Impending Earthquake Research Articles

Impending HRT wave precursors to the Wenchuan M s8.0 earthquake and methods of earthquake impending prediction by using HRT wave

We deployed four geo-electric monitoring stations in Sichuan and Yunnan provinces from 2004, using the new generation of equipment (PS-100) and technologies to capture the HRT wave earthquake precursor. Before the Wenchuan Ms8.0 earthquake, we recorded the HRT wave precursor at the only operating station in Hongge (HG, Δ=465 km) and found that significant impending signal had been recorded at the station in the early morning (0–5 am) of 12th of May, 2008. The precursor for this earthquake is consistent with precursors recorded for other strong earthquakes. The measured physical properties (geo-resistivity and telluric-current) show tidal wave period oscillations from several days to several months before the earthquakes and the amplitude of such HT oscillation increases significantly towards the occurrence of an earthquake. These HT and RT waves from the epicenter have a causal relationship with the earthquakes that happened several days later. The arrival time of two RT waves is proportional to the distance from the station to the epicenter. The estimated natural decay of the amplitude is correlated with the natural period (T0) of the earthquake fault, which is proportional to the fault length. From this relationship, we can predict the earthquake magnitude. For magnitude 6–9 earthquakes, the natural period is about 1–6 hours. Such oscillation comes from the epicenter area and they can propagate several thousand kilometers in the Earth’s crust. Before a strong earthquake in the shallow crust, the conductive pore fluid will experience major changes before the fault rapture. Such fluid change will emit an oscillation in the pore fluid pressure. This is the mechanism for the HRT wave generation. Since the China Earthquake Administration funded the HRT wave short-term earthquake prediction project in 2003, the first record of HRT precursor wave has been recorded from the 2004-12-26 Sumatra Mw9.0 earthquake with the largest epicentre distance Δ=2900 km. Thereafter, we have captured HRT waves from more than twenty strong earthquakes, which are well-matched and show repeatability, consistency and regularity. All our observation with the HRT waves demonstrate that HRT wave precursors to earthquakes indeed exist. Strong earthquakes can be predicted and short-term and impending earthquake prediction is achievable in the very near future. From all the observations, including the ones at HG station from Wenchuan Ms8.0 earthquake, we conclude that using HRT wave to predict earthquakes is feasible.

Parkfield revisited: I. Data retrieval

The Parkfield earthquake prediction experiment (1985–2004) was designed to monitor stress accumulation in the lithosphere related to an impending earthquake on the San Andreas fault. However, no precursory signals were detected prior to the 2004 Parkfield earthquake (M6.0). In this paper we re-examine the long-term borehole strain records at Parkfield (Langbein et al., 2006). We find that they are consistent with a stationary tectonic stress field on the order of 55 MPa in the direction of the fault. This is the first measurement of far-field tectonic stresses from borehole strainmeter records. It suggests that logarithmic creep strains from boreholes can be used to interpret the state of stress in the lithosphere surrounding the San Andreas fault.

Discrimination between pre-seismic electromagnetic anomalies and solar activity effects

Laboratory studies suggest that electromagnetic emissions in a wide frequency spectrum ranging from kilohertz (kHz) to very high megahertz (MHz) frequencies are produced by the opening of microcracks, with the MHz radiation appearing earlier than the kHz radiation. Earthquakes are large-scale fracture phenomena in the Earth's heterogeneous crust. Thus, the radiated kHz–MHz electromagnetic emissions are detectable not only in the laboratory but also at a geological scale. Clear MHz-to-kHz electromagnetic anomalies have been systematically detected over periods ranging from a few days to a few hours prior to recent destructive earthquakes in Greece. We should bear in mind that whether electromagnetic precursors to earthquakes exist is an important question not only for earthquake prediction but mainly for understanding the physical processes of earthquake generation. An open question in this field of research is the classification of a detected electromagnetic anomaly as a pre-seismic signal associated with earthquake occurrence. Indeed, electromagnetic fluctuations in the frequency range of MHz are known to be related to a few sources, including atmospheric noise (due to lightning), man-made composite noise, solar–terrestrial noise (resulting from the Sun–solar wind–magnetosphere–ionosphere–Earth's surface chain) or cosmic noise, and finally, the lithospheric effect, namely pre-seismic activity. We focus on this point in this paper. We suggest that if a combination of detected kHz and MHz electromagnetic anomalies satisfies the set of criteria presented herein, these anomalies could be considered as candidate precursory phenomena of an impending earthquake.

