Short-term Precursors Research Articles

A kind of information on short-term and imminent earthquake precursors—research on atmospheric electric field anomalies before earthquakes

The long-time practice of observational research on earthquake prediction has shown that the information on short-term and imminent earthquake precursors can hardly be detected, but it is very important for practical and effective earthquake prediction. The result of analysis and study in this paper has shown that the anomaly of quasi-static atmospheric electric field may be a kind of reliable information on short-term and imminent earthquake precursors. On such a basis, the 20 years’ continuous and reliable data of atmospheric electric field observed at the Baijiatuan seismic station are used to study the correlation between the anomalies in seismic activity and relative quiet periods bear on the occurrence of near earthquakes within 200 km range around Beijing after the Tangshan earthquake. The observational results recently reported before hand in written form and earthquakes that actually occurred in near field in corresponding time periods are compared and analyzed. The efficacy of these written prediction opinions about near earthquakes in the recent 10 years is tested. From the test results, the brilliant prospect that the anomaly of quasi-static atmospheric electric field may really become a reliable mark for making short-term and imminent earthquake predictions is discussed. Besides, as a preliminary step, some judgment indexes for predicting earthquakes by use of the observational data of atmospheric electric field before earthquakes are put forward. In the last part, it is pointed out that it would be possible to obtain more believable judgment indexes for determining the three elements of near earthquakes before greater earthquakes (M S≥5) only if a relatively reasonable station network (2–4 stations every 10 000 km2) is deployed and further investigation is made.

Unusual low-frequency volcanic seismic events with slowly decaying coda waves observed at Galeras and other volcanoes

Events with slowly decaying coda waves are observed in active andesitic volcanoes associated mainly with vulcanian-type eruptions or large gas emissions. However, these signals are also recorded in some quiescent volcanoes. These unusual signals are considered to be related to magmatic activity and generally occur beneath the active crater. The signals have been observed to be a short-term precursor (Galeras volcano, Colombia, 1992–1993; Asama-yama volcano, Japan, 1983), after eruption (Tokachi-dake volcano, Japan, 1989), during seismic swarms (Meakan-dake volcano, Japan, 1982) and during quiescence (Puracévolcano, Colombia, 1994–1995; Tarumai volcano, Japan, 1970–1971, 1975). Spectral analysis reveals common characteristics for this type of signal. The spectrum is characterized by one or several sharp frequency peaks. Fundamental frequencies are not affected by epicentral distance, azimuth or travel time, indicating a source effect. The damping coefficient for coda waves ranges from 0.002 to 0.02 and is related to large values of the Quality factor ( Q c) ranging from 250 to 25, respectively. These parameters may be the result of large amounts of gas bubbles in the magma body.

Changes of Strain before Earthquakes: The Possibility of Routine Monitoring of Both Long-Term and Short-Term Precursors.

Earthquakes are extraordinarily complicated phenomena and deterministic prediction of the magnitude, time and place of large earthquakes is likely to be intrinsically impossible. A more simple phenomenon, the build up of deformation which leads to the earthquake, can be monitored by the behaviour of seismic shear waves, and this offers a way of forecasting the proximity of large earthquakes. Recent results, including field observations of shear waves before earthquakes, laboratory experiments with stress cells, and theoretical modelling of microscale deformation, demonstrate that long-term precursory build-up of deformation can be monitored for some years before a large earthquake. There may even be the possibility of identifying short-term precursors a few hours or days before the earthquake. This paper suggests that reliable routine earthquake forecasting would require controlled seismic experiments between a specific pattern of deep wells.

Distinct developmental patterns of short-term and long-term functioning lymphoid and myeloid precursors defined by competitive limiting dilution analysis in vivo.

