Borehole Strain Research Articles

Volcano Deformation and Gravity Workshop Synopsis and Outcomes: The 2008 Volcano Deformation and Temporal Gravity Change Workshop; Vancouver, Washington, 13–15 May 2008

A volcano workshop was held in Washington State, near the U.S. Geological Survey (USGS) Cascades Volcano Observatory. The workshop, hosted by the USGS Volcano Hazards Program (VHP), included more than 40 participants from the United States, the European Union, and Canada. Goals were to promote (1) collaboration among scientists working on active volcanoes and (2) development of new tools for studying volcano deformation. The workshop focused on conventional and emerging techniques, including the Global Positioning System (GPS), borehole strain, interferometric synthetic aperture radar (InSAR), gravity, and electromagnetic imaging, and on the roles of aqueous and magmatic fluids.

New borehole strain system detects uplift at Campi Flegrei

Campi Flegrei and Mount Vesuvius are active Italian volcanoes though presently in aquiescent stage. The last eruption of Mount Vesuvius occurred during the spring of 1944. Campi Flegrei last erupted in 1538 but experienced a subsidence trend from the early 1900s to 1970, which was followed by episodes of ground uplift accompanied by seismic swarms [see, e.g., Aster et al., 1992].Over the past 37 years at Campi Flegrei, about 4 meters of maximum ground uplift has occurred followed by about 1 meter of subsidence, as measured near the center of the caldera in two episodes during 1970–1972 and 1982–1984. This deformation has occurred close to the harbor of the town of Pozzuoli, putting about 400,000 people at heightened risk. From 1985 to 2004, Campi Flegrei's caldera showed gradual subsidencethat was interrupted by five mini‐uplift episodesin 1976, 1989, 1995, 2000, and, most recently, 2004–2006, each amounting to a few centimeters of uplift [Pingue et al., 2006]. The caldera is generally aseismic during gradual subsidence, but small swarms of microearthquakes are produced during periods of elevated strain rates associated with the mini‐uplift episodes [Saccorotti et al., 2001 ].

Changes in groundwater levels or pressures associated with the 2004 earthquake off the west coast of northern Sumatra (M9.0)

Abstract Associated with the 2004 earthquake off the west coast of northern Sumatra, changes in groundwater levels or pressures were observed at many observation stations in Japan which are more than 5000 km from the hypocenter. At 38 of the 45 observation stations, there were changes in groundwater levels or pressures. At the 10 observation stations in which the Ishii-type borehole strain instruments were established, changes in crustal strains were also observed. A major part of the changes in crustal strains and groundwater levels or pressures were dynamic oscillations due to a seismic wave. At some stations, coseismic or postseismic rises or drops were also observed. At five stations where both crustal stain and groundwater levels or pressures were observed, postseismic changes in groundwater levels or pressures were consistent with coseismic static steps in crustal strains. At the other five stations, postseismic changes in groundwater levels or pressures did not agree with the coseismic static steps. At two stations of these five stations, it is anticipated that the pore water pressure change in each aquifer locally occurred independently of the change in crustal strain. At another station, postseismic changes in groundwater level possessed the same characteristics as a model removing the temporary deposition. At the last two stations, the causes of the changes are unknown.

Continuous Borehole Strain and Pore Pressure in the Near Field of the 28 September 2004 M 6.0 Parkfield, California, Earthquake: Implications for Nucleation, Fault Response, Earthquake Prediction, and Tremor

Near-field observations of high-precision borehole strain and pore pres- sure, show no indication of coherent accelerating strain or pore pressure during the weeks to seconds before the 28 September 2004 M 6.0 Parkfield earthquake. Minor changes in strain rate did occur at a few sites during the last 24 hr before the earth- quake but these changes are neither significant nor have the form expected for strain during slip coalescence initiating fault failure. Seconds before the event, strain is stable at the 10 � 11 level. Final prerupture nucleation slip in the hypocentral region is constrained to have a moment less than 2 � 10 12 Nm( M 2.2) and a source size less than 30 m. Ground displacement data indicate similar constraints. Localized rupture nucleation and runaway precludes useful prediction of damaging earthquakes. Coseismic dynamic strains of about 10 microstrain peak-to-peak were superimposed on volumetric strain offsets of about 0.5 microstrain to the northwest of the epicenter and about 0.2 microstrain to the southeast of the epicenter, consistent with right lateral slip. Observed strain and Global Positioning System (GPS) offsets can be simply fit with 20 cm of slip between 4 and 10 km on a 20-km segment of the fault north of Gold Hill (M 0 � 7 � 10 17 N m). Variable slip inversion models using GPS data and seismic data indicate similar moments. Observed postseismic strain is 60% to 300% of the coseismic strain, indicating incomplete release of accumulated strain. No measurable change in fault zone compliance preceding or following the earthquake is indicated by stable earth tidal response. No indications of strain change accompany nonvolcanic tremor events reported prior to and following the earthquake.

