Efficiency of earthquake forecast models based on earth tidal correlation with background seismicity along the Tonga–Kermadec trench

The correlation between Earth’s tides and background seismicity has been suggested to become stronger before great earthquakes and weaker after. However, previous studies have only retrospectively analyzed this correlation after individual large earthquakes; it thus remains vague (i) whether such variations might be expected preceding future large earthquakes, and (ii) the strength of the tidal correlation during interseismic periods. Therefore, we retrospectively investigated whether significant temporal variations of the tidal correlation precede large interplate earthquakes along the Tonga–Kermadec trench, where Mw 7-class earthquakes frequently occurred from 1977 to 31 December 2020. We evaluated a forecast model based on the temporal variations of the tidal correlation via Molchan’s error diagram, using the tidal correlation value itself as well as its rate of change as threshold values. For Mw ≥ 7.0 earthquakes, this model was as ineffective as random guessing. For Mw ≥ 6.5, 6.0, or 5.5 earthquakes, the forecast model performed better than random guessing in some cases, but even the best forecast only had a probability gain of about 1.7. Therefore, the practicality of this model alone is poor, at least in this region. These results suggest that changes of the tidal correlation are not reliable indicators of large earthquakes along the Tonga–Kermadec trench. Graphical Abstract

How Good is a Paleoseismic Record of Megathrust Earthquakes for Probabilistic Forecasting?

Time-dependent earthquake forecast depends on the frequency and number of past events and time since the last event. Unfortunately, only a few past events are historically documented along subduction zones where forecasting relies mostly on paleoseismic catalogs. We address the role of dating uncertainty and completeness of paleoseismic catalogs on probabilistic estimates of forthcoming earthquakes using a 3.6-ka-long catalog including 11 paleoseismic and 1 historic (Mw≥8.6) earthquakes that preceded the great 1960 Chile earthquake. We set the clock to 1940 and estimate the conditional probability of a future event using five different recurrence models. We find that the Weibull model predicts the highest forecasting probabilities of 44% and 72% in the next 50 and 100 yr, respectively. Uncertainties in earthquake chronologies due to missing events and dating uncertainties may produce changes in forecast probabilities of up to 50%. Our study provides a framework to use paleoseismic records in seismic hazard assessments including epistemic uncertainties.

Geo-Chemical Techniques for Earthquake Forecasting in Nigeria

Regardless of the doubt caused by some rounds on the impossibility of earthquake forecast, more and more countries, even at the highest governmental levels, realize that doing nothing is the ostrich position of dread before the real difficulties associated with the creation of a real forecasting system. Nigeria in times past was believed to be aseismic. However, the seismic record of Nigeria from 1933-2021 have demonstrated in contrast to the idea, numerous quakes have been recorded in Nigeria throughout the years. With the development of observation techniques and theoretical knowledge of geochemistry, geochemical observation of faults gas has become a hotspot once more in recent years. Rn, Hg, H2, etc., are used for geochemical observations. 222Rn has a half-life of 3.825 days, a magnitude 5.0 earthquake will be detected through precursory phenomena at a distance not greater than 142 km. Mercury and other elements are used as important detectors for earthquake prediction and they play an important role in revealing the relationship between fluid in the fault zone and the occurrence of earthquakes, the range for a magnitude 5.0 earthquake is limited to 200 km. Hydrogen concentrations have been monitored for precursory variations in many fault systems, using either discrete sampling and laboratory analysis or continuous monitoring of ground gas, using hydrogen-sensitive fuel cells. Precursory changes in groundwater chemistry are often attributed to the mixing of fluids from two or more chemically distinct aquifers, the physical mechanism responsible for the mixing of fluids is, however, not well established.

Assessing Earthquake Forecast Performance Based on b Value in Yunnan Province, China

Many studies have shown that b values tend to decrease prior to large earthquakes. To evaluate the forecast information in b value variations, we conduct a systematic assessment in Yunnan Province, China, where the seismicity is intense and moderate–large earthquakes occur frequently. The catalog in the past two decades is divided into four time periods (January 2000–December 2004, January 2005–December 2009, January 2010–December 2014, and January 2015–December 2019). The spatial b values are calculated for each 5-year span and then are used to forecast moderate-large earthquakes (M ≥ 5.0) in the subsequent period. As the fault systems in Yunnan Province are complex, to avoid possible biases in b value computation caused by different faulting regimes when using the grid search, the hierarchical space–time point-process models (HIST-PPM) proposed by Ogata are utilized to estimate spatial b values in this study. The forecast performance is tested by Molchan error diagram (MED) and the efficiency is quantified by probability gain (PG) and probability difference (PD). It is found that moderate–large earthquakes are more likely to occur in low b regions. The MED analysis shows that there is considerable precursory information in spatial b values and the forecast efficiency increases with magnitude in the Yunnan Province. These results suggest that the b value might be useful in middle- and long-term earthquake forecasts in the study area.