Source Ruptures and Deep Processes of Great Earthquakes and Short‐Term and Impending Earthquake Prediction

AbstractResponse to tectonic stress, micro ruptures will be produced in media within and surrounding a seismic source. With steady building up of stress, these ruptures will grow to become a rupture chain of some scale, indicative of a critical state of stress concentration. At this moment, the accumulated giant energy in the source is released suddenly in seismic waves propagating outward, producing a series of destructions and large faults on the surface. After a major shock occurs, using a proper model, seismic records at near and far stations as well as calculation of focal mechanisms, we can determine the rupture length and rupture processes of the seismic source. Observations show that during the generation and occurrence of a major or large earthquake, ruptures occur in the source as well as on the surface, which are of lengths several, tens or even thousand kilometers. It has been found that responses and traces of ruptures occurred before some earthquakes. Therefore it is possible to detect the initial micro ruptures and the dynamic processes of rupture chain generation through observations on the surface or in deep wells. This is probably an important approach to realize short‐term and impeding earthquake prediction.

GPS monitoring and earthquake prediction: A success story towards a useful integration

We describe a success story at the junction between South-Eastern Alps and external Dinarides that has led to an early deployment of GPS stations prior to the predicted July 12th 2004 moderate size Slovenia Krn Mountain earthquake. The success story consisted in a straightforward integration between a long-lasting lithosphere-scale rock mechanics experiment, along with GPS monitoring, leading to a physical model of stress evolution and tested earthquake prediction experiment using M8S, CN and RTP algorithms to point out the area of the impending earthquake. Within the alarmed area by the prediction algorithms, the lithosphere-scale rock mechanics experiment revealed that the location of the 2004 event falls within an area of stress shadow due to the recent 1998 Bovec earthquake, but is also very close to an area of increased stress due to the long-lasting effect of the 1511 event. The pre and post 2004 earthquake GPS data provided the following results: 1- the Krn Mountain earthquake magnitude has to be increased from M W 5.2 to 5.5, therefore doubling the fault slip in order to provide a better fit to the near-field displacements. Accordingly the RTP 2004 alarm in Northern Dinarides can be considered a successful prediction now that the magnitude is inside the prediction range. 2- the existence of an important amount of aseismic deformation related to such a moderate size earthquake and the feasibility of monitoring these transients; 3- the evidence of a resolved acceleration of the strain rates one year prior to the earthquake; 4- the robustness of the Bayesian approach in detecting discontinuities in the times series, their magnitude and statistical significance. The discontinuities or jumps in the time series can correspond to coseismic deformation or time-dependent deformation such as creeping, slow motion, strain acceleration and transients in general; 5- when integrated with tested earthquake prediction algorithms, the capability to forecast earthquakes can be extended to the scale of the active fault systems.

Shear‐wave splitting and earthquake forecasting

AbstractSeismic shear‐wave splitting (SWS) monitors the low‐level deformation of fluid‐saturated microcracked rock. We report evidence of systematic SWS changes, recorded above small earthquakes, monitoring the accumulation of stress before earthquakes that allows the time and magnitude of impending large earthquakes to be stress‐forecast. The effects have been seen with hindsight before some 15 earthquakes ranging in magnitude from an M1.7 seismic swarm event in Iceland to the Ms7.7 Chi‐Chi Earthquake in Taiwan, including a successfully stress‐forecast of a M5.0 earthquake in SW Iceland. Characteristic increases in SWS time‐delays are observed before large earthquakes, which abruptly change to deceases shortly before the earthquake occurs. There is a linear relationship between magnitudes and logarithms of durations of both increases and decreases in SWS time‐delays before large impending earthquakes. However, suitably persistent swarms of small earthquakes are too scarce for routine stress‐forecasting. Reliable forecasting requires controlled‐source cross‐hole seismics between neighbouring boreholes in stress‐monitoring sites (SMS). It would be possible to stress‐forecast damaging earthquakes worldwide by a global network of SMS in real time.

Statistical analysis on yearly seismic moment release data to demarcate the source zone for an impending earthquake in the Himalaya

Tectonism in the Himalayan fold-thrust belt had generated great earthquakes in the past and will spawn more in the future. Sequential cumulative moment release data of macroearthquakes (Mb ≥ 4.5) over the years 1964-2006 in four zones of the Himalaya was analysed by nonparametric RUD method. The Z values of RUD analysis had neither rejected nor supported the null hypothesis of randomness. However, the Hurst analysis and plot, a statistical procedure to identify clustering of low and high values in a time series, brought out a pattern for earthquake prognostication. The pattern was a negative sloping segment representing a sluggish moment release over years, followed by a positive sloping segment indicating a sudden high moment release with occurrence of medium/large size earthquake(s). In recent past, such a negative sloping has been found in Zones B (1992-2006) and D (1998-2006), indicating an impending moderate/mega earthquake event in near future.