Functional abilities of individual marrow precursor cells were defined by competitive limiting dilution without enrichment, tissue culture, or induced marking, manipulations that might affect cell functions. We directly measured long-term repopulating abilities in limiting doses (0.25-1.0 x 10(5)) of genetically marked congenic marrow cells. These were mixed with a standard dose of 4 or 5 x 10(5) competitor marrow cells, which contained a predictable distribution of precursor cells and allowed quantitative assays. Percentages of donor type T and B lymphocytes, granulocytes, platelets, and erythrocytes were measured in recipient blood. Applying the maximum likelihood statistic, concentrations (per 10(5)) of precursors repopulating at least one lineage were: 4.7 and 6.0 after 6 wk, 1.6 and 2.7 after 14 to 15 wk, and 1.2 and 1.9 after 30 to 32 wk; concentrations repopulating at least three lineages were 2.3 and 3.4 after 6 wk, 0.9 and 1.7 after 14 to 15 wk, and 0.9 and 1.3 after 32 wk. Almost all precursors functioning after 14 wk repopulated all lineages. At 6 wk, similar levels of donor cells were produced in recipients of both short- and long-term precursors. However, after 14 to 32 wk, contributions by short-term precursors (about two-thirds of the precursors) dropped to zero, while contributions by long-term precursors (about one-quarter of the precursors) expanded severalfold. The latter permanently repopulated all lineages after 30 to 32 wk, functioning as the most primitive stem cells (PSC) in the immune and myeloid systems. Nearly all the variance in long-term repopulated recipients was explained using the Poisson distribution to calculate donor percentages in a model where each donor and competitor PSC contributed equally.

Initiation process of earthquakes and its implications for seismic hazard reduction strategy.

For the average citizen and the public, "earthquake prediction" means "short-term prediction," a prediction of a specific earthquake on a relatively short time scale. Such prediction must specify the time, place, and magnitude of the earthquake in question with sufficiently high reliability. For this type of prediction, one must rely on some short-term precursors. Examinations of strain changes just before large earthquakes suggest that consistent detection of such precursory strain changes cannot be expected. Other precursory phenomena such as foreshocks and nonseismological anomalies do not occur consistently either. Thus, reliable short-term prediction would be very difficult. Although short-term predictions with large uncertainties could be useful for some areas if their social and economic environments can tolerate false alarms, such predictions would be impractical for most modern industrialized cities. A strategy for effective seismic hazard reduction is to take full advantage of the recent technical advancements in seismology, computers, and communication. In highly industrialized communities, rapid earthquake information is critically important for emergency services agencies, utilities, communications, financial companies, and media to make quick reports and damage estimates and to determine where emergency response is most needed. Long-term forecast, or prognosis, of earthquakes is important for development of realistic building codes, retrofitting existing structures, and land-use planning, but the distinction between short-term and long-term predictions needs to be clearly communicated to the public to avoid misunderstanding.

Signs of potential renewal of eruptive activity at La Fossa (Vulcano, Aeolian Islands)

Since the end of the last magmatic eruption (1890), activity of La Fossa (southern Tyrrhenian Sea, Italy) has consisted of fumarolic emissions of fluctuating intensity. Fluids are discharged principally at two fumarolic fields located in the northern rim of the active crater and at the beach sited at its northern foot. Increased thermal, seismic and geochemical activity has been recorded since 1978, when an earthquake of M=5.5 occurred in the region. This paper combines available geophysical and geochemical information in order to develop a tentative interpretation of two episodes of apparent unrest which occurred in 1985 and 1987–1988, enhancing the risk of renewal of the eruptive activity. The 1985 unrest consisted essentially of a sharp build up of the internal pressure in the shallow hydrothermal system, which was induced by the injection of hot gases of magmatic origin. The crater fumaroles displayed significant increases in CO2 and other acid species, but their outlet temperature did not change. Conversely, the 1987–1988 episode was characterized by appreciable modifications at the crater fumaroles, with only secondary effects at the fumarole system of the beach. The sliding of part of the eastern flank of the La Fossa cone into the sea occurred on 20 April 1988, when the region was affected by crustal dilatation producing a seismic sequence of relatively high intensity. Both episodes of unrest were accompanied by increases of local microseismic activity, which affected the nothern sector of the island in 1985, and the southern one in 1988. Finally, a phase of appreciable areal contraction was detected in 1990, probably due to the effect of the cooling and crystallization of magma at relatively shallow depths, accompanying the increased thermal activity at the crater fumaroles. Regional tectonic stress seems to play an important role in the transition of the volcanic system from a phase of relative stability to a phase of apparent unrest, inducing the heating and the expansion of shallow hydrothermal fluids. Available information is insufficient to indicate whether or not the volcano is building towards the renewal of a magmatic eruption, and there is no evidence to hypothesize episodes of significant magma migration. The frequency of measurements of many parameters needs to be increased in order to learn more about the temporal relationships between geochemical and geophysical variations preceding and accompanying periods of increased thermal activity. This will probably be a valid tool for recognizing short-term precursors of a future eruption, reducing the risk of false alarms.

