Carl Kisslinger

Processes during the Matsushiro, Japan, Earthquake Swarm as Revealed by Leveling, Gravity, and Spring-Flow Observations

Recently revised leveling data and a more complete set of gravity data show that the uplift accompanying the later part of the Matsushiro swarm in central Honshu can be explained as due to dilatant expansion of the source region during the formation of a new fault. The local dilatancy occurred between the second and third peaks of seismic activity, although some preswarm dilatancy may have taken place in the region. It is likely that water inflow kept the medium saturated during expansion, except possibly for the times of most rapid uplift, when the drop in seismic activity indicates dilatancy hardening. A reasonable amount of horizontal expansion can explain the observed rate of change of gravity during uplift. The gravity measurements carry uncertainties of the same order as the observed changes, but the ensemble of data indicates clear trends during uplift and subsidence. The volume of land subsidence following the peak uplift agrees very closely with the best estimates of anomalous outflow of warm mineral water from springs during the last part of the swarm and supports the conclusion that subsidence was due to closing of water-filled cracks. The local rate of change of gravity during subsidence is very high, 1 mgal/m, and can only partly be accounted for by density increase due to crack closure.

A review of theories of mechanisms of induced seismicity

Abstract Theories of the physical processes leading to the stimulation of seismic activity by underground explosions, fluid injection, and reservoir impoundment are summarized. In all cases, the materials must be pre-stressed to a substantial fraction of their breaking strength in order for seismicity to be induced. Stress concentrations due to the presence of old faults or to inhomogeneities in the material properties play an important role in localizing induced seismicity. For the few cases for which data are available, the stimulation of earthquakes by fluid injection in bore holes is adequately explained by a Coulomb-Mohr failure criterion and the concept of effective pressure in a water-filled porous mechanism. Reservoir-related earthquakes are most likely due to the same mechanism, but, in view of the low injection pressures, additional physical or chemical effects of the water on the materials may play an important role. There may be a weakening of the materials in old fault zones by the introduction of water or static fatigue in silicate rocks due to stress corrosion.

Seismotectonics of intermediate-depth earthquakes from properties of aftershock sequences

Abstract Aftershock sequences following two intermediate-depth earthquakes have been analyzed to determine their spatial and temporal distributions. The Kanaga Pass earthquake ( M b = 6.0) occurred at 105 km depth in the central Aleutian Islands. Data were provided by the Central Aleutians Seismic Network. The Iwaizumi Town earthquake ( m b = 6.4) occurred at 75 km depth, under northern Honshu, Japan. Data were provided by the network of Tohoku University. For both events the hypocenter distribution of the aftershocks agreed well with focal mechanism solutions derived by others, with down-dip compression for both. Both events were followed by numerous aftershocks that decayed with time initially according to the modified Omori relation, with p -value close to 1. In both cases, activity at a higher rate than that expected from the Omori relation began after several months, without a strong aftershock to trigger it. The Kanaga Pass activity is modeled by two Omori sequences, the second beginning 64 days after the mainshock. The p -values are 0.92 and 1.04, respectively. The corresponding b -values are 1.01 and 1.03. The Iwaizumi Town sequence is modeled by a single Omori sequence, p = 0.96, plus a constant rate of activity, 0.25 events/day, for 63 days, beginning 120.5 days after the mainshock. The b -value of the main sequence was 0.91 ± 0.14, up to the start of the linear surge, for which the b -value was 1.23 ± 0.47. No strong aftershock or event in the vicinity of the aftershock zone occurred to trigger the secondary activity, in either case. The cause of the secondary activity is not known. The two sequences occurred in subduction zones with similar properties, and in both cases previous seismicity shows a deficiency of strong earthquakes in the main thrust zone above the aftershock source volumes. A strong creep event, or silent earthquake, in a weakly-coupled interplate contact zone is a plausible explanation for the secondary sequences. The unusual setting of the Iwaizumi event, at the bottom of the upper plane of the double-planed Wadati-Benioff zone under Honshu, may play a role in that case.

Aftershocks of the Andreanof Islands Earthquake of June 10, 1996, and local seismotectonics

Three questions have been addressed in connection with an Mw = 7.7 earthquake that occurred in the Andreanof Islands, Alaska, on June 10, 1996. First, was there any variation in seismic activity rate during the previous five years that might have been diagnostic of the imminent occurrence of this event? The answer, based on the USGS PDE catalog, is “No.” Second, though there were abundant pre-event earthquakes and aftershocks on both sides of Adak Canyon, why was there very little activity under the canyon itself, a property that has been observed previously?. It is not possible to resolve the cause of the behavior with existing seismological data. Finally, how does one explain the eastern group of aftershocks, which fell within the zone of abundant aftershocks of the 1986 Mw = 8 Andreanof Islands earthquake, when very little of the 1996 mainshock moment was released under or to the east of Adak Canyon? One explanation of these aftershocks is that the recent aftershocks are late aftershocks of 1986 whose occurrence within a short time was induced by the stress pulse, but not seismic slip, from the 1996 earthquake. Though large earthquakes in the Aleutians occur in distinct tectonic blocks, the boundaries of these blocks may not always be defined reliably by aftershock zones.