Study on relationship between features of strain anomaly obtained by borehole strain meter at Wushi station in Xinjiang and strong earthquake: Taking Jiashi M s=6.8 earthquake as an example

The borehole strain meter at Wushi station recorded obvious anomaly before Jiashi M s=6.8 earthquake occurred on February 24, 2003. Its features are as follows. (1) Anomaly types are complete. The trend anomaly, short-term anomaly, short-imminent anomaly and exponential anomaly appeared 19 months, 56 days, 4 days, and more than 1 month before the event, respectively; (2) Anomaly is large in magnitude. The maximal magnitude of strain anomaly is 1.7×10−5, which is rare in the past 20-year observation records at Wushi station; (3) Strain rate fluctuates sharply with obvious alternation of tension and compression. According to the magnitude of strain anomaly, time of exponential anomaly appearance and regional features of recorded anomaly, we could predict the magnitude, occurrence time and potential region to a certain degree.

Developments of borehole strain observation outside China

Borehole strain observation is playing an increasingly important role in the study on the crustal movements. It has been used by many countries such as China, USA, Japan, Peru, Australia, South Africa, Iceland and Italy, in research fields of plate tectonics, earthquake, volcanic eruption, dam safety, oil field subsidence, mining collapse and so on. Borehole strainmeter has been improved rapidly and tends to get more and more components included in one probe. Based on observations by this kind of instruments, studies on seismic strain step, slow earthquake, earthquake precursor and volcanic eruption forecasting have made remarkable achievements. In the coming years, borehole strain observation is going to become one major goedetic means, together with GPS and InSAR.

Application of observed strain steps to the study of remote earthquake stress triggering

A study of the Kunlunshan earthquake of MS=8.1 based on observed coseismic strain steps from the borehole strain monitoring network over China has been carried out with some interesting results. Firstly, many recordings disagree with theoretic calculation using static dislocation model. Secondly, abnormally large strain steps are observed at quite a few stations in the tectonically active east-northern China, while in the relatively inactive east-southern China no obvious steps are recorded. It is inferred that seismic stress triggering may significantly affect remote seismic strain field. In other words, whether remote faulting be seismically triggered or not may determine the pattern of local seismic strain changes. Further comparison study results of March 11, 1999 Zhangbei earthquake and November 1, 1999 Datong earthquake show that the specific pattern of seismic zones has obvious influence on seismic strain changes in the region. This supports the idea that observed abnormal strain steps might be produced by coseismicly stress-triggered local faulting.

Triggered Deformation and Seismic Activity under Mammoth Mountain in Long Valley Caldera by the 3 November 2002 Mw 7.9 Denali Fault Earthquake

