Observation Of Crustal Deformation Research Articles

Temperature compensation of fiber optic unbalanced interferometers for high resolution static strain sensing

Accurate temperature compensation challenges the use of fiber optic unbalanced interferometers in static strain sensing. We propose a temperature compensation theory and scheme of unbalanced interferometers using sensing fibers with different temperature coefficients, aiming at resolving the temperature disturbance of optical fibers and achieving high strain resolution. For the first time, we comprehensively analyze the thermal response of interferometers due to different temperature coefficients, different thermal behaviors, and inconsistent temperature disturbances in the optical fiber arms. A sensing combination and a reference combination are designed. The sensing combination measures a strain and compensates for the temperature disturbance of the sensing arm, and the reference combination provides a reference to compensate for the temperature disturbance of the reference arm and frequency drift of the interferometer in the sensing combination. The proposed scheme can compensate for the temperature disturbances of interferometers in the sensing combination completely. To verify the theory and scheme, bend-insensitive single-mode fibers and Boron/Germanium co-doped fibers are used as sensing fibers in the experiment. The experimental results show that the temperature resolution of the sensing arm is about 3.43 × 10−4 °C, and the static strain resolution of the unbalanced interferometer within 24 h after temperature compensation is about 2.55 nε. The temperature-compensated strain resolution of ∼nε indicates that the proposed temperature compensation theory and scheme can be used in high-resolution, long-term, low-frequency, and static strain sensing, such as crustal deformation observation in geophysical applications.

Application of traditional manual measurements and remote sensing technologies in monitoring natural disasters

Natural disasters have occurred frequently worldwide. Some manual measurements and remote sensing technologies are widely believed to be effective and convenient in hazard monitoring. This study illustrates the causes and impacts of three natural disasters including floods, wildfires and earthquakes, and analyzes the application of traditional and remote sensing technologies in monitoring these natural disasters. In flood monitoring, traditional tools include meteorological and hydrological detection facilities and equipment could obtain rainfall and water level. Remote sensing technologies could extract water bodies and make disaster evaluation. In wildfire monitoring, traditional tools include the standard equipment of urban fire departments, portable pumps, tank trucks, and earth-moving equipment. Remote sensing technologies could be applied to fuel mapping and fire estimates. In earthquake monitoring, traditional tools include seismic measurement, crustal deformation observation, geomagnetic measurement, telluric observation, gravity observation, in-situ stress observation, and groundwater dynamic observation. Remote sensing technologies could help monitor through house images and thermal data. Remote sensing technologies bring natural disaster monitoring systems a great revolution, both in data acquisition and processing methods.

Reduction of non-tidal oceanographic fluctuations in ocean-bottom pressure records of DONET using principal component analysis to enhance transient tectonic detectability

Ocean bottom pressure-gauge (OBP) records play an essential role in seafloor geodesy. Oceanographic fluctuations in OBP data, however, pose as a significant noise source in seafloor transient crustal deformation observations, including slow slip events (SSEs), making it crucial to evaluate them quantitatively. To extract the significant fluctuation phenomena common to multiple observation networks, including oceanographic fluctuations and tectonic signals, we applied principal component analysis (PCA) to the 3-year Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) OBP time series for 40 stations during 2016–2019. PCA could separate several oceanographic signals based on the characteristics of their spatial distributions, although evident transient tectonic signals could not be confirmed from the observed pressure records during this observed period. The spatial distribution of the first four principal components (PCs) reflected the common component, inclined component along sea depth, longitude component, and parabola-like pattern, respectively. By subtracting each PC (in particular, PC-2 and PC-4) from the time series, we could significantly reduce the sea depth dependence of OBP records, which has been highlighted in several previous studies and is also evident in this region. We interpreted PCs 2–4 as the reflection of the strength and meandering of ocean geostrophic currents based on a comparison with the PC spatial distribution of the numerical oceanographic models. In addition, to evaluate the ability of PCA to separate transient tectonic signal from OBP time series, including oceanographic fluctuations, we conducted a synthetic ramp assuming an SSE by rectangular fault and then applied PCA. The assumed synthetic tectonic signal could be separated from the oceanographic signals and included in the principal component independently depending on its amplitude, suggesting that the spatial distribution of each PC would change if the amplitude of the synthetic signal were sufficiently large. We propose a transient event-detection method based on the spatial distribution difference of a specific PC with or without a tectonic signal. We used the normalized inner product (NIP) between these PCs as the indicator of their similarities. This method can detect transient tectonic signals more significantly than the moment-magnitude scale of 5.9 from OBP records.Graphical

