Matsushiro Earthquake Research Articles

17. 水噴火としてみた松代地震(日本火山学会 1971 年度秋季大会講演要旨)

17. 水噴火としてみた松代地震(日本火山学会 1971 年度秋季大会講演要旨)

Causal mechanisms of seismo-EM phenomena during the 1965\u20131967 Matsushiro earthquake swarm

The 1965–1967 Matsushiro earthquake swarm in central Japan exhibited two unique characteristics. The first was a hydro-mechanical crust rupture resulting from degassing, volume expansion of CO2/water, and a crack opening within the critically stressed crust under a strike-slip stress. The other was, despite the lower total seismic energy, the occurrence of complexed seismo-electromagnetic (seismo-EM) phenomena of the geomagnetic intensity increase, unusual earthquake lights (EQLs) and atmospheric electric field (AEF) variations. Although the basic rupture process of this swarm of earthquakes is reasonably understood in terms of hydro-mechanical crust rupture, the associated seismo-EM processes remain largely unexplained. Here, we describe a series of seismo-EM mechanisms involved in the hydro-mechanical rupture process, as observed by coupling the electric interaction of rock rupture with CO2 gas and the dielectric-barrier discharge of the modelled fields in laboratory experiments. We found that CO2 gases passing through the newly created fracture surface of the rock were electrified to generate pressure-impressed current/electric dipoles, which could induce a magnetic field following Biot-Savart’s law, decrease the atmospheric electric field and generate dielectric-barrier discharge lightning affected by the coupling effect between the seismic and meteorological activities.

松代群発地震の初期発展過程

Matsushiro earthquake swarm is a most well known and well studied earthquake swarm in the history of seismology. From viewpoints of geophysics, geology and geochemistry, various observations, field surveys and analyses had been made to reveal characteristics of the swarm. On the basis of these studies, several models had been proposed to explain why and how the swarm originated and developed. However, majority of studies had focused on the activity around the climatic stage of the swarm in 1966 and so far, studies on the initial stage of the swarm in mid 1965 had remained few due to lack of sufficient observation data. The exact area where the swarm was born had not been known and the swarm was vaguely believed to originate from the area around Mt. Minakami in former Matsushiro town (now belongs to Nagano city). Considering that the manner of initial development of swarm activity represents an important characteristic of the swarm earthquake, we tried to get more clear view about initial stage of the swarm activity in this study. We re-investigated seismograms obtained by routine observation and studied seismograms of temporal stations for the first time which had not been processed yet. By scanning analogue seismograms, we made a complete data set of S-P times with high precision for each station. Although the data set of S-P times from two stations are not sufficient for conventional hypocenter location, we were able to narrow down a possible source area of the swarm activity under the reasonable assumptions. By considering direction of initial motion of P waves and assuming local velocity model of the upper crust in the region and plausible focal depth of 4.5km of the swarm earthquake, we found that the area of swarm in the very beginning in August, 1965 is located about 4km north-east of the Matsushiro earthquake fault (MEF) in former Wakaho town near its border with former Matsushiro town. Size of the initial swarm area was 3-4km in diameter. While swarm activity in the initial region was gradually decaying in September new swarm activity appeared separately from the initial swarm area around southern and south-west part of the MEF. Activity in the new swarm area had been increasing and it was developed to more intense swarm after October, 1965 when establishment of temporal seismic station network of the Earthquake Research Institute, University of Tokyo enabled detailed hypocenter location. The new swarm area coincides with the area where large amount of ground water moved upward and was released on the ground surface in the climatic stage of the swarm. It was well known that source area of the swarm was split and expanded toward north-east and south-west after March, 1967 in its climatic stage. Present study on the initial development of swarm area suggested that characteristics of the Matsushiro earthquake swarm such as splitting and expansion of its source area toward northeast and southwest were inherent in their early stage of the activity in August and September, 1965.