The 3 November 2002 Mw 7.9 Denali fault earthquake triggered defor- mational offsets and microseismicity under Mammoth Mountain (MM) on the rim of Long Valley caldera, California, some 3460 km from the earthquake. Such strain offsets and microseismicity were not recorded at other borehole strain sites along the San Andreas fault system in California. The Long Valley offsets were recorded on borehole strainmeters at three sites around the western part of the caldera that includes Mammoth Mountain—a young volcano on the southwestern rim of the caldera. The largest recorded strain offsets were 0.1 microstrain at PO on the west side of MM, 0.05 microstrain at MX to the southeast of MM, and 0.025 microstrain at BS to the northeast of MM with negative strain extensional. High sample rate strain data show initial triggering of the offsets began at 22:30 UTC during the arrival of the first Rayleigh waves from the Alaskan earthquake with peak-to-peak dynamic strain amplitudes of about 2 microstrain corresponding to a stress amplitude of about 0.06 MPa. The strain offsets grew to their final values in the next 10 min. The associated triggered seismicity occurred beneath the south flank of MM and also began at 22:30 UTC and died away over the next 15 min. This relatively weak seismicity burst included some 60 small events with magnitude all less than M 1. While poorly constrained, these strain observations are consistent with triggered slip and intrusive opening on a north-striking normal fault centered at a depth of 8 km with a moment of 10 16 N m, or the equivalent of a M 4.3 earthquake. The cumulative seismic moment for the associated seismicity burst was more than three orders of magnitude smaller. These observations and this model resemble those for the triggered deformation and slip that occurred beneath the north side of MM following the 16 October 1999 M 7.1 Hector Mine, California, earthquake. However, in this case, we see little post-event slip decay reflected in the strain data after the Rayleigh-wave arrivals from the Denali fault earthquake and onset of triggered seismicity did not lag the triggered defor- mation by 20 min. These observations are also distinctly different from the more widespread and energetic seismicity and deformation triggered by the 1992 M 7.3 Landers earthquake in the Long Valley caldera. Thus, each of the three instances of remotely triggered unrest in Long Valley caldera recorded to date differ. In each case, however, the deformation moment inferred from the strain meter data was more than an order of magnitude larger than the cumulative moment for the associated triggered seismicity.

A New Instrument To Remotely Monitor Rock Mass Deformation

A new system for precise monitoring of surface and underground deformations in rock mass surrounding a mining operation has been developed and successfully deployed by CSIRO Exploration and Mining since 1993. The new system is based on a borehole strainmeter, which has the sensitivity to enable measurements remote (for example at distances of 1-5 km) from the mining operation, and long term stability to provide accurate measurements over periods of years. Strainmeters traditionally used for deformation measurement have neither the long-term stability nor the high sensitivity to perform measurements in these applications. This paper describes the new precision borehole strain monitoring system (GTS) currently deployed by CSIRO Exploration and Mining, which has the potential to solve these new issues in rock mass deformation monitoring. This technology was originally developed for use in hard rock mines (Gladwin 1977) and refined considerably for earthquake research (Gladwin et al. 1994, Gwyther et al., 1992). A case study of the use of the GTS in monitoring longwall coal mining over the period 1993-1999 is presented. Accurate measurement of rock mass response during the mining of massive underground ore-bodies is essential as mines become larger and deeper. The CSIRO GTS system is immediately applicable in circumstances such as: provision of quantitative data for optimal pit slope design and engineering; measurement of the stability of deep pit slopes, monitoring the long term integrity of shafts, large scale underground infrastructure and surface infrastructure, and long term measurements of deformation or rock mass creep following the mining process to provide data for environmental management.

Creep rate changes at Parkfield, California 1966–1999: Seasonal, precipitation induced, and tectonic

Measured fault creep at Parkfield contains information about the slip rate on the San Andreas fault but also is affected by rainfall and other seasonal effects. Seven creep meters record a repeatable seasonal variation that can be removed from the data. Four of the creep meters exhibit surges in creep rate during the rainy season. For these instruments a function of rainfall is developed that crosses a threshold within a few days of the onset of accelerated creep. In addition to the seasonal variations and surges, most Parkfield creep meters record higher creep rates more frequently during the wet season than during the dry season. Characterizing this behavior makes it possible to distinguish between rainfall‐influenced creep and creep rate changes of tectonic origin. Accelerated creep beginning in January 1983 was probably induced by rainfall, rather than by tectonic sources related to the Coalinga earthquake in May 1983. Four creep meters in the central part of the Parkfield fault segment are recording higher creep rates since 1993. A strong case can be made that the increased creep rate at CRR1 is tectonic, but for the other three creep meters an influence of rainfall is difficult to rule out. Strain rate changes recorded on three‐component borehole strain meters suggest that the rate of subsurface creep to the northwest of these instruments is even greater. The 1993 creep rate increase is more abrupt and farther south than the expected signal from accelerating slip near the hypocenter of the 1966 Parkfield earthquake but is in the same location as rapid fault slip reported prior to that event.

