Impending Earthquake Research Articles

On the recent advances in the study of seismic electric signals (VAN method)

Seismic electric signals (SES) are low frequency (⩽1 Hz) changes of the electric field of the earth that have been first observed in Greece [Varotsos, P., Alexopoulos, K., Nomicos, K., 1981a. Seismic electric currents. Pract. Athens Acad. 56, 277–286; Varotsos, P., Alexopoulos, K., Nomicos, K., 1981b. Seven-hour precursors to earthquakes determined from telluric currents. Pract. Athens Acad. 56, 417–433; Varotsos, P., Alexopoulos, K., 1984a. Physical properties of the variations of the electric field of the earth preceding earthquakes, I. Tectonophysics 110, 73–98; Varotsos, P., Alexopoulos, K., 1984b. Physical properties of the variations of the electric field of the earth preceding earthquakes, II. Tectonophysics 110, 99–125] to precede earthquakes, with a lead time from several hours to a couple of months. Here, we review the recent advances on the SES observation and analysis, main points of which are the following: First, at epicentral distances of the order of 100 km, the SES electric field precedes markedly the time-derivative of the magnetic field; this finds applications in the determination of the epicenter of the impending earthquake and in the distinction between true SES and noise emitted from artificial sources. Second, a detectable difference in the time evolutions of the electric field components of SES exists, which can also be used for the determination of the epicenter of the impending earthquake. Third, the analysis of SES is significantly advanced in a recently introduced [Varotsos, P., Sarlis, N., Skordas, E., 2001. Spatio-temporal complexity aspects on the interrelation between seismic electric signals and seismicity. Pract. Athens Acad. 76, 294–321; Varotsos, P., Sarlis, N., Skordas, E., 2002a. Long-range correlations in the electric signals that precede rupture. Phys. Rev. E 66, 011902] new time-domain, termed as natural time domain. This has been inspired from the theory of critical phenomena, which has been suggested long ago by our group. The natural time-domain, beyond other applications in diverse fields, enables the distinction of similar looking electric signals that are emitted from systems of different dynamics as well as provides a better estimation for the time window of an impending mainshock. The spectral content of the seismic activity in natural time, evolves consecutively in time upon the occurrence of every new event, and finally coincides to that of the SES a few hours to a few days before the mainshock, thus allowing the estimation of the occurrence time of the impending mainshock with an accuracy that was not hitherto available.

Diagnosis of Time of Increased Probability (TIP) for Volcanic Earthquakes at Mt. Vesuvius

The possibility of intermediate-term earthquake prediction at Mt. Vesuvius by means of the CN algorithm is explored. CN was originally designed to identify the Times of Increased Probability (TIPs) for the occurrence of strong tectonic earthquakes, with magnitude M ≥ M0, within a region a priori delimited. Here the CN algorithm is applied, for the first time, to the analysis of volcanic seismicity. The earthquakes recorded at Mt. Vesuvius during the period from February 1972 to June 2004 are considered, and the magnitude threshold M0 selecting the events to be predicted is varied within the range: 3.0–3.3. Satisfactory prediction results are obtained, by retrospective analysis, when a time scaling is introduced. In particular, when the length of the time windows is reduced by a factor 2.5–3, with respect to the standard version of CN algorithm, more than 90% of the events with M ≥ M0 occur within the TIP intervals, with TIPs occupying about 30% of the total time considered. The control experiment ``Seismic History'' demonstrates the stability of the obtained results and indicates that the CN algorithm can be applied to monitor the preparation of impending earthquakes with M ≥ 3.0 at Mt. Vesuvius.

PS-100 anti-interference electrical observation system and its application to earthquake prediction study

A chief problem encountered in georesistivity observation, namely interference from electromagnetic noise in measuring process, is discussed in this paper. The application of a new set of electric observation system PS-100, in Sichuan and Yunnan provinces, southwest China, is reported. The observation data from the four newly established stations indicates that the precision of the hourly georesistivity value reached 0.2% for the first time, and also that the CDMA-based PS-100 system has the high power of anti-interference ability, i.e. the capability to eliminate the influence of EM noise in georesistivity observations. Prior to the Ms5.6 Ludian earthquake on August 10, 2004, Yunnan province, co-seismic effect was recorded for the first time at Mianning station, which is 200 km far from the epicenter. The focal mechanism of the Ms5.6 event shows that Mianning station is situated at the compressive part of the primary wave Pn, which is consistent with the co-seismic georesistivity change. A change in georesistivity similar to that of gravity tide of M2 was observed at Mianning station, which can be interpreted as the of the stiffness tending to zero for the media at its surrounding area, and this may provide an example for the ‘model of impending earthquake precursor of geoelectricity triggered by tidal forces’.