Ionosphere Sounding for Pre-seismic Anomalies Identification (INSPIRE): Results of the Project and Perspectives for the Short-Term Earthquake Forecast

The INSPIRE project was dedicated to the study of physical processes and their effects in ionosphere which could be determined as earthquake precursors together with detailed description of the methodology of ionospheric pre-seismic anomalies definition. It was initiated by ESA and carried out by an international consortium. The full set of key parameters of the ionospheric plasma was selected based on the retrospective analysis of the ground-based and satellite measurements of pre-seismic anomalies. Using this classification the multi-instrumental database of worldwide relevant ionospheric measurements (ionosonde and GNSS networks, LEO-satellites with in situ probes including DEMETER and FORMOSAT/COSMIC ROC missions) was developed for the time intervals related to selected test cases. As statistical processing shows, the main ionospheric precursors appear approximately 5 days before the earthquake within the time interval of 30 days before and 15 days after an earthquake event. The physical mechanisms of the ionospheric pre-seismic anomalies generation from ground to the ionosphere altitudes were formulated within framework of the Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) model. The processes of precursor’s development were analyzed starting from the crustal movements, radon emission and air ionization, thermal and atmospheric anomalies, electric field and electromagnetic emissions generation, variations of the ionospheric plasma parameters, in particular vertical TEC and vertical profiles of the electron concentration. The assessment of the LAIC model performance with definition of performance criteria for earthquake forecasting probability has been done in statistical and numerical simulation domains of the Global Electric Circuit. The numerical simulations of the earthquake preparation process as an open complex system from start of the final stage of earthquake preparation up to the final point–main shock confirms that in the temporal domain the ionospheric precursors are one of the most late in the sequence of precursors. The general algorithm for the identification of the ionospheric precursors was formalized which also takes into account the external Space Weather factors able to generate the false alarms. The importance of the special stable pattern called the “precursor mask” was highlighted which is based on self-similarity of pre-seismic ionospheric variations. The role of expert decision in pre-seismic anomalies interpretation for generation of seismic warning is important as well. The algorithm performance of the LAIC seismo-ionospheric effect detection module has been demonstrated using the L’Aquila 2009 earthquake as a case study. The results of INSPIRE project have demonstrated that the ionospheric anomalies registered before the strong earthquakes could be used as reliable precursors. The detailed classification of the pre-seismic anomalies was presented in different regions of the ionosphere and signatures of the pre-seismic anomalies as detected by ground and satellite based instruments were described what clarified methodology of the precursor’s identification from ionospheric multi-instrumental measurements. Configuration for the dedicated multi-observation experiment and satellite payload was proposed for the future implementation of the INSPIRE project results. In this regard the multi-instrument set can be divided into two groups: space equipment and ground-based support, which could be used for real-time monitoring. Together with scientific and technical tasks the set of political, logistic and administrative problems (including certification of approaches by seismological community, juridical procedures by the governmental authorities) should be resolved for the real earthquake forecast effectuation.

Short-term earthquake forecast

In the manuscript, a tectonomagnetic model of forming the source zone of a strong earthquake is presented from the position of the electromagnetic field of Earth. The model is based on the idea of magnetic interaction between geological blocks screening, when the bond to each other by adhesion, a flux of abyssal fluids with the formation of a seismogenic structure. The source zone of strong earthquakes formed inside the seismogenic structure is followed by the development of an anomalous electromagnetic field. The existence of the deterministic cause-and-effect relationship between anomalous electromagnetic field inside the formed earthquake source and a change in atmospheric pressure determines the possibilities of conducting short-term prediction of time, place, and force of the earthquake. Registration of the earthquake source zone by barometric method during hydrogeodynamic monitoring makes it possible to make short-term predictions of it by time, place, and force. The substantiation and examples are given for short-term prediction of time, geographical location, and force of strong earthquakes in basic seismically active regions of Russia.

Обоснование основных положений деформационной модели подготовки очага корового землетрясения