Review on Low-Noise Broadband Fiber Optic Seismic Sensor and Its Applications

Fiber optic seismic sensors have important application prospects in the field of earthquake science research and underground structure detection, due to their strong adaptability in harsh environments such as deep wells, seabeds, and glaciers. It has always been one of the key problems to achieve ultra-low noise levels over a wide measurement frequency band for fiber optic seismic sensors. This article reviews two typical low-noise broadband fiber optic seismic sensing techniques, including narrow-linewidth laser frequency scanning and frequency locking sensing technique, laser interferometric phase interrogation technique. The principles are given. The measurement frequency band and noise level are tested and discussed. Recent progresses on crustal deformation observation, earthquake monitoring, water temperature solid tide detection and deep earth structure exploration based on fiber optic seismic sensors are introduced. Finally, the possible research trends are discussed.

Experimental verification of seafloor crustal deformation observations by UAV-based GNSS-A

The Global Navigation Satellite System-Acoustic ranging combination technique (GNSS-A) is the only geodetic observation method that can precisely detect absolute horizontal and vertical seafloor crustal deformations at the centimetre scale. GNSS-A has detected many geophysical phenomena and is expected to make great contributions to earthquake disaster prevention science and geodesy. However, current observation methods that use vessels and buoys suffer from high cost or poor real-time performance, which leads to low observation frequency and delays in obtaining and transmitting disaster prevention information. To overcome these problems, a new sea surface platform is needed. Here, we present an unmanned aerial vehicle (UAV) system developed for GNSS-A surveys capable of landing on the sea surface. Submetre-level seafloor positioning is achieved based on real-time single-frequency GNSS data acquired over an actual site. UAV-based GNSS-A allows high-frequency, near real-time deployment, and low-cost seafloor geodetic observations. This system could be deployed to acquire high-frequency observations with centimetre-scale accuracies when using dual-frequency GNSS.

Time-dependent decrease in fault strength in the 2011–2016 Ibaraki–Fukushima earthquake sequence

SUMMARY Two near-identical Mw 5.8 earthquakes in 2011 and 2016 ruptured the Mochiyama Fault in the Ibaraki–Fukushima region of Japan. The unusually short repeat time between the two earthquakes provides a rare opportunity to estimate the evolution of stress on a fault through an earthquake cycle, as the stress drop in the first earthquake provides a reference value from which we can infer variations through time in the stresses required to cause earthquake rupture. By combining observations of crustal deformation from GPS, InSAR and seismology with numerical models of stress transfer due to coseismic deformation and post-seismic relaxation, we demonstrate that the rupture area on the Mochiyama Fault could only have been reloaded by up to 50–80 per cent of the 2011 earthquake stress drop (3–10 MPa) between that event and the subsequent 2016 earthquake. Most of this reloading was caused by afterslip around the rupture area driven by stress changes from the 2011 Mochiyama and Tohoku-oki earthquakes. We therefore infer that the Mochiyama Fault became weaker in the intervening 6 yr, with at least a 1–5 MPa drop in the shear stresses needed to break the fault in earthquakes. The mechanism(s) that led to this weakening are unclear, but were associated with extensive aftershock seismicity that released a cumulative moment similar to the 2011 main shock. Temporal changes in fault strength may therefore play a role in modulating the timing of moderate-magnitude earthquakes.