Error propagation in time-dependent probability of occurrence for characteristic earthquakes in Italy

Time-dependent models for seismic hazard and earthquake probabilities are at the leading edge of research nowadays. In the framework of a 2-year national Italian project (2005–2007), we have applied the Brownian passage time (BPT) renewal model to the recently released Database of Individual Seismogenic Sources (DISS) to compute earthquake probability in the period 2007–2036. Observed interevent times on faults in Italy are absolutely insufficient to characterize the recurrence time. We, therefore, derived mean recurrence intervals indirectly. To estimate the uncertainty of the results, we resorted to the theory of error propagation with respect to the main parameters: magnitude and slip rate. The main issue concerned the high variability of slip rate, which could hardly be reduced by exploiting geodetic constraints. We did some validation tests, and interesting considerations were derived from seismic moment budgeting on the historical earthquake catalog. In a time-dependent perspective, i.e., when the date of the last event is known, only 10–15% of the 115 sources exhibit a probability of a characteristic earthquake in the next 30 years higher than the equivalent Poissonian probabilities. If we accept the Japanese conventional choice of probability threshold greater than 3% in 30 years to define “highly probable sources,” mainly intermediate earthquake faults with characteristic M < 6, having an elapsed time of 0.7–1.2 times the recurrence interval are the most “prone” sources. The number of highly probable sources rises by increasing the aperiodicity coefficient (from 14 sources in the case of variable α ranging between 0.22 and 0.36 to 31 sources out of 115 in the case of an α value fixed at 0.7). On the other hand, in stationary time-independent approaches, more than two thirds of all sources are considered probabilistically prone to an impending earthquake. The performed tests show the influence of the variability of the aperiodicity factor in the BPT renewal model on the absolute probability values. However, the influence on the relative ranking of sources is small. Future developments should give priority to a more accurate determination of the date of the last seismic event for a few seismogenic sources of the DISS catalog and to a careful check on the applicability of a purely characteristic model.

The Prediction of Two Large Earthquakes in Greece

The VAN experimental method of shortterm earthquake prediction (named after the initials of three Greek physicists, Panayiotis Varotsos, Kessar Alexopoulos, and Konstantine Nomicos) has been used to monitor preseismic electric signals since the 1980s [see Varotsos, 2005]. From observed telluric current signals, called seismic electric signals (SES), the epicentral area, magnitude, and occurrence time of an impending earthquake are estimated. SES are interpreted as having been emitted when the focal region in which the earthquake in question could occur has entered the critical regime (i.e., a stage close to the rupture).The VAN method recently reached the stage of possibly enabling the narrowing of the time window of earthquake prediction to the order of a few days. This narrowing is made possible by the use of a new method called “natural time analysis.” This analysis has been developed to identify the time when a dynamic system (i.e., a system evolving with time) exhibits behavior similar to a phase change [Varotsos et al., 2008, and references therein]. On the hypothesis that the main shock earthquake is a critical phenomenon, when SES activity is observed, natural time analysis is conducted on the seismicities of small earthquakes in the suspected future epicentral area solely by considering their order of occurrence and the energy emitted by each of them. The term natural time analysis stems from the disregard of the conventional time of the earthquakes' occurrence. It has been found that such an analysis enables the identification of the time of the main shock usually within a few days before it occurs (see P. Varotsos et al., Seismic electric signals and 1/f “noise” in natural time, at http://arxiv.org/abs/ 0711.3766).

Analysis of seismoionospheric disturbances at the Chain of Japanese stations for vertical sounding of the ionosphere

Seismoionospheric disturbances in the parameters of the ionospheric F2 and sporadic E layers at the chain of the Japanese stations for vertical sounding of the ionosphere before strong crustal earthquakes with M>6.5 during the period from 1968 to 1992 have been considered. The dependence of the disturbance time of appearance in the ionospheric parameters on the earthquake magnitude and epicentral distance, obtained for each specific earthquake using the selected series of ionospheric stations, made it possible to consider these disturbances among medium-term precursors of earthquakes. The velocity of the disturbance front apparent motion has been determined based on the model of horizontal radially-isotropic disturbance propagation from the projection of the impending earthquake epicenter to the ionospheric altitudes. The conclusion has been made that the distinguished seismoionospheric disturbances follow the boundary of the earthquake preparation region, expanding on the Earth’s surface.