Predictions of the 1997 strong earthquakes in Jiashi, Xinjiang, China

Abstract A sequence of strong earthquakes occurred in Jiashi County, Xinjiang, China (40°N, 77°E, population 280,000) in 1997, after a 10-month quiescence following a Ms 6.9 earthquake on 19 March 1996 in the same area. From 21 January 1997, through 18 October 1997, 15 earthquakes occurred with Ms ≥ 5.0, seven of which with Ms ≥ 6.0. Such sequences of strong earthquakes are rare around the world, but have occurred six times in the land area of China during this century. Of the 15 Ms ≥ 5.0 earthquakes in the Jiashi sequence, eight fell within the predicted 7-day time windows of a total of 8 short-term and imminent-stage predictions, but the initial shocks of the sequence (January 21, Ms 6.4, 6.3) were not predicted. Three of the eight predictions made were not fulfilled, one of which was announced to the public (a false alarm). Four of the remaining five predictions were acted on by local authorities and the public was notified 2.5 h to 4 days before the earthquakes, which caused no deaths. One earthquake (April 11, Ms 6.6) struck 30 min after the prediction was made but before action could be taken by the local authorities, and it caused nine deaths. These predictions were based on composite observations of precursory anomalies in seismicity, electromagnetic fields, and crustal deformation, which were in turn compiled over the past 30 years in a nationwide earthquake monitoring program. Examples of precursory anomalies include: (1) a clear seismicity pattern of “quiescence—intensification—main shock(s)” was observed for the April 6 earthquakes (Ms 6.3, 6.4), which was previously applied to the prediction of the well-known 1975 Haicheng earthquake in Laoning, China; (2) distinct decreases in b-values preceded the earthquakes on March 1 (Ms 6.0) and April 6 (Ms 6.3, 6.4); (3) anomalous variation of geomagnetic vertical component preceded the April 6 earthquakes (Ms 6.3, 6.4); (4) sudden decreases in borehole strain preceded 8 of the earthquakes.

Tidal calibration of borehole strain meters: Removing the effects of small‐scale inhomogeneity

We investigate the estimation of Earth strain from borehole strain meter data in a study of tidal calibration of the Gladwin borehole tensor strain meter (BTSM) at Piñon Flat. Small‐scale geological inhomogeneity is one of several effects examined that cross couple remote areal/shear strain into measured areal/shear strain. A methodology is developed for incorporating cross coupling into the strain meter calibration. Using the measured strain tides from the colocated laser strain meter (LSM) as a reference, we show that calibration of the BTSM with cross coupling removes systematic errors of up to 30% in the borehole strain meter tides. This calibration accurately relates the BTSM measurements to strains at the scale length of the LSM, about 1 km. The calibration technique provides a solution to a major criticism of all short‐baseline strain measurements, namely, that tectonic strains are not representatively sampled due to small‐scale inhomogeneities. The technique removes errors potentially greater than 50% in observed strain offsets from fault slip, permitting improved constraint of slip mechanisms. We show that current theoretical estimates of strain tides in the instrument locality are not yet of sufficient accuracy for cross‐coupled calibration. Comparison of theoretical tides with measurements from the LSM suggest that at least half of the error is in the ocean load tide estimates.

A5 Continuous Evolution of the Eruption of Izu-Oshima, November 1986,From Borehole Strain Data

A5 Continuous Evolution of the Eruption of Izu-Oshima, November 1986,From Borehole Strain Data

Statistical regression applied to borehole strain measurement data analysis: D. H. S. Zou, Geotechnical & Geological Engineering, 13(1), 1995, pp 17–27

Statistical regression applied to borehole strain measurement data analysis: D. H. S. Zou, Geotechnical & Geological Engineering, 13(1), 1995, pp 17–27

Statistical regression applied to borehole strain measurements data analysis

In mining and geotechnical engineering, it is usually necessary to carry out field measurements in order to obtain information. Parameters are often measured indirectly and calculated based on certain relationships to the measured quantities. More often, the number of measurements taken is greater than the minimum required, in order to increase the reliability of results. However, some data points are less reliable than others for reasons such as measurement errors; a solution which best fits the measurement data is obtained accordingly. As a result, there is a residual or a difference between the individual quantities measured and those predicted from the best-fit solution. This brings about a question of how big a residual is acceptable for a solution to be reliable. It is also important to know whether the data point with the largest residual is the most erroneous, whether those data points with large residuals should be deleted and how many of them should be deleted. Standard deviation may provide a measure of the data divergence but it is questionable if this parameter can be used as a measure of the reliability of solution. In order to solve these problems, the author has done extensive study in this area, especially as part of geotechnical data analysis. In this paper, the statistical multiple regression method is introduced to analyse the measurement data. The method is applied to the analysis ofin situ stress measurement and can be easily adopted to analyse data from other field measurements and laboratory tests. An example is included which illustrates the analysis procedure and shows the advantages of the method.