Time to reorganize federal Earth system science and technology

My usual reaction to plans to reorganize activities in the federal government is that these are the last resort of a bureaucrat who is faced with a tough problem and has no idea how to solve it. However, this may be the time to consider seriously a reorganization that would assemble key elements of Earth-oriented science and technology into a single federal agency. This is not a new idea, as proposals to achieve this goal have been formulated in the past and wiring diagrams for a new agency have been developed. These proposals have faded away in the face of resistance to substantial structural change that characterizes the federal bureaucracy.

A test of the semyenov prediction technique in the central Aleutian Islands

Abstract The earthquake-prediction technique based on systematic temporal variations in the ratio of the two body-wave velocities has been tested for selected events in the central Aleutian Islands. The goal was to determine if the phenomenon occurs for earthquakes in an active island arc. Two groups of earthquakes were selected, each in a concentrated source volume and well-placed with respect to the available local seismograph network, one relatively shallow (20 km) and the other along the thrust zone (about 45 km deep). Observational difficulties inherent to an island arc, namely the depth of the hypocenters, the high noise levels, and the complex geology, limit the number of events available for analysis and cause considerable scatter in the data. Nevertheless, a positive result, in which the velocity ratio decreased by about 5%, was obtained for at least one event in the shallow group for which there were sufficient preceding events to establish a definite trend. No premonitory changes were seen for the deeper source volume. A simple extension of the theory of the Wadati diagram permits an estimate of the velocity ratio in the overlying layers as well as in the source medium. The data indicate that under Amchitka Island, the velocity ratio is 1.82 (Poissons ratio 0.28) in the upper 10 km and 1.71–1.72 (Poissons ratio 0.24) from 10 km to at least 45 km.

That “Dahm” layer comments on renaming the D”

Benjamin F. Chao has suggested that Bullens layer just above the mantle-core boundary be renamed the Bullen layer. I believe that this is inappropriate. Boundaries and layers in the Earth are most properly named after their discoverers or those who first measured their location or properties. Cornelius G. Dahm [1936] first described this layer and deserves to have it named after him. This is appropriate also because it is convenient to have a short, easy-to-remember name that is similar to D″, which has been in use for a long time.

U.S.‐Japan Quake Prediction Research

For the seventh time since 1964, a seminar on earthquake prediction has been convened under the U.S.-Japan Cooperation in Science Program. The purpose of the seminar was to provide an opportunity for researchers from the two countries to share recent progress and future plans in the continuing effort to develop the scientific basis for predicting earthquakes and practical means for implementing prediction technology as it emerges. Thirty-six contributors, 15 from Japan and 21 from the U.S., met in Morro Bay, Calif.September 12–14. The following day they traveled to nearby sections of the San Andreas fault, including the site of the Parkfield prediction experiment. The conveners of the seminar were Hiroo Kanamori, Seismological Laboratory, California Institute of Technology (Caltech), for the U.S., and Takeshi Mikumo, Disaster Prevention Research Institute, Kyoto University, for Japan. Funding for the participants came from the U.S. National Science Foundation and the Japan Society for the Promotion of Science, supplemented by other agencies in both countries.

79.1 General introduction

This chapter comprises summaries extracted and excerpted from the National and Institutional Reports submitted by those nations and research entities that chose to prepare one. A few recently independent nations that are not now formally affiliated with IUGG and IASPEI, but were formerly part of a Member Country, did contribute reports, for which the editors have been grateful. These summaries are edited and prepared in final form to achieve uniformity of style and format. The revised versions are sent to the original authors for approval. Some editing is done to provide consistency in transliterating into the Latin alphabet from other alphabets or writing systems. These summaries are the products of much thoughtful effort by the authors, often teams of cooperating scientists within the nation. Practical limitations on the size of a printed volume require that we offer only capsule versions as guides to important stories of science in progress. The complete national and institutional reports, with figures, maps, tables, bibliographies, and biographies of key scientists, as well as some attached materials, such as earthquake catalogs and historically important documents, constitute a volume much greater than the printed Handbook.