The central Philippine Fault Zone: Location of great earthquakes, slow events and creep activity

AbstractThe central Philippine Fault Zone is found to be the locus of great earthquakes, a transition zone with slow slip and creep activity. This is based on the analysis and correlation of seismic historic data and detailed documentation of recent seismic events in the region. Based on this study the Guinyangan fault is defined to be the northern locked portion with recurrence interval of as short as 65 years. The Masbate fault is the central part with large and medium earthquakes accompanied by unusually large ground rupture. The north Central Leyte fault and the south Central Leyte fault, on the other hand, are characterized by aseismic creep and medium-sized events, usually with clusters of foreshocks, respectively. Unusual seismic activity both on the Masbate fault and Central Leyte fault somehow correlates well with the behavior of known slow events and creep activity. Further investigation of this region could lead to deeper understanding of impending major earthquakes, especially along the Guinyangan fault, which usually produces larger damaging events, and for further understanding of the impact of slow events and creep on the adjoining active structures.

Extracting preseismic electromagnetic signatures in terms of symbolic dynamics

Abstract. When a heterogeneous material is strained, its evolution toward breaking is characterized by the nucleation and the coalescence of micro-cracks before the final break-up. Electromagnetic (EM) emission in a wide frequency spectrum ranging from very low frequencies (VLF) to very high frequencies (VHF) is produced by micro-cracks, which can be considered as the so-called precursors of general fracture. Herein we consider earthquakes (EQs) as large-scale fracture phenomena. We study the capability of nonlinear time series analysis to extract features from pre-seismic electromagnetic (EM) activity possibly indicating the nucleation of the impending EQ. In particular, we want to quantify and to visualize temporal changes of the complexity into consecutive time-windows of the time series. In this direction the original continuous time EM data is projected to a linguistic symbolic sequence and then we calculate the block entropies of the optimal partition. This analysis reveals a significant reduction of complexity of the underlying fracto-electromagnetic mechanism as the catastrophic events is approaching. We verify this result in terms of correlation dimension analysis. We point out that these findings are compatible with results from an independent linear method which uses a wavelet based approach for the estimation of fractal spectral characteristics. Field and laboratory experiments associate the epoch of low complexity in the tail of the precursory emission with the nucleation phase of the impending earthquake.

Time-difference between the electric field components of signals prior to major earthquakes

We present data demonstrating that the electric field components of low-frequency (⩽1Hz) precursory electric signals exhibit markedly different time evolutions. This difference, if properly measured, upon considering that the electromagnetic fields obey diffusion-type equations, is of profound importance since it can reveal the distance of the measuring site from the epicenter of the impending earthquake.

Reply to "Comment on 'Systematic Analysis of Shear-Wave Splitting in the Aftershock Zone of the 1999 Chi-Chi, Taiwan, Earthquake: Shallow Crustal Anisotropy and Lack of Precursory Changes,' by Yunfeng Liu, Ta-Liang Teng, and Yehuda Ben-Zion," by Stuart Crampin and Yuan Gao

We thank Crampin and Gao (2005, hereinafter referred to as cg) for their interest in the analysis and results of Liu et al. (2004, hereinafter referred to as ltbz). We disagree that the lines they draw through some of the data points of figure 14a of ltbz (reproduced here as Fig. 1) carry quantitative scientific information, and we maintain our assessment that the results of ltbz do not show systematic temporal evolution of anisotropy parameters that could be used to forecast impending large earthquakes in our study area. Our response to cg focuses on features involving directly the results of ltbz. We do not discuss the broader claims of cg on general scaling relations, associated with their figures 2 and 3, other than to note that they have been controversial (e.g., Aster et al. , 1990, 1991; Seher and Main, 2004). Prompted by the comment of cg, we perform a more detailed analysis of spatio-temporal variations of the time delays between fast and slow shear waves in our data. The detailed examination indicates clearly that the apparent precursory pattern identified by cg is dominated by spatial rather than temporal variations of properties. Figure 1. Observed time-delay values for the section deeper than 0.2 km versus time. Each data point is a time-delay measurement with an error given by the vertical line. The mean values and standard deviations of the measurements before and after the Chi-Chi mainshock are indicated by solid and dashed lines, respectively. The numbers near the points mark the sequential ordering of the measurements. Figure 1 is an enlarged version of figure 14a of ltbz, with sequential numbering of the data points before the 1999 Chi-Chi mainshock and several later points. The “subtle temporal changes” referred to by cg are associated with a …