Ultra low frequency electromagnetic wave anomaly and its spectrum characteristics before earthquakes

Many observations and researches show that abundant and intense ultra low frequency (ULF) electromagnetic anomalies appeare before local earthquakes. In order to understand this phenomenon systematically, the transmission property and the formation of the seismic-electric dipole are discussed in this paper. The results show that the vertical component of the ULF electric anomaly before earthquake has the properties of better penetration, less disturbance and high signal-to-noise ratio. The signal can be easily extracted and received. The anomaly should be an important way to seek for reliable short-term and imminent earthquake precursors. After the spectrum analysis of the (ULF) electric field anomalies, we found that the periods of the anomaly related to local earthquakes are from a few minutes to a dozens minutes. There is a relation between the spectrum of the anomaly and the epicentral distance. The ULF electric field anomalies strongly rely on the orientation of the seismogenic zone. The percolation electric field anomaly and its spectrum amplitude do not have obvious relation with the size of local earthquakes.

Use of satellites to detect seismo-electromagnetic effects

The seismo-electromagnetic effects are the electric and magnetic perturbations caused by natural geophysical activity such as earthquakes and volcanic eruptions. They include: electromagnetic emissions in a large frequency range, perturbations of ionospheric layers, anomalies on the records of VLF transmitter signals, nightglow observations. The hypotheses concerning the electromagnetic wave emissions during earthquakes are: direct wave production by compression of rocks near the focal point, or electric discharges due to a redistribution of electric charges in the ground (piezoelectric or electrokinetic effects). Such phenomena are of great interest, because they start a few hours before the shock and can be considered as short-term precursors. However, not all earthquakes produce such perturbations. These phenomena were recorded at ground-based stations as well as on satellites. Ground campaigns, close to the epicenters, are a priori easier to manage, but on the other hand, satellite observations provide coverage over most of the active seismic zones of the Earth. Satellite observations are useful in places that usually have a low-level background noise. This paper presents in a first time a review of these phenomena, and of the various hypotheses put forward. The use of satellites for studying these events, and related problems are also discussed.

Seismic assessment of phreatic-explosion hazard at ?La Fossa? Volcano (Island of Vulcano, Italy)

Active volcanic areas are sometimes affected by phreatic eruptions, which are explosions due to the outbreak of a confined pocket of steam and gas without the direct involvement of molten magma. Eruptive activity at ‘La Fossa’ Volcano, Island of Vulcano (Italy), typically starts with a phreatic explosion, continues as phreatomagmatic and turns into a late magmatic stage, depending on the reduction in the efficiency of magma-water interaction. The present risk is mainly related to a village located at the very foot of the active volcanic cone, which in summer seasons is inhabited by more than 10,000 people. Because the last eruptive episode occurred in 1888–1890, when no local instrumental control was performed, the scientific community does not have any information about the seismic phenomena which could precede the initial phreatic blast. Inferences from similar monitored volcanoes, which awakened in the last few years after more or less long quiescence, are therefore made to tentatively depict possible pre-eruptive seismic scenarios and also to evaluate the most appropriate surveillance and alert criteria to adopt. Appreciable signs of volcanic unrest have been detected in recent years, mainly related to modifications in the physical and chemical features of fumarolic fluids discharged at the active crater. Following the classification of local seismic shocks, the recording oflong-period events (peak frequency ≤2 Hz) should be taken into account as a realistic seismic warning of volcanic hazard enhancement. A likely short-term seismic precursor may be finally given by the appearance of the so-calledbanded tremor, a seismic signal likely produced by intermittent hydrothermal boiling accompanying the hydraulic fracturing of rocks at the top of a pressurized aquifer. Real-time recognition of tremor can be therefore very useful to avoid, at least, injuries to volcanologists and visitors working or staying on the most dangerous sectors of the volcano.

