, are rooting. It may be interpreted as a detachment zone, possibly related to the Phyllade thrust nappe. Young, active normal faults connecting the Aigion to the Psathopyrgos faults seem to control the spatial distribution of the microseismicity. This seismic activity is interpreted as a seismic creep from GPS measurements, which shows evidence for fast continuous slip on the deepest part on the detachment zone. Offshore, either the shallowest part of the faults is creeping, or the strain is relaxed in the shallow sediments, as inferred from the large NS strain gradient reported by GPS. The predicted subsidence of the central part of the rift is well fitted by the new continuous GPS measurements. The location of shallow earthquakes (between 5 and 3.5 km in depth) recorded on the on-shore Helike and Aigion faults are compatible with 50° and 60° mean dip angles, respectively. The offshore faults also show indirect evidence for high dip angles. This strongly differs from the low dip values reported for active faults more to the east of the rift, suggesting a significant structural or rheological change, possibly related to the hypothetical presence of the Phyllade nappe. Large seismic swarms, lasting weeks to months, seem to activate recent synrift as well as pre-rift faults. Most of the faults of the investigated area are in their latest part of cycle, so that the probability of at least one moderate to large earthquake ( M = 6 to 6.7) is very high within a few decades. Furthermore, the region west to Aigion is likely to be in an accelerated state of extension, possibly 2 to 3 times its mean interseismic value. High resolution strain measurement, with a borehole dilatometer and long base hydrostatic tiltmeters, started end of 2002. A transient strain has been recorded by the dilatometer, lasting one hour, coincident with a local magnitude 3.7 earthquake. It is most probably associated with a slow slip event of magnitude around 5 ± 0.5. The pore pressure data from the 1 km deep AIG10 borehole, crossing the Aigion fault at depth, shows a 1 MPa overpressure and a large sensitivity to crustal strain changes.

Detection of Aseismic Slip on an Inland Fault by Crustal Movement and Groundwater Observations: A Case Study on the Yamasaki Fault, Japan

To understand the detailed process of fault activity, aseismic slip may play a crucial role. Aseismic slip of inland faults in Japan is not well known, except for that related to the Atotsugawa fault. To know whether aseismic slip does not occur, or is merely not detected, is an important question. The National Institute of Advanced Industrial Science and Technology constructed an observation site near Yasutomi fault, a part of the Yamasaki fault system, and has collected data on the crustal strain field, groundwater pressures, and crustal movement using GPS. In a departure from the long-term trend, a transient change of the crustal strain field lasting a few months was recorded. It indicated the possibility of an aseismic slip event. Furthermore, analyses of data from the extensometers at Yasutomi and Osawa observation vaults of Kyoto University, as well as GPS data from the Geographical Survey Institute (GEONET), revealed unsteady crustal strain changes. All data could be explained by local, left-lateral, aseismic slip of the order of 1 mm in the shallow part of the Yasutomi fault.

Groundwater Anomalies Associated with the 1995 Hyogo-ken Nanbu Earthquake.

There have been many reports on earthquake-induced groundwater anomalies, but the mechanism of these anomalies is not very clear. The 1995 Hyogo-ken Nanbu earthquake, which occurred on January 17, 1995, was one of the greatest shallow inland earthquakes in Japan since the modern Japanese observation system for monitoring seismicity was established. Many groundwater anomalies have been observed following this earthquake. Our purpose was to study these anomalies systematically and to gain some knowledge of their mechanisms. We initiated a questionnaire survey in and around the source region on March 8, 1995. We also investigated the discharging waters which appeared on Awaji Island after the Hyogo-ken Nanbu earthquake. These results were compared with the volumetric strain changes estimated from fault models for the earthquake which stretch in a SW-NE direction. Many post-seismic rises in the level or discharge of groundwater as well as a few post-seismic drops were detected by the questionnaire and the investigation. However, their distribution did not coincide with the distribution of the volumetric strain changes, which are of a quadrantial type because the fault models are of a right-lateral strike-slip type. Several precursory groundwater anomalies were also reported, although few pre-seismic crustal strain changes were observed. Therefore, the volumetric strain changes do not always explain the groundwater anomalies that accompanied the 1955 Hyogo-ken Nanbu earthquake.

Changes in Crustal Strain and Hot Spring Temperature as Related to Volcanic Eruptions.