Comment on "Systematic Analysis of Shear-Wave Splitting in the Aftershock Zone of the 1999 Chi-Chi, Taiwan, Earthquake: Shallow Crustal Anisotropy and Lack of Precursory Changes, by Yungfeng Liu, Ta-Liang Teng, and Yehuda Ben-Zion"

Liu et al. (2004) systematically analyze the parameters of shear-wave splitting before and after the 1999 Chi-Chi earthquake in Taiwan. They claim that they see no evidence for the temporal changes in shear-wave time delays, which some of us use to monitor the buildup of stress before earthquakes. In fact, the only diagram where one would expect to see the type of temporal changes observed elsewhere, figure 14a in Liu et al. (2004), does show two types of temporal variations of time delays. Here, we fit least-squares lines to these temporal changes and show that the duration/earthquake-magnitude relationships of these various changes agree very well with those seen elsewhere. Thus, the behavior before the Chi-Chi earthquake lends further support to the use of shear-wave splitting to stress-forecast the times and magnitudes of impending earthquakes.

宮城県の津波対策について

With an impending earthquake off the coast of Miyagi Prefecture together with the occurrence of an endangering tsunami, Miyagi Prefecture's important role in control and a model project that is to be considered by a collaboration of residents and government organizations will be presented.

Spatio temporal seismicity variation in earthquakes of Uttaranchal region

The spatio temporal variations of seismicity preceding Uttarkashi, 1991 and Chamoli, 1999 earthquakes were studied based on the data during the period 1981 to 2000 using the catalogues of earthquakes prepared by the India Meteorological Department. Two scenarios were examined. In one case the epicentral distance from the respective impending earthquakes were worked out for all the earthquakes recorded during a ten years period prior to the earthquake of Uttarkashi and Chamoli respectively. In the other case, the epicenter near latitude 30.2° N and longitude 80.2° E near India Nepal border (where earthquakes of 1966 and 1980 occurred) were considered to compute the epicentral distance. The second case was included because it is a seismically active region where Dharachulla earthquake of 1916 (magnitude 7.5) occurred. The earthquakes of 1999, 1991 and 1980 in Uttaranchal were characterised by six phases of seismic activity namely (i) first quiescence or gap, (ii) swarm, (iii) second quiescence or gap, (iv) foreshocks, (v) main shock and (vi) aftershocks. Some differences among these phases could however, be noticed which were explained through source mechanism, isoseismals, ‘b’ (Gutenberg Richter’s relationship), ‘h’ values (Omori’s law ) and fractal dimension. It is interesting to point out that prior to the occurrence of earthquake swarms (second phase) the seismic pattern exhibits the development of a seismic gap (first phase) after the decay of the aftershock activity associated with a previous large earthquake of magnitude greater than or equal to M: 6.0 in this region. We infer that this second ‘gap’ (third phase) is a characteristic of the complexity of the tectonics in the Uttaranchal. Thus, the simple Kanamori’s asperity model could be modified to consist of six phases of seismic activity in the complex tectonic zone of Garhwal Himalaya. Detailed difference in the seismicity patterns prior to the earthquake were explained by the fractal dimensions estimated from the ‘b’values.

Observations of stress relaxation before earthquakes

SUMMARY Theory and observations suggest that seismic shear wave splitting, caused by fluid-saturated stress-aligned microcracks, directly monitors low-level deformation before fracturing, faulting and earthquakes occur. In the past, it had been assumed that the accumulation of stress before earthquakes continued until stress was released by faulting at the time of the earthquake. However, new data and reappraisal of existing data sets now suggests that the stress begins to relax and cracks close from tens of minutes to months before the earthquake actually occurs, with the logarithm of the duration of the relaxation proportional to the magnitude of the impending earthquake. The duration of the relaxation appears to be directly correlated with earthquake magnitude, and may have implications for the earthquake source process and the ability to predict earthquakes.