Earthquake source nucleation: a physical model for short-term precursors : Ohnaka, M TectonophysicsV211, N1/4, Sept 1992, P149–178

Earthquake source nucleation: a physical model for short-term precursors : Ohnaka, M TectonophysicsV211, N1/4, Sept 1992, P149–178

A review on phreatic eruptions and their precursors

Abstract An analysis of the reported information on 132 historical phreatic events indicates that most of these (115) were not followed by a magmatic or phreatomagmatic eruption. Only in 18 cases precursory phenomena are reportedly lacking, whereas they are recognized for the majority (72) of the considered cases. These precursors have been analyzed as a function of the kind of phreatic event and of its possible triggering mechanism. Unfortunately, the quality of the available information is poor. However, data suggest that anomalous seismicity, ground deformation, changes in the output, chemistry and temperature of fumaroles and thermal springs are potential mid-term precursors, whereas seismic tremor is a common short-term precursor.

Earthquake source nucleation: A physical model for short-term precursors

Ohnaka, M., 1992. Earthquake source nucleation: a physical model for short-term precursors. In: T. Mikumo, K. Aki, M. Ohnaka, L.J. Ruff and P.K.P. Spudich (Editors), Earthquake Source Physics and Earthquake Precursors. Tectonophysics, 211: 149–178. This paper deals with a quasistatic, leading to a quasidynamic at a later time, nucleation process that precedes the earthquake dynamic rupture, and models of the earthquake source nucleation are put forward based on physical principles. A quasistatic to quasidynamic rupture nucleation process is an intrinsic part of the ensuing earthquake dynamic rupture; in other words, the nucleation process itself is an short-term (or immediate) precursor that occurs in a localized zone. During the earthquake nucleation, premonitory slip proceeds in the localized nucleation zone, and shear stress also decreases gradually in the zone, since slip-weakening occurs during the nucleation. Immediate foreshock activity is a part of the nucleation process leading to the mainshock dynamic rupture; therefore, hypocentral locations of foreshocks are necessarily restricted to lie near the mainshock hypocentre (onset of the mainshock rupture). Whether or not foreshocks occur during the mainshock nucleation depends on how the rupture growth resistance varies on a local to small scale. Since patches of greater rupture growth resistance are considered to prevail on a local to small scale in the fault zone, carrying immediate foreshocks would be one of the major characteristics of earthquakes that nucleate within the brittle seismogenic layer. When a mainshock earthquake nucleates within the brittle seismogenic layer and its hypocentre is located near the base of the seismogenic layer, immediate foreshocks for this mainshock are necessarily restricted to lie within a localized region shallower than hypocentral depth of the mainshock. By contrast, the nucleation process below the base of the seismogenic layer is aseismic in nature, so that carrying no conspicuous foreshocks would be a common characteristic of interplate earthquakes that nucleate below the base of the brittle seismogenic layer. The breakdown strength τ p , the breakdown stress drop Δτ b and the critical slip displacement D c are indicative of the rupture growth resistance. To estimate depth variations of these parameters, the effects of the normal stress σ n and temperature T on those parameters are examined using available data so far published. The combined effects of σ n and T on τ p in the brittle to semibrittle regime are found to be represented empirically by: τ p(σ n, T) = τ pO(σ n)[1−(cosh 50 T ) + 40 sinh( 50 T ) exp(− 2000 T ] where τ po ( σ n ) = 135.7 + 0.750 σ n , and T is measured in °K and σ n in MPa. It is found that D c increases sharply with T, but is insensitive to σ n above 300°C, while D c depends on σ n but is insensitive to T below 300°C. On the basis of these results, variations in τ p, D c and Δτ b at mid-crustal depths are estimated for quartzo-feldspathic rocks for a given geothermal gradient.