Variations in the crustal strain at two stations and water temperatures at four hot springs have been continuously monitored in the Izu Peninsula. For the 1986 Izu-Oshima eruption, the temporal . variations of a strain meter at Yugashima showed a good correlation with the cumulative discharge of magma from the summit crater of the volcano. The strain meters of all components at two stations showed the extension during the fissure eruption of November 21. The temperature variations at Shimosagano hot spring had a fairly good correlation with the cumulative discharge of the eruption. The hot spring temperature at Yugano abruptly dropped 25 days before the fissure eruption. For the 1989 Ito-oki swarm earthquake, the strain meters at two stations showed an extension or contraction. The hot spring temperature at Shimosagano increased in conjunction with this earthquake sequence. The hot spring temperature at Yugano abruptly dropped 2.3 days before the 1989 Ito-oki eruption. On the other hand, neither strain nor hot spring temperature changed in the case of the 1989 Ito-oki eruption. The extensions observed in the Izu Peninsula at the time of this period of the 1986 Izu-Oshima eruption can be explained by a decrease in the magma pressure. Therefore, no strain change during the 1989 Ito-old eruptions suggests that the amount of discharge might have been so little that the magma pressure was scarcely reduced at the source. Although the abrupt changes in hot spring temperature were not directly correlated with the eruptions, they may rapidly reflect movements of the magma.

Anomalous strain response to rainfall in relation to earthquake occurrence in the Tokai area, Japan.

The effect of rainfall on crustal strain at the Mikawa Crustal Movement Observatory, central Japan, was studied in detail with a data set from January 1974 through December 1984. Changes in crustal strain caused by rainfall were successfully simulated by a tank model, in which the crustal strain is given as a nonlinear function of precipitation and time. The simulation error was usually less than 10%, but occasionally it became larger. There were anomalies of two kinds: 1) a change in spatial distribution of strains in the observation tunnel; and 2) an increase in simulation error for the rainfall effect. These anomalous responses seem to be related to the occurrence of nearby earthquakes within a particular area around the observatory. The logarithmic duration time of anomaly was roughly proportional to the earthquake magnitude. Data from the past eleven years indicate that about 50% of M ≥ 3.5 earthquakes in the area were preceded by anomalous strain responses if they occurred after rain. The change in strain response to rainfall at this observatory could be a precursor of a nearby earthquake.

On radon emanation as a possible indicator of crustal deformation

(Accepted for publication March 24, 1978) ABSTRACT: Radon emanation has been monitored in shallow capped holes by a Tracketch method along several active faults and in the vicinity of some volcanoes and underground nuclear explosions. The measured emanation shows large temporal variations that appear to be partly related to crustal strain changes. This paper proposes a model that may explain the observed tectonic variations in radon emanation, and explores the possibility of using radon emanation as an indicator of crustal deformation. In this model the emanation variation is assumed to be due to the perturbation of near-surface profile of radon concentration in the soil gas caused by a change in the vertical flow rate of the soil gas which, in turn, is caused by the crustal deformation. It is shown that, for a typical soil, a small change in the flow rate (3 · 10 +4 cm sec +1 ) can effect a significant change (a factor of 2) in radon emanation detected at a fixed shallow depth (0.7 m). The radon concentration profile has been monitored at several depths at a selected site to test the model. The results appear to be in satisfactory agreement.

弾性定数変化に伴う地殻ひずみの変化

弾性定数変化に伴う地殻ひずみの変化

Tectonics of the San Andreas Fault System seismological studies

The primary objectives of the current seismological program of the National Center for Earthquake Research (NCER) include: (1) evaluation of the use of well recorded aftershock sequences to delineate the slip surfaces associated with large earthquakes, (2) determination of the degree to which microearthquakes are confined to (and therefore delineate) the major faults that traverse the region of central California between the Gabilan range and San Francisco Bay, and (3) investigation of the space‐time‐energy relationships among microearthquakes and of the relation of crustal strain changes to the earthquake regime in central California.Thirty‐two short‐period vertical seismometers are installed in four clusters in key localities along the San Andreas and associated faults in central California. Telemetered signals from these seismometers are recorded in compact format on three Develocorders at the NCER office building in Menlo Park, where reading and analysis of the seismograms are kept current. Hypocenters are determined by computer, using crustal models based on local refraction surveys and station corrections based partly on teleseism P‐wave delays and partly on average residuals for a large number of local earthquakes. Computer cards that summarize the principal parameters of each earthquake are collected in a card library to facilitate analysis of the earthquakes and the study of their relation to measured changes in crustal strain.