Gheorghe Marmureanu

An Early Warning System for Deep Vrancea (Romania) Earthquakes

Nowadays natural disasters phenomena as hurricanes, volcanic eruptions, tsunamis or earthquakes, are still difficult to prevent. Based on signaling of the phenomenon appearance in the destructive area, important human losses and material damages are avoided. For that reason, WARNING turns into a key objective, both in theoretical and practical research.

Estimation of site effects in Bucharest caused by the May 30-31, 1990, Vrancea seismic events

Abstract. The Vrancea region seismicity, characterized by focal depths larger than 60 km and major events with magnitudes Mw≥ 6.9, is responsible for the most destructive effects experienced in the Romanian territory, and may seriously affect high risk construction located on a wide area, from Central to Eastern Europe. This seismogenic volume must be taken into account both for seismic hazard analysis at the regional level (southeastern Europe) and national level (Romania and Bulgaria) as well as for microzonation studies of the highly populated cities located in the range of influence of this source. Since about four destructive earthquakes occur every century in Vrancea, the microzonation of Bucharest, the main city exposed to the potential damages due to these strong intermediate-depth shocks, represents an essential step towards the mitigation of the local seismic risk. Two main approaches can be considered for the evaluation of the local seismic hazard: (a) collection and extended use, for engineering purposes, of the recorded strong motion data, and (b) advanced modelling techniques that allow us the computation of a realistic seismic input, which can compensate for the lack of strong motion records, actually available only for a few events that occurred in the last 20–30 years.¶Using a ground motion simulation technique that combines modal summation and finite differences, we analyze, along a geologic profile representative of the Bucharest area, the differences in the expected ground motion when two source mechanisms corresponding to the May 30–31, 1990, intermediate-depth Vrancea earthquakes, typical events for the Vrancea seismogenic zone, are considered. All three components of motion are influenced by the presence of the deep alluvial sediments, the strongest local effect being visible in the transversal (T) one, both observed and computed. The details of the local effects vary with varying the earthquake scenario, R and V components being very sensitive. Therefore, for a reliable determination of the seismic input all three components of motion (R, V and T) should be used.

Historical Earthquakes: New Intensity Data Points Using Complementary Data from Churches and Monasteries

The Vrancea seismogenic zone denotes a peculiar source of seismic hazard which represents a major concern in Europe, especially to Romania and neighbouring regions from Bulgaria, Serbia and Republic of Moldova. The strong seismic events that can occur in this area can generate the most destructive effects in Romania and may affect high-risk manmade structures such as nuclear power plants, chemical plants, large dams and pipelines located within a wide area including the Northern zone from the Republic of Bulgaria and the SW of the Moldavia Republic. A major part of the information for determining the design basis earthquakes consists of a complete set of historical earthquake data. Therefore, it is necessary that the available historical records to be collected, extending as far back in time as possible. Most of these historical records will be of descriptive nature, including such information as the number of houses damaged or destroyed, the behaviour of population etc. But from such information a measure of the intensity scale value of each earthquake in modern macroseismic intensity scale values may be determined. During the past project “Bridging the gap between seismology and earthquake engineering: from the seismicity of Romania towards a refined implementation of seismic action EN1998-1 in earthquake resistant design of buildings (BIGSEES)”, the authors developed the macroseismic intensity map of Romania by using newly compiled information about the damages experienced by 115 churches and monasteries after 10 strong earthquakes (Mw > 6.9) occurred in Vrancea zone starting with XVth century.

Main Characteristics of November 10, 1940 Strong Vrancea Earthquake in Seismological and Physics of Earthquake Terms

Vrancea earthquake on November 10th, 1940 (MW = 7.7; MGR = 7.5; h = 150 km; E = 1.122 × 1023 ergs, Imax = IX½) represents the first large earthquake in the last century and was preceded by other earthquakes as: October 22, 1940 (MW = 6.5) and November 8, 1940 (MW = 5.9). If recorded, it would be given the opportunity to get basic data for seismic hazard assessment and useful conclusions for seismic design of structures to strong earthquakes. Unfortunately, no seismic ground motion was recorded and, as a consequence, no improvements of the Romanian design building code were made after this earthquake. The earthquake of November 10, 1940 confirms the existence of deep earthquakes in Vrancea area, deeper than Moho discontinuity in the lower lithosphere, and this theory was developed for the first time by H. Jeffreys in 1935. Focsani city and several municipalities (Cotesti, Panciu etc.) were almost destroyed and the houses not taller than one floor, were completely damaged. More than 45 churches and monasteries were damages, destroyed or demolished. New data regarding damages at monasteries have been synthesized and analyzed, the resulting intensities are completing the known macroseismic field and data may be used to construct the isoseismic map of the maximum possible Vrancea earthquake.

Rapid Earthquake Early Warning (REWS) in Romania: Application in Real Time for Governmental Authority and Critical Infrastructures

In Romania, there is an operational early warning system that is able to send earthquake location and magnitude since 2013. Romanian territory, together with the neighbor countries Moldova, Ukraine and Bulgaria, are periodically affected by the intermediate depth earthquakes originating from Vrancea area. In order to rapidly locate and estimate magnitude are used a few seconds of strong motion acceleration data. The alert notification broadcasting to users uses an internal communication network built on redundant links with a very high availability. When an earthquake is detected at the surface by the 24 bits accelerometers and velocity sensors, the digital seismic data is sent in real time to the National Institute for Earth Physics where the first 4 s of data are analyzed and alert is issued. The alert is sent to the users using TCP/IP or UDP communication protocols. At the emergency response units there are computers and dedicated devices that have three levels of warning according to the magnitude of the earthquake. Warning levels are associated to different management systems of strategic facilities than can block or enable automatically chosen activities of those facilities. The REWS is sending alerts also to civil protection and Koslodui power plant, in the northern part of Bulgaria. Since the REWS is able to rapidly locate events and compute magnitude, there were no false alerts recorded and were issued 19 earthquake alerts for earthquakes with M > 4.0.

Bridging the Gap Between Nonlinear Seismology as Reality and Earthquake Engineering

In seismic hazard evaluation and risk mitigation, there are many random and epistemic uncertainties. On the another hand, the researches in this area as part of knowledge are with rest, that is, the results are with interpretable questions with open answers. The knowledge cannot be exhausted by results. The authors developed in last time the concept of “Nonlinear Seismology – The Seismology of the XXI Century” (Marmureanu et al. Nonlinear seismology-the seismology of XXI century. In: Modern seismology perspectives, vol 105. Springer, New York, pp 49–70, 2005).