地震の前兆現象発生のメカニズム

The process of the occurrence of an earthquake is discussed from the mechanical point of view, and it is emphasized that the structural heterogeneity in and around the earthquake source region is one of the most important factors which cause the occurrence of precursory phenomena. Earthquake precursors are classified into the following two types. The one is the precursors which are caused by the increase in stress. In general, long-term precursors are those of this type. The gradual increase of earthquake swarm activity before the 1983 Japan Sea earthquake, the gradual increase in seismic activity in the surrounding region of the 1989 Loma Prieta earthquake before the main shock and the appearence of the seismic gaps of the second kind are discussed as examples of this type. The other is the precursors which are caused by a slowly progressive rupture process just before the sudden main fracture. Short-term precursors are mainly those of tis type. Foreshocks prior to the 1934 and 1966 Parkfield earthquakes are discussed as the typical examples of this type.

Constraints on the usefulness of gravimetry for detecting precursory crustal deformations

The detectability of gravity changes arising from preseismic processes in the source region of an earthquake depends on the nature of the process, the magnitude of the impending event, the distance from the hypocentre and the background noise level. Using typical background spectra from recording spring-type gravimeters, superconducting gravimeters and long-term gravity network surveys, we have calculated the feasibility of detecting gravity precursors to thrust-type earthquakes. As a result of the 1/ f 2 nature of the gravity noise power spectral density the detectability of precursors by recording gravimeters depends on the rate of build-up (amplitude over rise time) as well as on the ultimate amplitude of the preseismic anomaly. Ruling out site-specific fluid effects, the maximum possible amplitude of the precursory gravity signal can be estimated for both preseismic dilatant volume expansion and preseismic dip-slip as a function of earthquake magnitude and depth. Combining these results shows that detection of gravity precursors over a wide range of possible rise times (minutes to years) would require a network of ten to fifteen recording superconducting gravimeters tied by regular bi-weekly high-precision gravity measurements distributed over a 30 × 30 km area where there was a reasonable expectation of seismic events in the range M = 6 to 7 at depths of no more than 10–20 km. If monitoring were restricted to a search for short-term precursors (minutes to hours) over a subduction zone, an unconnected network of superconducting gravimeters could be expected to detect gravity effects resulting from precursory aseismic slip prior to an M = 6 event under certain conditions.

Volcanomagnetic effect observed during the 1986 eruption of Izu-Oshima Volcano.

Remarkable changes in the total geomagnetic intensity were observed associated with the 1986 eruption of the Izu-Oshima Volcano. They are summarized as follows: (1) Long-term precursor: decrease in the total intensity at one station on the southern slope of the central cone, Miharayama, continued since 1981, with a constant rate of -5nT/yr. (2) Middle-term precursor: the decrease there accelerated beginning in April, 1986. (3) Short-term precursor: in October, 1986, an increase in the total intensity was observed at two stations on the north side of Miharayama, while readings at two southern stations decreased. (4) At the first stage of the Phase I eruption, step-like changes were observed at the two southern stations. (5) A decrease in the total intensity was observed at two other stations outside the caldera at the time of the fissure eruption on November 21, and a few survey points and one station showed significant changes. (6) For a few months after the eruption, no remarkable magnetic variations were found outside the caldera.(1), (2) and (3) are interpreted as thermal demagnetization of vent materials due to high-temperature volatiles dispatched from ascending magma. (4) is most likely due to rotation of vent materials. (5) is attributed to the piezomagnetic effect, together with the thermal demagnetization, due to intrusive dykes. In the 1950 eruption a demagnetized area with a 2km radius was formed at a depth of 5km (RIKITAKE, 1951a). In contrast, during the Phase II activity on November 21 and 22, 1986, an intrusive event is suggested to have occurred beneath the southeastern region of the volcano, as inferred from the observed total field changes.

Theory of electrokinetic effects occurring at the final stage in the preparation of a tectonic earthquake

Crustal deformation processes occur with relative rapidity when short-term precursors appear at the final preparatory stage of a tectonic earthquake. This paper contains calculations of crustal bulk strain before an earthquake, based on the model of a rigid inclusion. The data give initial conditions for the problem of fluid percolation in a two-phase medium accompanied by electrokinetic effects. The solution provides a description of systems of currents arising in the vicinity of the source region. An analysis of this theoretical evidence yields information on the behaviour of short-term precursors in telluric currents and the geomagnetic field.