The article reasonably shows that the uppermost layer of the Earth's crust up to 25 kilometers is seismogenic. Aim. The article provides the evidence that crustal seismicity is generated not by regional stress fields of a homogeneous shear, as it was adopted in the strategy for solving the problem of earthquake forecast, but by local fields of exponential elastic stress. Such fields arise in one or another section of a seismogenic fault due to the occurrence of a stress concentrator in this section. According to the Saint Venant principle, such a stress concentrator (an additional load in the system) generates a local stress field of an exponential form. In this field the maximum stress is localized in the areas of an increment load application (in the fault) and decreases very quickly (exponentially) on both sides of the fault. Such stress concentrators arise in those areas of a seismogenic fault, where displacements along the fault stop due to various reasons. G.A. Gamburtsev foresaw this situation and very precisely called such concentrators as “seams”. The origin of a local stress field at the place, where a seam appears, is caused by the following fact: the power impulse generated by the seam is small compared to the linear momentum of the entire system of blocks of the considered fault and, therefore, it will stop the displacement of blocks only within the seam; but the displacements of blocks outside the seam will continue in the same mode. One can single out the following reasons causing stress concentrators in the fault: variations in different stress fields, changing the value of the friction coefficient in the fault; variations in fluid processes; the influence of temperature and pressure; mechanical “hooks” of blocks due to irregularities of their contacting surfaces, etc. Methods. The fact of the existence of the considered local stress fields is confirmed by geodetic studies, i.e. the results of repeated geodetic measurements in the epicentral zones of strong earthquakes. Results.These results allow drawing the following conclusions: 1) the sign of the preparation of a crustal earthquake source was reliably determined. This sign means the increasing deformation of the elastic bending of rocks in the source in the course of time; 2) from the standpoint of solving the problem of earthquake forecast, the main and decisive result of these studies is that the deformation processes occurring in the impending source also capture the Earth's surface, because this is precisely what opens up great opportunities in solving this problem; 3) with the help of special geodetic systems (forecast profiles), one can detect the places of the impending earthquake source preparation, i.e. make an accurate forecast of the site of a future earthquake; 4) since the energy of the earthquake source is functionally related to its size, one can realize the correct prediction of the maximum possible intensity of the future earthquake by determining the length of the seismogenic fault section, elastically deformed by the preparation of the earthquake using the forecast profiles В статье обоснованно показано, что сейсмогенным является самый верхний слой земной коры мощностью до 25 километров. Цель работы. В статье приведены доказательства того, что коровая сейсмичность порождается вовсе не региональными полями напряжений однородного сдвига, как это было принято в стратегии решения проблемы прогноза землетрясений, а локальными полями упругих напряжений экспоненциального вида. Такие поля возникают в том или ином участке сейсмогенного разлома из-за появления на этом участке концентратора напряжений. Согласно принципу Сен-Венана такой концентратор напряжений (дополнительная нагрузка в системе) порождает локальное поле напряжений экспоненциального вида. Максимальная величина напряжения в этом поле расположена в месте приложения дополнительной нагрузки (в разломе) и очень быстро (экспоненциально) убывает в обе стороны от разлома. Такие концентраторы напряжений возникают на тех участках сейсмогенного разлома, на которых в силу тех или иных причин прекращаются смещения по разлому. Г.А. Гамбурцев провидчески предвидел данную ситуацию и очень метко такие концентраторы назвал «спайками»». Возникновение локального поля напряжений в месте появления спайки обусловлено тем, что импульс силы, порождаемый спайкой мал по сравнению с количеством движения всей системы блоков рассматриваемого разлома и, следовательно, он остановит смещение блоков лишь в пределах спайки, но смещения блоков вне спайки будут продолжаться в прежнем режиме. Среди причин, порождающих концентраторы напряжений в разломе можно назвать следующие: вариации различных полей напряжений, изменяющие величину коэффициента трения в разломе; влияние температуры и давления; вариации флюидных процессов; механические «зацепы» блоков из-за неровностей их соприкасающихся поверхностей и др. Методы исследования. Факт существования рассматриваемых локальных полей напряжений подтвержден геодезическими исследованиями – результатами повторных геодезических измерений в эпицентральных зонах сильных землетрясений. Результаты работы. Эти результаты позволяют сделать следующие выводы: 1) достоверно определен признак подготовки очага корового землетрясения, которым является нарастающая во времени деформация упругого изгиба горных пород в его очаге; 2) с позиций решения проблемы прогноза землетрясений главным и определяющим результатом этих исследований является то, что происходящие в готовящемся очаге деформационные процессы захватывают и земную поверхность, ибо именно это открывает большие возможности в решении этой проблемы; 3) с помощью специальных геодезических систем (прогнозных профилей) можно обнаруживать места подготовки очагов готовящихся землетрясений, т.е. осуществлять точный прогноз места будущего землетрясения; 4) так как энергия очага землетрясения функционально связана с его размерами, то определив с помощью прогнозных профилей длину участка сейсмогенного разлома, упруго деформированного подготовкой землетрясения, можно осуществить и точный прогноз максимально возможной силы будущего землетрясения

Ionospheric precursors of earthquakes from satellites

<p>In-situ magnetic field and electron density, as observed by Swarm and CSES satellites, are analyzed to identify possible anomalies in geomagnetic quiet time with respect to the ionospheric background. To avoid detecting possible anomalies induced by auroral activity we investigate regions between +50 and -50 degrees in magnetic latitude. Then a superposed epoch and space approach is applied to this anomaly dataset with respect to their time and space distance from shallow M5.5+ earthquakes occurred in about last 6 years. A comparison with analogous homogeneous random distribution of anomalies shows that the real anomaly concentrations found before the occurrence of earthquakes are statistically significant. In addition, we find that, in general, the anticipation times of the ionospheric precursors scale with the earthquake magnitude, confirming the validity of the Rikitake law for ionospheric signals, previously valid for ground precursors. We also find that the anomaly duration seems to depend on the magnitude of the impending earthquake. Finally, we propose a simple scheme of potential earthquake forecast on the base of the previously mentioned characteristics.</p>