Oil the possible relationship between the Matsushiro earthquake swarm and the inactivity of Asama-yama Volcano

During the famous Matsushiro earthquake swarm more t h a n 700 000 (volcanic) earthquakes were observed. At (he same time remarkable contortion of the ground also took place together with other strange geophysical phenomena. In the course of these events, volcano Asama-yama (one of the most active volcanoes of the world) showed a perfect inactivity. This volcano is situated at a distance of about 30 km measured from Matsushiro, that is very near the site of the events. In the paper a causal relationship is suggested between the geophysical phenomena at .Matsushiro and the inactivity of Asama-yama. Two alternative possibilites are t r e a t e d briefly. The hypothetical character of these ideas is strongly emphasized by the author, however both possibilities appear to be physically real and can explain all the important geophysical events observed on the spot.

Status of the TOUGH-FLAC simulator and recent applications related to coupled fluid flow and crustal deformations

This paper presents recent advancement in and applications of TOUGH-FLAC, a simulator for multiphase fluid flow and geomechanics. The TOUGH-FLAC simulator links the TOUGH family multiphase fluid and heat transport codes with the commercial FLAC 3D geomechanical simulator. The most significant new TOUGH-FLAC development in the past few years is a revised architecture, enabling a more rigorous and tight coupling procedure with improved computational efficiency. The applications presented in this paper are related to modeling of crustal deformations caused by deep underground fluid movements and pressure changes as a result of both industrial activities (the In Salah CO 2 Storage Project and the Geysers Geothermal Field) and natural events (the 1960s Matsushiro Earthquake Swarm). Finally, the paper provides some perspectives on the future of TOUGH-FLAC in light of its applicability to practical problems and the need for high-performance computing capabilities for field-scale problems, such as industrial-scale CO 2 storage and enhanced geothermal systems. It is concluded that despite some limitations to fully adapting a commercial code such as FLAC 3D for some specialized research and computational needs, TOUGH-FLAC is likely to remain a pragmatic simulation approach, with an increasing number of users in both academia and industry.

Modeling crustal deformation and rupture processes related to upwelling of deep CO2‐rich fluids during the 1965–1967 Matsushiro earthquake swarm in Japan

In Matsushiro, central Japan, a series of more than 700,000 earthquakes occurred over a 2‐year period (1965–1967) associated with a strike‐slip faulting sequence. This swarm of earthquakes resulted in ground surface deformations, cracking of the topsoil, and enhanced spring outflows with changes in chemical compositions, as well as carbon dioxide (CO2) degassing. Previous investigations of the Matsushiro earthquake swarm have suggested that migration of underground water and/or magma may have had a strong influence on the swarm activity. In this study, employing coupled multiphase flow and geomechanical modeling, we show that observed crustal deformations and seismicity could have been driven by upwelling of deep CO2‐rich fluids around the intersection of two fault zones: the regional east Nagano earthquake fault and the conjugate Matsushiro fault. We show that the observed spatial evolution of seismicity along the two faults and magnitudes surface uplift are convincingly explained by a few megapascals of pressurization from the upwelling fluid within the critically stressed crust, a crust under a strike‐slip stress regime near the frictional strength limit. Our analysis indicates that the most important cause for triggering of seismicity during the Matsushiro swarm was the fluid pressurization with the associated reduction in effective stress and strength in fault segments that were initially near critically stressed for shear failure. Moreover, our analysis indicates that a 2‐order‐of‐magnitude permeability enhancement in ruptured fault segments may be necessary to match the observed time evolution of surface uplift. We conclude that our hydromechanical modeling study of the Matsushiro earthquake swarm shows a clear connection between earthquake rupture, deformation, stress, and permeability changes, as well as large‐scale fluid flow related to degassing of CO2 in the shallow seismogenic crust. Thus our study provides further evidence of the important role of deep fluid sources in earthquake fault dynamics and surface deformations.