Experience of short term earthquake precursors with VLF–VHF electromagnetic emissions

Abstract. Electromagnetic anomalies (EMA) covering a wide range of frequencies from ULF, VLF up to VHF have been observed before recent destructive earthquakes in continental Greece. We show that the features of these signals are possibly correlated with the fault model characteristics of the associated earthquake and with the degree of geotectonic heterogeneity within the focal zone. The time evolution of these electromagnetic sequences reveals striking similarities to that observed in laboratory acoustic and electromagnetic emissions during different stages of failure preparation process in rocks. If we consider that the same dynamics governs the large-scale earthquakes and the microscopic scale sample rheological structure, the results of this analysis suggest that the recorded EMA might reflect the nucleation phase of the associated impending earthquake. We focus on the rise of the statistical view of earthquakes. We find electro-magnetic fingerprints of an underlying critical mechanism. Finally, we conclude that it is useful to combine ULF and VLF-VHF field measurements in an attempt to enhance the understanding of the physics behind these observations and thus to improve the quality of earthquake prediction. Further, the identification of an EMA as a seismogenic one supports the characterization of a sequence of shocks as foreshocks at the time they occur, further helping the earthquake prediction effort.

Search for earthquake precursors in multidisciplinary data monitoring of geophysical and biological parameters

Abstract. Short-term variations in sets of geophysical and biological parameters that were monitored at the Garm research site for a long time are considered in relation to an earthquake of magnitude M = 5.3. Daily average data of electrical resistivity, electrototelluric field, electrochemical potential, water conductivity and hourly average data of electrical activity of weakly electric fishes were used. All the data, including bioindicators activity, were obtained by high precision instrumental methods. Contemporary disturbances of all the geoelectrical parameters were discovered when observations were carried out directly in the epicentral zone of the impending earthquake. At the distance of about 20–30 km from the epicenter short-term precursors were not found.

Earthquake epicentroids in the Beijing-Tianjin-Tangshan-Zhangjiakou region inversed by gravity variation data

Gravity variation data observed in the process of seismogenesis and occurrences of earthquakes show that the location with the greatest gravity changes does not necessarily coincide with the epicenter. To explain this we defined the center of effective mass of stress volume as "hypocentroid", and the vertical projection of which on the earth’s surface as "epicentroid". Here we adopt three rotating models, including spheroid, ellipsoid and cylinder, to represent the region of an impending earthquake. Based on the models of gravity variations induced by uniform dilatancy, epicentroids associated with sixteen earthquakes with M>4.0 occurred in 1981–2000 in the Beijing-Tianjin-Tangshan-Zhangjiakou region are determined by means of a proposed least squares iterative inversion method. The results indicate that cylinder model is preferable to the other two, and epicentroids obtained by the cylinder model separate from the epicenters by a range of 0–40 km. Epicentroids are inevitably located within intact tectonic blocks, and usually cluster in groups; while the epicenters are generally located at the terminations of faults or at the intersections of faults. It seems that there exist earthquake-hatching areas in the block among faults. Earthquakes hatch in these areas, but occur around these areas, meanwhile the existence of faults may play an important role in controlling the processes.

Speculations on Earthquake Forecasting

A new understanding of the way fluid-saturated microcracked rocks deform suggests that networks of stress-monitoring sites could lead to earthquake forecasting analogous to the way networks of meteorological stations allow weather forecasting and prediction of storms. This new understanding is believed to be a major advance that otters more hope for forecasting earthquakes than was envisioned in the survey Living on an Active Earth: Perspectives on Earthquake Science of the National Research Council's Committee on the Science of Earthquakes, summarized by Tom Jordan in the Opinion for August 2002. This Opinion may also be considered as a response to the plea by John E. Ebel in the Opinion for January 2003, for seismologists to begin forecasting earthquakes. This note was stimulated by confirmation of the complex critical nature of deformation at a stress-monitoring site in Iceland and its implications for the NRC report on earthquake science. The linearity and self-similarity of the well known Gutenberg-Richter relationship demonstrate that the Earth behaves as a complex critical system with self-organized criticality, where minor disturbances (small earthquakes or fractures) may cascade into major fractures and large earthquakes. Such criticality is claimed to specifically exclude the possibility of the deterministic prediction of the time, magnitude, and location of impending large earthquakes. Resolving this fundamental difficulty is one of the four complementary perspectives of earthquake research recognized by the NRC report, and as Jordan suggests provides “the opportunity for exciting basic science.” We here speculate on some of this new exciting science. Although as suggested criticality makes the deterministic prediction of the time, magnitude, and location of impending large earthquakes rather unlikely, large earthquakes cannot take place without the accumulation of sufficient stress for the appropriate magnitude energy release. Both observations and the theory of the evolution of fluid-saturated microcracked rock under stress ( anisotropic poro-elasticity …

Mechanical coupling between the Landers and Hector Mine (California) fault systems

A 2D finite element approach is used to model the mechanical coupling between faults and the interaction between large earthquakes. The regional tectonic stress, the fault geometry and the Coulomb friction law control the resulting slip patterns. To test the potential of this approach we investigate the Landers and Hector Mine earthquakes which occurred in southern California. The resulting coseismic displacement satisfactorily fits the available GPS data. We show that the stress changes induced by the 1992 MW = 7.3 Landers earthquake modulate the applied regional tectonic stress reducing the slip on the faults of the subsequent 1999 MW = 7.1 Hector Mine rupture. We emphasize that fault interaction due to stress transfer can alter the slip distribution of impending earthquakes.