Continuous borehole strain in the San Andreas Fault zone before, during, and after the 28 June 1992, [formula omitted] 7.3 Landers, California, earthquake : M. J. S. Johnston, A. T. Linde & D. C. Agnew, Bulletin - Seismological Society of America, 84(3), 1994, pp 799–805

Continuous borehole strain in the San Andreas Fault zone before, during, and after the 28 June 1992, [formula omitted] 7.3 Landers, California, earthquake : M. J. S. Johnston, A. T. Linde & D. C. Agnew, Bulletin - Seismological Society of America, 84(3), 1994, pp 799–805

In situ stress determination using the under-excavation technique—I. Theory

The under-excavation technique (UET) is a unique in situ stress determination method which permits the stress state to be estimated on a rock mass scale. In method, stress predictions can be made several times, once for each increment of excavation face. The analysis is based on the minimization of the sum of the squares of the difference between the measured and predicted strain and displacement changes. Readings from both CSIRO, CSIR and other borehole strain cells, can be used in conjunction with displacement measurements from convergence gauges, extensometers, inclinometers and tiltmeters. In this paper, the theoretical foundation of the UET is detailed. A discussion of the potential advantages as well as shortcoming is also presented.

In situ stress determination using the under-excavation technique—II. Applications

In Part I of this paper, the theoretical foundation for the under-excavation technique (UET) was presented and it was shown how the in situ stress state could be determined from strain measurements using CSIRO, CSIR or other borehole strain cells in conjunction with displacement measurements from convergence gauges, extensometers, inclinometers and tiltmeters. In this paper, applications of the UET are presented. In the first example, the far field stress state is determined for the case of a vent raise. The second example is for the case of a drift, excavated by standard blasting techniques. The results presented in this report illustrate that although the UET has limitations, just as all other in situ stress measurement methods, it represents an attractive alternative stress measurement method. The UET has the distinct advantage of sufficient redundancy in the data to assess the accuracy of the stress predictions, without prior knowledge of the in situ stress state.

Continuous borehole strain in the San Andreas fault zone before, during, and after the 28 June 1992, MW 7.3 Landers, California, earthquake

Abstract High-precision strain was observed with a borehole dilational strainmeter in the Devil's Punchbowl during the 11:58 UT 28 June 1992 MW 7.3 Landers earthquake and the large Big Bear aftershock (MW 6.3). The strainmeter is installed at a depth of 176 m in the fault zone approximately midway between the surface traces of the San Andreas and Punchbowl faults and is about 100 km from the 85-km-long Landers rupture. We have questioned whether unusual amplified strains indicating precursive slip or high fault compliance occurred on the faults ruptured by the Landers earthquake, or in the San Andreas fault zone before and during the earthquake, whether static offsets for both the Landers and Big Bear earthquakes agree with expectation from geodetic and seismologic models of the ruptures and with observations from a nearby two-color geodimeter network, and whether postseismic behavior indicated continued slip on the Landers rupture or local triggered slip on the San Andreas. We show that the strain observed during the earthquake at this instrument shows no apparent amplification effects. There are no indications of precursive strain in these strain data due to either local slip on the San Andreas or precursive slip on the eventual Landers rupture. The observations are generally consistent with models of the earthquake in which fault geometry and slip have the same form as that determined by either inversion of the seismic data or inversion of geodetically determined ground displacements produced by the earthquake. Finally, there are some indications of minor postseismic behavior, particularly during the month following the earthquake.

Laboratory study of borehole breakouts in Cordova Cream: a case of shear failure mechanism

We subjected vertical boreholes drilled in cubical specimens of Cordova Cream to a 3-dimensional stress field, and increased one or both of the horizontal principal stresses until breakout failure occurred. Acoustic emission, borehole strain, and visual monitoring of the borehole wall during testing revealed four stages of breakout development: crack initiation, extension, breakout formation, and stabilization. Thin section analysis suggests that breakout formation in Cordova Cream is the result of shear failure mechanism. The relationships at breakout stabilization between the two horizontal principal stresses and between the span at the borehole wall and the least horizontal stress suggest a potentially simple method of estimating the far-field state of stress if ‘breakouted’ borehole geometry is accurately mapped.