Hydrogeochemical Modeling for Natural Analogue Study of CO2 Leakage due to Matsushiro Earthquake Swarm

Abstract For natural analogue study of CO2 leakage, the Matsushiro field in central Japan was selected to investigate hydrogeochemical behavior due to CO2 leakage from a fault zone during the period of the Matsushiro Earthquake Swarm between 1965 and 1967. One of the main objectives of the modeling study is to understand effects of hydrogeological characteristics of shallow aquifers and seal mechanism due to mineral precipitation in a fault zone. Reactive geochemical transport simulations were carried out using TOUGHREACT. Based on the historical data including discharge rate, chemical composition of water and seismic activity, we developed a numerical model to reproduce the geochemical behavior during and after the swarm earthquakes. A two-dimensional model (2000 m×1800 m) for the fault zone using the Multiple Interacting Continua (MINC) method was set up to evaluate geochemical effects during degassing and mixing of brine upwelling along the fault zone. The simulation results can capture the observed trend at the Matsushiro field. Supercritical and gaseous CO2 occur in the deep and the shallow fracture zones, respectively. During the earthquake swarm, CO2 saturated brine moves up along the fracture zone and CO2 degassing occurs in the shallow zone. Subsequently, water pH increases and a small amount of calcite precipitates. Lateral groundwater flow in shallow aquifers, which transports the CO2 away from the fault zone, makes CO2 surface discharge small. At the same time, calcite dissolves after the swarm due to lateral fresh water recharge. The result is consistent with the fact that no calcite observed in the core from the 80 m borehole drilled during the course of this study, indicating that CO2 discharge is likely affected by lateral shallow groundwater flow. Measurements of surface CO2 flux and soil gas δ 13 C indicated that little seepage of CO2 occurs in the area of the fan deposits at present, 40 years after the earthquake swarm. Using the same model, long term leakage simulations (if supercritical CO2 leaked along fault zone from the storage reservoir) were carried out to test whether CO2 surface leakage occurs or not. Two simulations were performed, with CO2 upflow rates of 50,000 and 100,000 kg/year in an area of 25 m×25 m. CO2 surface leakage does not occur in the first case, while CO2 leakage occurs in the second case. CO2 surface leakage is reduced because CO2 dissolves in groundwater flowing laterally in shallow aquifer. These simulations indicate that it is important to understand hydrogeological characteristics of aquifers underlain by reservoir as well as cap rocks.

A Point-process Analysis of the Matsushiro Earthquake Swarm Sequence: The Effect of Water on Earthquake Occurrence

Temporal characteristics of the famous Matsushiro earthquake swarm were investigated quantitatively using point-process analysis. Analysis of the earthquake occurrence rate revealed not only the precise and interesting process of the swarm, but also the relation between pore water pressure and the strength of the epidemic effect, and the modified Omori-type temporal decay of earthquake activity. The occurrence rate function λ(t) for this swarm is represented well as where f(t) represents the contribution of the swarm driver, which was the erupting water from the deep in this case, and the second term represents an epidemic effect of the modified Omori type. Based on changes in the form of f(t), this two-year long swarm was divided into six periods and one short transitional epoch. The form of f(t) in each period revealed the detail of the water erupting process. In the final stage, f (t) decayed according to the modified Omori-formula form, while it decayed exponentially in the brief respite of the water eruption in the fourth period. When an exponential decay of swarm activity is observed, we have to be cautious of a sudden restart of the violent activity. The epidemic effect is stronger when the pressure of the pore water is higher. Even when the pressure is not high, the p value in the epidemic effect is small, when there is plenty of pore water. However, the epidemic effect produced about a quarter of the earthquakes even though there was not much pore water in the rocks.

Hydrothermal system beneath Aso volcano as inferred from self-potential mapping and resistivity structure