Advance earthquake warnings

Urban centers can receive a 15‐to‐30‐second advance warning about impending earthquakes if several technical criteria are met, according to a study by Ta‐liang (Leon) Teng of the Southern California Earthquake Center and Yih‐Min Wu of the Taiwan Central Weather Bureau. The study is published in the Bulletin of the Seismological Society of America, vol. 92, no. 5, June 2002).Teng and Wu's system for developing early warnings for earthquakes relies on data from a “virtual sub‐network” automatically established when an earthquake triggers a group of nearby seismic stations. That information can then be immediately distributed as an early warning.

Precursory accelerating seismic crustal deformation in the Northwestern Anatolia Fault Zone

We present the results of a systematic search for the identification of accelerating seismic crustal deformation in the broader northern Aegean area and in northwestern Turkey. We found that accelerating seismic deformation release, expressed by the generation of intermediate magnitude earthquakes, is currently observed in NW Turkey. On the basis of the critical earthquake model and by applying certain constraints which hold between the basic quantities involved in this phenomenon, it can be expected that this accelerating seismic activity may culminate in the generation of two strong earthquakes in this area during the next few years. The estimated epicenter coordinates of the larger of these probably impending earthquakes are 39.7°N–28.8°E, its magnitude is 7.0 and its occurrence time t c=2003.5. The second strong event is expected to occur at t c=2002.5 with a magnitude equal to 6.4 and epicenter coordinates 40.0°N–27.4°E. The uncertainties in the calculated focal parameters for these expected events are of the order of 100 km for the epicenter, ±0.5 for their magnitude and ±1.5 years for their occurrence time.

The use of an outlier detecting method in time series of continuous daily measurements of underground water level and temperature in earthquake prediction investigation

Continuous daily measurements of underground water level and temperature have been monitored in four selected shallow wells in a seismically active area close to Thessaloniki, Greece. The aim was to study the changes in the underground water level and temperature with respect to earthquakes occurring in the same area during 1 January 1988 to 31 December 1989. A graphical method has been applied to analyze the time series in order to detect outliers. Our results reveal that a strong correlation exists the earthquakes occurred in the area, and the water level time series. The correlation was found to be weak in the case of the water temperature time series. Most of the outliers found correspond to a time interval varying between 1 and 7 days before or after the earthquakes. The magnitude of the underground water level change varies from 3 to 10 cm, and that of temperature from 0.3 to 0.8°C. The strongest outliers correlate to earthquakes of magnitude greater than 3.0. The software developed to detect outliers, use immediate preceding observations in the time series of continuous daily measurements, at the time of their occurrence. This is very important in studying precursory phenomena of impending earthquakes.

Relaxation creep model of impending earthquake

The alternative view of the current status and perspective of seismic prediction studies is discussed. In the problem of ascertainment of the uncertainty relation Cognoscibility-Unpredictability of Earthquakes, priorities of works on short-term earthquake prediction are defined due to the advantage that the final stage of nucleation of earthquake is characterized by a substantial activation of the process while its strain rate increases by the orders of magnitude and considerably increased signal-to-noise ratio. Based on the creep phenomenon under stress relaxation conditions, a model is proposed to explain different images of precursors of impending tectonic earthquakes. The onset of tertiary creep appears to correspond to the onset of instability and inevitably fails unless it is unloaded. At this stage, the process acquires the self-regulating character and to the greatest extent the property of irreversibility, one of the important components of prediction reliability. Data in situ suggest a principal possibility to diagnose the process of preparation by ground measurements of strain-rate-dependent parameters, like electromagnetic emission, etc. Laboratory tests of the measurements of acoustic and electromagnetic emission in the rocks under constant strain in the condition of self-relaxed stress until the moment of fracture are discussed in context. It was obtained that electromagnetic emission precedes but does not accompany the phase of macrocrack development.