Soil-gas radon as seismotectonic indicator in Garhwal Himalaya

Research on earthquake-related radon monitoring has received enormous attention recently. Anomalous behaviour of radon in soil and groundwater can be used as a reliable precursor for an impending earthquake. While earthquake prediction may not yet be possible, earthquake prediction research has greatly increased our understanding of earthquake source mechanisms, the structural complexities of fault zones, and the earthquake recurrence interval, expected at a given location. This paper presents some results of continuous monitoring of radon in soil-gas in Garhwal Himalaya, India. Daily soil-gas radon monitoring with seismic activity and meteorological parameters were performed in the same laboratory system, located at H.N.B. Garhwal University Campus, Tehri Garhwal, India. Radon anomalies along with meteorological parameters were found to be statistically significant for the seismic events within the magnitudes M2.0-M6.0 and epicentral distances of 16–250 km from the monitoring station. The frequent positive and negative anomalies with constant environmental perturbation indicate the opening and closing of micro cracks within the volume of dilatancy by strain energy. The spike-like and sharp peak anomalies were recorded before, during and after earthquakes occurred in the area. The variations in radon concentrations in soil-gas are found to be correlated with seismic activities in the Garhwal Himalaya. The correlation between radon level and meteorological parameters is also discussed.

Satellite detection of earthquake thermal infrared precursors in Iran

Stress accumulated in rocks in tectonically active areas may manifest itself as electromagnetic radiation emission and temperature variation through a process of energy transformation. Land surface temperature (LST) changes before an impending earthquake can be detected with thermal infrared (TIR) sensors such as NOAA-AVHRR, Terra/Aqua-MODIS, etc. TIR anomalies produced by 10 recent earthquakes in Iran during the period of Jun 2002–Jun 2006 in the tectonically active belt have been studied using pre- and post-earthquake NOAA-AVHRR datasets. Data analysis revealed a transient TIR rise in LST ranging 2–13°C in and around epicentral areas. The thermal anomalies started developing about 1–10 days prior to the main event depending upon the magnitude and focal depth, and disappeared after the main shock. In the case of moderate earthquakes (<6 magnitude) a dual thermal peak instead of the single rise has been observed. This may lead us to understand that perhaps pre-event sporadic release of energy from stressed rocks leads to a reduction in magnitude of the main shock. This TIR temperature increment prior to an impending earthquake can be attributed to degassing from rocks under stress or to p-hole activation in the stressed rock volume and their further recombination at the rock–air interface. A precise correlation of LST maps of Bam and Zarand with InSAR-generated deformation maps also provides evidence that the thermal anomaly is a ground-related phenomenon, not an atmospheric one.

Stress-forecasting (not predicting) earthquakes: A paradigm shift

After 120 years of unsuccessful endeavor, a paradigm shift is required before earthquakes can be predicted. The most sensitive diagnostic of low-level changes of stress in in situ rock, variations in microcrack geometry, can be monitored by analyzing shear-wave splitting. The suggested paradigm shift is that, instead of investigating the source zone, we monitor stress accumulation before earthquakes at, possibly, substantial distances from the source. Characteristic temporal variations of shear-wave time delays have been observed in retrospect before 14 earthquakes worldwide. On one occasion, when changes were recognized early enough, the time, magnitude, and fault break of an M = 5 earthquake in southwest Iceland were successfully stress-forecast in a narrow time-magnitude window. Such stress accumulation can be theoretically modeled and is believed to be at least partially understood. When sufficient shear-wave source earthquakes are available, increasing time delays also show an abrupt decrease shortly before the impending earthquake occurs. This is not fully understood but is thought to be caused by stress relaxation as microcracks coalesce onto the eventual fault break. The new result confirming these ideas, and justifying the paradigm shift, is that logarithms of the durations of both increases and decreases in time delays are found to be proportional (self-similar) to the magnitudes of impending earthquakes.

Dynamical complexity detection in pre-seismic emissions using nonadditive Tsallis entropy

We investigate, within the framework of nonextensive Tsallis entropy, particular aspects of the relation between signal analysis and signals originating in a very special nonlinear system: the focal area of an impending earthquake. The Tsallis-like time-dependent entropy is shown to be a rather powerful tool for providing a novel quantitative strategy for monitoring the focal area states just before the earthquake occurrence.

Characteristics of VHF over-horizon signals possibly related to impending earthquakes and a mechanism of seismo-atmospheric perturbations

There have been evidences of the presence of atmospheric disturbances associated with earthquakes, as based on the reception of over-horizon VHF signals. In this paper we propose a generation mechanism of such atmospheric perturbation based on the changes in geochemical quantities associated with earthquakes.

Do Early Tremors Give Sneak Preview of Quake's Power?