We conducted self-potential (SP) surveys sequentially from part to part over the central cones of Aso volcano since August 1998 by December 2001. The compiled SP map revealed large SP anomalies on the central cones. The main feature of the SP map is a ‘W-shaped’ profile along the NS-transect over the central cones. It is probable that this characteristic SP profile is produced by the combination of hydrothermal upwelling in the middle and topographic effect. A positive anomaly showing a large concentric pattern has appeared after correcting the topographic effect. To evaluate this SP anomaly, we implemented a numerical code that calculates electric potential produced by arbitrarily positioned current sources and sinks in any three-dimensional resistivity structure. A layered structure obtained from a time-domain electromagnetic (TDEM) field experiment was used for the resistivity model. The estimated current source is 300 A, being located in a conductive layer around the sea level. Meanwhile, sinks were estimated to sit on a circular area corresponding to the marginal part of the conductive layer. Water and heat budget study gives a lower limit of water mass transfer from depth to the bottom of the crater lake of Nakadake. This value was used to estimate the equivalent current in either case of electro-kinetic (EK) [Mizutani, H., Ishido, T., 1976. A new interpretation of magnetic field variation associated with the Matsushiro earthquakes, J. Geomag. Geoelectr., 28, 179–188.] or rapid fluid disruption (RFD) process [Johnston, M.J.S., Byerlee, J.D., Lockner, D., 2001. Rapid fluid disruption: A source for self-potential anomalies on volcanoes, J. Geophys. Res. 106(B3), 4327-4335.]. This comparison suggests that the former process is preferable to explain the observed SP anomaly. From these results we infer a large-scale hydrothermal system beneath the central cones of Aso volcano, in which the fluid flow initiates from the surrounding area, converging to the central vent to transport the heat and materials up to the crater lake of Nakadake through a vapor-filled conduit.

同位体比から見た松代群発地震地域の深部流体の起源

同位体比から見た松代群発地震地域の深部流体の起源

松代群発地震地域に湧出する深層地下水

松代群発地震地域に湧出する深層地下水

Isotopic compositions of rare gases in the Matsushiro earthquake fault region.

Elemental and isotopic compositions of rare gases in gas samples from “Helium spots” and CO2-spring in the fault zone formed by the Matsushiro earthquake swarms, reported by WAKITA et al. (1978), have been analyzed mass spectrometrically. Isotopic compositions of rare gases were atmospheric except for 3He/4He and 40Ar/36Ar ratios. 3He/4He ratios were (9.12 ± 0.58) × 10-6 and (9.10±0.69) × 10-6, and 40Ar/34Ar ratios were 308 ± 9 and 304 ± 8 for “Helium spots” and CO2-spring, respectively. Rare gas elemental abundance patterns for both samples were similar to a pattern produced by the dissolution equilibrium of atmospheric rare gases in water. The origin of rare gases is discussed. The 3He/4He ratio found in the fault zone suggests that the systematic observation of 3He/4He ratio may be useful for the detection of precursory phenomena of an earthquake.

Theory of electrokinetic‐magnetic anomalies in a faulted half‐space

Fluid motion in the vicinity of a vertical fault separating regions of different streaming potential coefficient can produce an external magnetic field of observable magnitude. If tectonic stress changes along the fault produce fluid motion, the magnetic field changes would be indicative of stress changes, and might precede severe fault motion. The largest component of the magnetic field is oriented parallel to the strike of the fault. Magnetic field changes produced by this mechanism will have electric fields associated with them with similar time variation; this is in contrast to magnetic field changes produced by changes in susceptibility or remanent magnetization, which have no associated electric field. Experiments aimed at the detection of tectonomagnetic effects should include electric field sensors to help in determining the source of any observed variations. The hypothesis of Mizutani and Ishido (1976) that the magnetic field changes associated with the Matsushiro earthquake swarms were produced by electrokinetic currents seems reasonable.

