German Seismic and Infrasound Networks Contributing to the European Integrated Data Archive (EIDA)

Germany has a long history in seismic instrumentation. The installation of the first station sites was initiated in those regions with seismic activity. Later on, with an increasing need for seismic hazard assessment, seismological state services were established over the course of several decades, using heterogeneous technology. In parallel, scientific research and international cooperation projects triggered the establishment of institutional and nationwide networks and arrays also focusing on topics other than monitoring local or regional areas, such as recording global seismicity or verification of the compliance with the Comprehensive Nuclear-Test-Ban Treaty. At each of the observatories and data centers, an extensive analysis of the recordings is performed providing high-level data products, for example, earthquake catalogs, as a base for supporting state or federal authorities, to inform the public on topics related to seismology, and for information transfer to international institutions. These data products are usually also accessible at websites of the responsible organizations. The establishment of the European Integrated Data Archive (EIDA) led to a consolidation of existing waveform data exchange mechanisms and their definition as standards in Europe, along with a harmonization of the applied data quality assurance procedures. In Germany, the German Regional Seismic Network as national backbone network and the state networks of Saxony, Saxony-Anhalt, Thuringia, and Bavaria spearheaded the national contributions to EIDA. The benefits of EIDA are attracting additional state and university networks, which are about to join the EIDA community now.

The global seismic activity influence on process in atmosphere and ionosphere

In recent decades, ideas about earthquakes (EQ) have been formed as a final stage of a planetary continuous self-organizing tectonic process with periods of accumulation and relaxation of tectonic stresses. However, the scientific literature still presents studies of the response of atmospheric and ionospheric processes to individual strong EQs. In this paper, for the first time, the relationship between processes in the lithosphere, troposphere, and ionosphere is considered, taking into account new ideas about the seismic process as a global phenomenon and on the background of processes caused by space weather. Both planetary data (EQ, total electron content (TEC) of the ionosphere) and data (atmospheric pressure, critical frequency of the F2 layer of the ionosphere) of widely spaced observation points in the western and eastern hemispheres were used. To increase the reliability of statistical results, 4 independent databases of daily data for 2007–2015 were used. Stable effects of global seismic activity (GSA) in the considered parameters are established. Thus, the critical frequency of the F2 region with a sharp increase in the GSA increases by 0.4–0.5 MHz. This effect is quite stable and manifests itself almost simultaneously at ionospheric stations of the eastern and western hemispheres, as well as in planetary TEC values. At the same time, in the ionospheric variations, as before, the influence of both the troposphere (especially at a low level of solar activity) and space weather is traced, the characteristics of which in 75 % of cases also show an association with GSA. Therefore, space weather often but not always can act as a trigger on the EQs. In general, in the western hemisphere, the minimum atmospheric pressure occurs earlier than in the eastern, which leads to a noticeable increase in the pressure difference between the hemispheres by 10 mm. Hg., that indicates the relationship between global seismicity and global atmospheric circulation. The established GSA effects, as a rule, have the character of not a local short-term burst, but a jump followed by a gradual decrease (increase) of the index until the next active period (saw-toothed curve), i.e., the influence of the lithosphere on the overlying layers is continuous and is cyclical in nature, probably due to the cyclical nature of tectonic processes. Most likely, several different couplings between geospheres are realized at the same time, partially synchronized by changes in space weather, which requires new physical mechanisms to explain them.

Geological and Geophysical Factors Constraining the Occurrence of Earthquake Precursors in Geofluids: A Review and Reinterpretation

In this paper, we update the previous compilations of observed earthquake precursors from the published scientific literature of the last decade. We collected the epicentral coordinates, magnitude, hypocentral depth of each earthquake and the distance from the observed precursor and its time lag. The locations are reported and compared with data concerning geological and geophysical parameters like global seismicity, volcanic locations, heat flow and tectonic regimes. Possible relations between geological and geophysical parameters and the occurrence of fluid-related earthquake precursors are considered and discussed. Some geological and geophysical conditions can be deemed responsible for the occurrence of fluid-related earthquake precursory phenomena. Geophysical models used to explain the occurrence of earthquake precursors are discussed with the purpose of contributing to engineering proper monitoring networks. Areas of the world potentially suitable for earthquake fluid-related precursor monitoring are suggested.

GLOBAL EARTHQUAKES

The information on global seismicity in 2014 at the level of strong earthquakes with M≥6 according to the Seismological Bulletin of the Geophysical Survey of RAS (GS RAS) is provided. The original Seismological Bulletin for 2014 contains parameters of 3268 earthquakes in the world, versus 4212 in 2013. This article analyzes 165 earthquakes with M≥6, including 16 strongest earthquakes with M≥7, and five earthquakes with M6.0–6.7, which resulted in significant casualties and destruction. The information on focal mechanisms, macroseismic effect, the number of victims, tsunamis, etc. is given. A comparative analysis of the number of earthquakes and released seismic energy in different seismically active regions of the Earth showed that, as before, the Pacific region was the most seismically active. More than 96 % of common seismic energy was re-leased in the Pacific region, compared to 1.8 % in Eurasia, 1.3 % in Atlantic Ocean and 0.2 % in the Indian Ocean. The Earth’s maximum earthquake in 2014 occurred on April 1 with Mw=8.1 off shore of Chile. It was accompanied by numerous foreshocks and aftershocks. The maximum casualties and material damage in 2014 were caused by the catastrophic Ludian earthquake that occurred on August 3 with MS=6.2 in the Chinese province of Yunnan.

Two global ensemble seismicity models obtained from the combination of interseismic strain measurements and earthquake-catalogue information

SUMMARY Global seismicity models provide scientific hypotheses about the rate, location and magnitude of future earthquakes to occur worldwide. Given the aleatory variability of earthquake activity and epistemic uncertainties in seismicity forecasting, the veracity of these hypotheses can only be confirmed or rejected after prospective forecast evaluation. In this study, we present the construction of and test results for two updated global earthquake models, aimed at providing mean estimates of shallow (d ≤ 70 km) seismicity for seismic hazard assessment. These approaches, referred to as the Tectonic Earthquake Activity Model (TEAM) and the World Hybrid Earthquake Estimates based on Likelihood scores (WHEEL) model, use the Subduction Megathrust Earthquake Rate Forecast (SMERF2), an earthquake-rate model for subduction zones constrained by geodetic strain measurements and earthquake-catalogue information. Thus, these global ensemble seismicity models capture two independent components necessary for long-term earthquake forecasting, namely interseismic crustal strain accumulation and sudden lithospheric stress release. The calibration period for TEAM and WHEEL extends from 1977 January 1 to 2013 December 31. Accordingly, we use m ≥ 5.95 earthquakes recorded during the 2014–2019 period to pseudo-prospectively evaluate the forecasting skills of these earthquake models, and statistically compare their performances to that of the Global Earthquake Activity Rate (GEAR1) model. As a result, GEAR1 and WHEEL are the most informative global seismicity models during the pseudo-prospective test period, as both rank with the highest information scores among all participant earthquake-rate forecasts. Nonetheless, further prospective evaluations are required to more accurately assess the abilities of these global ensemble seismicity models to forecast long-term earthquake activity.