SEISMOLOGYItalian researchers say the same waves used to predict impending earthquakes can also reveal how strong the tremor will be, allowing a more appropriate disaster response. But some experts are skeptical. ([Read more][1].) [1]: http://www.sciencemag.org/cgi/content/full/314/5806/1670

Multi-seismic cycle velocity and strain fields for an active normal fault system, central Italy

Vertical offsets of Late Pleistocene–Holocene deposits and landforms are combined with slip-direction indicators on dipping active normal faults in central Italy to produce velocity and strain-rate fields averaged since 12–18 ka for a 5 by 5 km grid. Maximum strain-rates of 0.078 ± 0.0156 ppm/yr, or 0.052 ± 0.01 ppm/yr across a distance of 63,639 m imply maximum NE–SW extension rates of 5.0 ± 1.0 mm/yr or 3.3 ± 0.66 mm/yr depending on whether rates are averaged over 12 ka or 18 ka. The high spatial resolution reveals that strain-rates vary by up to 0.04 ± 0.008 or 0.06 ± 0.012 ppm/yr over a distance of only c. 7 km along the strike of the fault system, again depending on the timescale chosen. For the first time, these data allow a comparison of rates derived over time periods that would contain numerous seismic cycles with those measured with GPS that represent either interseismic strain, or displacements due to a single large earthquake with some interseismic strain. Overall, the rates compare reasonably well with those measured geodetically or derived from seismic moment summations (< 0.12 ppm/yr and generally in the range of 0.10–0.06 ppm/yr; 6.36–3.82 mm/yr). However, the present wide spacing of geodetic sites (30–40 km) means that the small-scale spatial variations in strain-rate since 12–18 ka have not yet been resolved using GPS. This makes it difficult to compare strain measured geodetically with that released during historical earthquakes to assess whether excess strain will be released in an impending earthquake.

A stress-forecast earthquake (with hindsight), where migration of source earthquakes causes anomalies in shear-wave polarisations

The stress-aligned shear-wave splitting observed throughout most of the crust is a three-dimensional function of the effective elastic anisotropy of distributions of fluid-saturated grain-boundary cracks and preferentially oriented pores. Fluid-saturated microcracks are highly compliant and crack geometry responds readily to changes in stress. Monitoring with shear-wave splitting allows the accumulation of stress before earthquakes to be recognised and the time and magnitude of the impending earthquake to be stress-forecast. Such increases in stress have been observed some 15 times with hindsight and one successful real-time stress-forecast. Here we report a further with-hindsight stress-forecast in Northern Iceland, where increases of time-delays implying stress accumulation are observed before a 4.9 earthquake at two seismic stations at epicentral distances of 50 km and 92 km. There are, however, two anomalies. Changes in shear-wave polarisations at the nearest station appear to be due to migration of shear-wave source earthquakes, in a uniform anisotropic symmetry, into ray path directions with different anisotropic shear-wave polarisations. Such directional changes in shear-wave polarisations are occasionally observed above small earthquakes and may be misinterpreted as structural or temporal changes in anisotropy. A further anomaly is that the station at 92 km displays variations in time-delays, but a station just 4 km farther away on the other side of a major fault appears to be in the stress shadow of the fault and does not display temporal variations despite having adequate source data.

Gradients and phase velocities of ULF geomagnetic disturbances used to determine the source of an impending strong earthquake

Results of studying the behavior of the vectors of gradients and phase velocities of ULF geomagnetic disturbances (F 5), the values of gradients and phase velocities start anomalously changing, and directions toward sources of impending strong earthquakes appear in the distribution of gradient vector directions. Directions from sources of impending earthquakes appear in the distribution of phase velocity vector directions. It is proposed to use gradients and phase velocities of ULF and ELF geomagnetic disturbances as one of the factors in a short-term prediction of strong earthquakes.

Surface latent heat flux and nighttime LF anomalies prior to the M&amp;lt;sub&amp;gt;w&amp;lt;/sub&amp;gt;=8.3 Tokachi-Oki earthquake

Abstract. Surface Latent Heat Flux (SLHF) is an atmospheric parameter proportional to the evaporation from the Earth's surface. SLHF has been found to exhibit an anomalous behavior in the epicentral region prior to several coastal earthquakes. Sub-ionospheric low frequency (LF) radio sounding measurements have shown its potentiality for the short-term earthquake forecasting since the last decade. The anomalous SLHF and nighttime LF sub-ionospheric signals are found to show complementary nature associated with the large Tokachi-Oki earthquake of 25 September 2003. Such complementary nature of parameters may prove to be potential in providing early warning information about an impending earthquake.