震源域における応力場

震源域における応力場

New vertical geodesy

Vertical geodesy is undergoing a revolution because of two factors. First, new precise three-dimensional position measurement techniques used over very long distances and based on extraterrestrial reference systems provide a new class and precision of geometric data previously unavailable for geophysical investigations. Second, physical models in tectonic theory for large earthquakes predict crustal distortions that violate the conventional assumptions used to interpret gravity and leveling data. Leveling and geometric elevation measurements are not directly comparable because the interpretation of leveling data is density-model dependent. Estimates of pre-1971 San Fernando earthquake elevation changes based on leveling of about 10 cm may be as much as 3 cm, or 40%, too large. Pre-1964 Niigata earthquake leveling surveys, previously used as confirmation of the dilatancy model, do not require dilatancy as an explanation and easily allow an alternative model with a subsurface density increase. Gravity is also not a dependable estimator of elevation change. But a combination of gravity with either leveling, if the dimensions of the distorted body are known or small, or geometric elevation measurements is essential for the determination of crustal density and strain changes. The 1965–1967 Matsushiro earthquake swarm leveling and gravity data show a significant dilatant strain of 0.6–1.8×10−4 if the proper model dimensions are used. This dilatant strain would be adequate to cause the observed drop in Vp/Vs, even if the crust were initially saturated prior to distortion. The combination of gravity, leveling, and the new geometric elevation measurements provides a useful parameter, gravitational potential, for the inversion of subsurface density distributions. Use of this parameter, defined as the free-air elevation anomaly, is illustrated for a nearly compensated mountain root structure and shows that this technique holds significant promise for the study of large, deep structures in the crust and upper mantle.

A new interpretation of magnetic field variation associated with the Matsushiro earthquakes.

Local magnetic field variation observed during the Matsushiro earthquake swarm in central Honshu, Japan, is well correlated with the variation of spring-water outflow but not with that of the seismic activity. This indicates that the origin of the magnetic field variation is not the stress-induced piezomagnetic effect but may be the water-induced electrokinetic effect proposed by MIZUTANI et al. (1975). The electrokinetic effect combined with the observed amount of water discharge is found to give the correct magnitude and sign of the local magnetic field variation observed at the two stations in Matsushiro area.

松代群発地震前後における地震波速度変化について

松代群発地震前後における地震波速度変化について

Investigation of Gravity Change Associated with the Matsushiro Earthquake Swarm

Investigation of Gravity Change Associated with the Matsushiro Earthquake Swarm

Intrusive Origin of the Matsushiro Earthquake Swarm

Research Article| February 01, 1975 Intrusive Origin of the Matsushiro Earthquake Swarm William D. Stuart; William D. Stuart 1National Center for Earthquake Research, U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Malcolm J.S. Johnston Malcolm J.S. Johnston 1National Center for Earthquake Research, U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Geology (1975) 3 (2): 63–67. https://doi.org/10.1130/0091-7613(1975)3<63:IOOTME>2.0.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation William D. Stuart, Malcolm J.S. Johnston; Intrusive Origin of the Matsushiro Earthquake Swarm. Geology 1975;; 3 (2): 63–67. doi: https://doi.org/10.1130/0091-7613(1975)3<63:IOOTME>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Vertical and horizontal displacements, seismicity, and local magnetic field variations observed during and after the Matsushiro earthquake swarm in central Honshu, Japan, appear to be consistent with inflation of a shallow magma reservoir within a crust containing pre-existing horizontal shear stresses. Theoretical analysis shows that increased magma pressure accompanying intrusion causes a domal uplift and also reduces the pressure in adjacent rocks. Reduced pressure implies lower frictional forces on fault planes and therefore accounts for the observed diffuse seismicity and left-lateral faulting. The coseismic increase of local magnetic field intensity is in accord with the piezomagnetic effect expected during growth of a magma inclusion; the subsequent slow decrease of the field in the five years following the swarm is explained by thermal demagnetization of host rocks. Concurrent gravity changes, although comparable to estimated errors, and spring-water outflow fluctuations are compatible with both the intrusion and dilatancy fluid-flow hypotheses. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Seismic activity induced by water injection at Matsushiro, Japan.

City water, amounting 2883m3, was pumped into a well of 1800m deep at Matsushiro, central Japan. The pumping pressure was 50 to 14 bars, Several days after the start of the fluid injection, a series of microearthquakes commenced two to four kilometers away from the well. Detailed investigations of those earthquakes confirmed that the unusual seismic activity was triggered by the water injection. Most of the supplied water seems to have permeated through the Matsushiro earthquake fault. Intrinsic permeability of the fault zone was estimated as 0.01-0.1 darcy, which are reasonable values for fractured rocks.