Sensitive quantum tiltmeter with nanoradian resolution

Precision tilt measurements are becoming more and more important in fundamental research and crustal deformation observations. A quantum tiltmeter based on atom interferometry could be among the most stable tiltmeters in theory but is currently constrained by the low resolution. Here, we demonstrate an extremely sensitive quantum tiltmeter with the configuration of a Mach-Zehnder-type atom interferometer for precisely measuring the crustal deformation. The scheme of two pairs of Raman beams sharing one retroreflection mirror effectively increases the scale factor, making this quantum tiltmeter achieve a sensitivity of $40\phantom{\rule{0.28em}{0ex}}\mathrm{nrad}/{\mathrm{Hz}}^{1/2}$ and a resolution of 1.8 nrad within an integration time of 640 s for tilt measurements, which represents an improvement on the sensitivity by a factor of 32 comparing to previous work. The Earth tilt tide lasting for 63 h has been observed with high signal-to-noise ratio by our quantum tiltmeter, which paves the way to study the crustal deformation with a quantum sensor.

Progress of Continuous Observation of Crustal Deformation Since Start of National Research Program for Earthquake Prediction (1965) and Summary of Results Obtained by the Author and Coworkers

Progress of Continuous Observation of Crustal Deformation Since Start of National Research Program for Earthquake Prediction (1965) and Summary of Results Obtained by the Author and Coworkers

Sensitivity Analysis for Seafloor Geodetic Constraints on Coseismic Slip and Interseismic Slip-Deficit Distributions

Estimating the coseismic slip distribution and interseismic slip-deficit distribution play an important role in understanding the mechanism of massive earthquakes and predicting the resulting damage. It is useful to observe the crustal deformation not only in the land area, but also directly above the seismogenic zone. Therefore, improvements in terms of measurement precision and increase in the number of observation points have been proposed in various forms of seafloor observation. However, there is lack of research on the quantitative evaluation of the estimation accuracy in cases where new crustal deformation observation points are available or when the precision of the observation methods have been improved. On the other hand, the crustal structure models are improving and finite element analysis using these highly detailed crustal structure models is becoming possible. As such, there is the real possibility of performing an inverted slip estimation with high accuracy via numerical experiments. In view of this, in this study, we proposed a method for quantitatively evaluating the improvement in the estimation accuracy of the coseismic slip distribution and the interseismic slip-deficit distribution in cases where new crustal deformation observation points are available or where the precision of the observation methods have been improved. As a demonstration, a quantitative evaluation was performed using an actual crustal structure model and observation point arrangement. For the target area, we selected the Kuril Trench off Tokachi and Nemuro, where M9-class earthquakes have been known to occur in the past and where the next imminent earthquake is anticipated. To appropriately handle the effects of the topography and plate boundary geometry, a highly detailed three-dimensional finite element model was constructed and Green’s functions of crustal deformation were calculated with high accuracy. By performing many inversions via optimization using Green’s functions, we statistically evaluated the effect of increase in the number of observation points of the seafloor crustal deformation measurement and the influence of measurement error, taking into consideration the diversity of measurement errors. As a result, it was demonstrated that the observation of seafloor crustal deformation near the trench axis plays an extremely important role in the estimation performance.