On intermediate-term prediction of strong earthquakes in the Himalayan arc region using pattern recognition algorithm M8

Seismicity of the Himalayan arc lying within the limits shown in figure 1 and covering the period 1964 to 1987 was scanned using M8 algorithm with a view to identifying the times of increased probabilities (TIPs) of the occurrence of earthquakes of magnitude greater than or equal to 7·0, during the period 1970 to 1987. In this period, TIPs occupy 18% of the space time considered. One of these precedes the only earthquake in this magnitude range which occurred during the period. Two numerical parameters used in the algorithm, namely the magnitude thresholds, had to be altered for the present study owing to incomplete data. Further monitoring of TIPs is however warranted, both for testing the predictive capability of this algorithm in the Himalayan region and for creating a base for the search of short-term precursors.

Earthquake swarms as short-term precursors in the Dalton-Gunning region, 34.70–34.86°S, 149.11–149.26°E, New South Wales, Australia

Abstract From January 1, 1960 to June 30, 1987, 29 swarms and swarm groups have been identified in the Dalton-Gunning region, Australia. Sixteen of these were followed by larger events related to them. If M p is the mean Richter magnitude of the three largest events of a swarm and Mm is the magnitude of the subsequent main shock, then the 16 cases fit the regression M m = (0.93 ± 0.18) M p + (0.92 ± 0.36) Fourteen of the 16 swarms were followed by a main shock within 60 days, so there is a probability of ∼ 48% that any swarm will be followed by a related main shock within this time period. This is more useful than earthquake risk statistics for forecasting events with 2.6 ⩽ Mm ⩽ 3.6, as the largest event related to a precursory swarm had magnitude ML 3.6. However, many events, including the only two potentially damaging earthquakes in the region since the commencement of detailed seismological recording, would not have been forecast by swarms.

Variation of dispersion of radon content in the groundwater and short-term and imminent precursors of earthquakes

A lot of observational data both at home and abroad suggested that before some strong earthquakes anomalous variations of radon concentration appear in the chemical composition of groundwater. In order to further study these anomalies and get reliable precursory anomalies, a special packet of precursory data processing has been developed recently. By using a computer program of first-order difference method, it is discovered that the scatter of radon content increased systematically before earthquakes at some observation posts where observational conditions are fairly good. This change may be a new criterion for evaluating short-term and imminent earthquake precursors.

Two categories of earthquake precursors, physical and tectonic, and their roles in intermediate-term earthquake prediction

I suggest that earthquake precursors can be divided into two major categories, physical and tectonic. I define physical precursor to be a direct or indirect indication of initiation or progression of an irreversible rupture-generating physical process within the preparation zone of a forthcoming earthquake. Tectonic precursor is defined as a manifestation of tectonic movement which takes place outside the preparation zone of an impending earthquake as a link in a chain of particular local tectonism in each individual area preceding the earthquake. Most intermediate-term, short-term and immediate precursors of various disciplines within the source regions of main shocks are considered physical ones. Some precursory crustal deformations around the source regions are, however, possibly tectonic precursors, because they may be caused by episodic plate motions or resultant block movements in the neighboring regions of the fault segments that will break. A possible example of this phenomena is the anomalous crustal uplift in the Izu Peninsula, Japan, before the 1978 Izu-Oshima earthquake ofM s 6.8. Some precursory changes in seismicity patterns in wide areas surrounding source regions also seem to be tectonic precursors, because they were probably caused by the particular tectonic setting of each region. A typical example is a so-called doughnut pattern before the 1923 Kanto, Japan, earthquake ofM s 8.2. Although most studies on earthquake precursors so far seem to regard implicitly all precursory phenomena observed as physical ones, the two categories should be distinguished carefully when statistical analysis or physical modeling is carried out based on reported precursory phenomena. In active plate boundary zones, where a practical strategy for earthquake prediction may well be different from that in intraplate regions, tectonic precursors can be powerful additional tools for intermediate-term earthquake prediction.