Estimation of fault models for short-term slow\xa0slip events from groundwater pressure in soft sedimentary layers

Deep low-frequency tremors and short-term slow slip events (SSEs) are known to occur along the Nankai Trough in Japan. Although short-term SSEs are thought to occur repeatedly in the northern part of Ise Bay, deep low-frequency tremors are not observed there. Because the area around the northern part of Ise Bay is characterized by soft sedimentary layers not suitable for strainmeter or tiltmeter installation, there are no high-quality crustal deformation observation sites in the area. Accordingly, the local extent of slip of short-term SSEs has not been confirmed. We significantly improved the crustal strain sensitivity of the groundwater level (pressure) in the inner pipe of the observation well at the Hokusei observation site (HKSi, northwest of Ise Bay) by sealing it with a packer. Consequently, we were able to observe groundwater pressure changes related to slow slip at the plate boundary. We estimate that slip of short-term SSEs during July 2016, November 2017, and April 2018 extended to the northern part of Ise Bay. Furthermore, groundwater pressure fluctuations at HKSi in April 2018 greatly improved the SSE fault model, confirming that slow slip occurs in the area, despite the absence of deep low-frequency tremor. The slips without tremors are a characteristic of the northern area of Ise Bay, differing from other areas of the Nankai Trough. Our results demonstrate that groundwater level/pressure fluctuations are a powerful tool for crustal deformation observations in areas characterized by soft sedimentary layers.

Kinematics of Fault Slip Associated with the 4–6 July 2019 Ridgecrest, California, Earthquake Sequence

ABSTRACT The 2019 Ridgecrest, California, earthquake sequence produced observable crustal deformation over much of central and southern California, as well as surface rupture over several tens of kilometers. To obtain a detailed picture of the fault slip involved in the 4 July M 6.4 foreshock and 6 July M 7.1 mainshock, we combine strong-motion seismic waveforms with crustal deformation observations to obtain kinematic and static slip models of both events. We sample the regional seismic wavefield for both the foreshock and mainshock with three-component records from 31 stations of the California Integrated Seismic Network. The deformation observations include Global Positioning System (GPS), Interferometric Synthetic Aperture Radar (InSAR), and borehole strainmeter recordings of the dynamic strain field. These data collectively constrain the kinematic coseismic slip distributions of the events, with measurements variously observing coseismic slip from one event (e.g., seismic waveforms, kinematic solutions from continuous GPS, and strainmeter time series) or coseismic slip from both events combined (InSAR). We find that the foreshock ruptured two separate faults, one with left-lateral strike slip on a northeast–southwest-trending fault and the other with right-lateral strike slip on an orthogonal fault, with unilateral rupture propagation along both. The mainshock ruptured a series of northwest–southeast-trending faults with right-lateral strike slip concentrated in the uppermost 6 km with exceptionally low-rupture velocity averaging 1.0–1.5 km/s. A possible explanation for the low-rupture velocity is that the mainshock rupture expended relatively high energy, generating secondary fractures in off-fault deformation, which is consistent with field and seismic evidence of plastic deformation on small fault strands adjacent to the main rupture trace.

P76 安達太良山沼ノ平火口の地殻変動及び全磁力の繰り返し観測 1997-2002 年

P76 安達太良山沼ノ平火口の地殻変動及び全磁力の繰り返し観測 1997-2002 年

InSAR and GPS measurements of crustal deformation due to seasonal loading of Tehri reservoir in Garhwal Himalaya, India

Author(s): Gahalaut, VK; Yadav, RK; Sreejith, KM; Gahalaut, K; Burgmann, R; Agrawa, R; Sati, SP; Bansal, A | Abstract: We report unique observations of crustal deformation caused by the seasonal water level changes of Tehri reservoir in the Garhwal region ofNWHimalaya from GPS measurements and Interferometric Synthetic Aperture Radar (InSAR) analysis. All GPS sites along the Himalaya are strongly influenced by seasonal hydrological and atmospheric loading. However, the GPS siteKUNRlocated near the reservoir additionally exhibits anomalous variations due to seasonal water loading and unloading by the reservoir. Our InSAR analysis confirms that the seasonal filling of the reservoir causes measurable subsidence in its neighbourhood. In addition to the elastic deformation caused by the seasonal reservoir loading and the negligible poroelastic deformation caused by associated fluid pressure changes, there is an unaccounted biannual deformation in the east component of the GPS time-series which we suspect to be caused by altered hydrological conditions due to the reservoir operations. Understanding crustal deformation processes due to such anthropogenic sources helps in separating deformation caused by tectonic, hydrological and atmospheric effects from that caused by these activities.

Ultrahigh resolution fiber optic strain sensing system for crustal deformation observation

Due to the advantages of high resolution, low cost, small size, easy deployment and capability of multiplexed sensing, the recent developed optical fiber grating sensors provide powerful tools for crustal deformation monitoring. This paper reviews the development of several types of fiber-optic sensors with ultrahigh resolution in quasi-static domain. The fiber Bragg grating based Fabry-Perot interferometers and the -phase-shifted fiber Bragg gratings which are used as sensing components in the high resolution sensors are introduced. Some novel techniques such as interrogating the sensing components with intensity modulation sideband, dual feedback-loop structure for high bandwidth/large measurement range sensing, and the time-domain multiplexing of the high resolution quasi-static strain sensor are discussed in detail. Each sensing scheme with both operation process and achieved performances are given. The implementation of fiber grating sensors for in-situ measurement of crustal deformation and the results are also introduced. Compared with the traditional methods used in crustal deformation observation, the high-performance fiber optic strain sensors mentioned in the paper shows great potentials in providing wider measurement approaches in geophysical researches.

On the mechanisms governing dike arrest: Insight from the 2000 Miyakejima dike injection

Magma stored beneath volcanoes is sometimes transported out of the magma chambers by means of laterally propagating dikes, which can lead to fissure eruptions if they intersect the Earth's surface. The driving force for lateral dike propagation can be a lateral tectonic stress gradient, the stress gradient due to the topographic loads, the overpressure of the magma chamber, or a combination of those forces.The 2000 dike intrusion at Miyakejima volcano, Izu arc, Japan, propagated laterally for about 30 km and stopped in correspondence of a strike-slip system, sub-perpendicular to the dike plane. Then the dike continued to inflate, without further propagation. Abundant seismicity was produced, including five M>6 earthquakes, one of which occurred on the pre-existing fault system close to the tip of the dike, at approximately the time of arrest. It has been proposed that the main cause for the dike arrest was the fault-induced stress.Here we use a boundary element numerical approach to study the interplay between a propagating dike and a pre-stressed strike-slip fault and check the relative role played by dike–fault interaction and topographic loading in arresting the Miyakejima dike. We calibrate the model parameters according to previous estimates of dike opening and fault displacement based on crustal deformation observations. By computing the energy released during the propagation, our model indicates whether the dike will stop at a given location. We find that the stress gradient induced by the topography is needed for an opening distribution along the dike consistent with the observed seismicity, but it cannot explain its arrest at the prescribed location. On the other hand, the interaction of dike with the fault explains the arrest but not the opening distribution. The joint effect of the topographic load and the stress interaction with strike-slip fault is consistent with the observations, provided the pre-existing fault system is pre-loaded with a significant stress, released gradually during the dike–fault interplay.Our results reveal how the mechanical interaction between dikes and faults may affect the propagation of magmatic intrusions in general. This has implications for our understanding of the geometrical arrangement of rift segments and transform faults in Mid Ocean Ridges, and for the interplay between dikes and dike-induced graben systems.

Potential for a large earthquake near Los Angeles inferred from the 2014 La Habra earthquake.

Tectonic motion across the Los Angeles region is distributed across an intricate network of strike‐slip and thrust faults that will be released in destructive earthquakes similar to or larger than the 1933 M6.4 Long Beach and 1994 M6.7 Northridge events. Here we show that Los Angeles regional thrust, strike‐slip, and oblique faults are connected and move concurrently with measurable surface deformation, even in moderate magnitude earthquakes, as part of a fault system that accommodates north‐south shortening and westerly tectonic escape of northern Los Angeles. The 28 March 2014 M5.1 La Habra earthquake occurred on a northeast striking, northwest dipping left‐lateral oblique thrust fault northeast of Los Angeles. We present crustal deformation observation spanning the earthquake showing that concurrent deformation occurred on several structures in the shallow crust. The seismic moment of the earthquake is 82% of the total geodetic moment released. Slip within the unconsolidated upper sedimentary layer may reflect shallow release of accumulated strain on still‐locked deeper structures. A future M6.1–6.3 earthquake would account for the accumulated strain. Such an event could occur on any one or several of these faults, which may not have been identified by geologic surface mapping.

GPS Observations of Crustal Deformation Associated with the 2012 Mw 7.8 Haida Gwaii Earthquake

Abstract On 28 October 2012, an M w 7.8 earthquake occurred off the west coast of Haida Gwaii, British Columbia. Although past large events at this margin reflect strike‐slip motion between the Pacific and North American plates (e.g., 1949 M s 8.1), this earthquake involved low‐angle thrust faulting with a slip direction almost perpendicular to the margin, a consequence of slip partitioning at this obliquely convergent margin. To refine regional source models, we investigated the coseismic and postseismic displacements using a network of Global Positioning System (GPS) sites. Coseismic movement at the campaign site closest to the coast and about 30 km from the epicenter is 115 cm to the south‐southwest, with 30 cm of subsidence. The only continuously recording GPS station on Haida Gwaii at the time of the earthquake, about 80 km from the epicenter, provides a robust coseismic displacement estimate of 22 cm to the south‐southwest. The coseismic results are consistent with a shallow‐dipping thrust rupture underlying the Queen Charlotte terrace, immediately seaward of the Queen Charlotte fault. These results allowed us to update rupture models that were originally derived from seismic waveforms and tsunami data. Estimates of cumulative postseismic horizontal displacements over about one year from seven sites are up to 6 cm, with a systematic along‐strike variation in azimuth from south‐southwest to southeast from north to south in the study area. Besides viscoelastic stress relaxation, these postseismic trends may indicate afterslip on the deeper plate interface beneath northern Moresby Island and possibly aseismic slip along the Queen Charlotte or subparallel faults offshore of southern Moresby Island. Online Material: Figures of three‐component daily position estimates from Bernese analysis at Global Positioning System tracking stations on Haida Gwaii and the adjacent mainland.

The Ms7.0 Lushan earthquake and the activity of the Longmenshan fault zone

The M s7.0 Lushan earthquake is directly related to the activity of Longmenshan fault zone. In this article, deformation monitoring data in Longmenshan and its surrounding areas were analyzed and the result shows that the activity trend of Longmenshan fault zone depends on the relative motion between Bayan Har Block and Sichuan Basin, and the main power of the movement comes from the Tibetan Plateau and the upper Yangtze craton massif of push. In recent years, the Longmenshan and its surrounding areas is one of the main seismogenic area in mainland China. In this paper, combination with seismogenic area of geological structure and crustal deformation observation data analysis results, the relationship between the earthquake and Longmenshan fault zone activity was discussed, and the key monitoring areas in the next five years were proposed.

Is the Ryukyu subduction zone in Japan coupled or decoupled? —The necessity of seafloor crustal deformation observation

Abstract The 2004 Sumatra-Andaman earthquake of M w 9.3 occurred in a region where a giant earthquake seemed unlikely from the point of view of tectonics. This clearly implies that our current understanding of strain accumulation processes of large earthquakes at subduction zones needs to be reexamined. The Ryukyu subduction zone is one such zone since no large earthquake has been anticipated there for reasons similar those pertaining to the Sumatra-Andaman arc. Based on our analysis of historical earthquakes, plate motion, back-arc spreading, and GPS observation along the Ryukyu trench, we highly recommend monitoring seafloor crustal deformation along this trench to clarify whether a large earthquake (M w>8) could potentially occur there in the future.

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

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