Hazai földrengések forrásparamétereinek átfogó vizsgálata = Detailed investigation of source parameters for Hungarian earthquakes

Jelen kutatási projekt célja a Magyarországon kipattant földrengések forrásparamétereinek meghatározása volt. Lokális földrengések és mélyszeizmikus mérések beérkezési időadatainak felhasználásával új, hazánk területére jellemző egydimenziós sebesség modellt konstruáltunk. Egy korábban kifejlesztett nemlineáris, probabilisztikus hullámforma inverziós módszerrel meghatároztuk számos lokális földrengés fészekmechanizmusát (momentum tenzorát). Ezzel egyidejűleg egy új, iteratív, Lp norma minimalizációs eljárást fejlesztettünk ki, melynek segítségével az időben változó fészekmechanizmust leíró momentum tenzor függvényeket felbonthatjuk egy időben állandó momentum tenzor és egy ún. forrásfüggvény szorzatára. A térhullámok spektrális analízisével meghatároztuk számos lokális földrengés dinamikus forrásparamétereit: a skaláris momentumot, a feszültségcsökkenés mértékét, az elmozdulást elszenvedő felület nagyságát és az átlagos elmozdulást. Felállítottunk egy lineáris összefüggést a lokális és a momentum magnitúdó között, mely nélkülözhetetlen a modern földrengés-veszélyeztetettség számításokhoz. GPS mérések és földrengések magnitúdó és fészekmechanizmus adatait felhasználva a kárpáti régió két szeizmikusan aktív területe esetében összevetettük a geodéziai és szeizmológiai alakváltozási sebességeket. Eredményeink szerint Magyarországon a kéregbeli deformáció legnagyobb részt aszeizmikus módon megy végbe, míg a Mur-Mürz zónában a szeizmikus deformáció jóval nagyobb szerepet játszik. | The present project was aimed at determining the source parameters for earthquakes occurred in Hungary. As a prerequisite, we have constructed a new one-dimensional velocity model for the territory of Hungary using arrival times of local earthquakes and controlled seismic sources. The focal mechanisms (full moment tensors) of several local earthquakes have been estimated by a non-linear, probabilistic waveform inversion method developed during previous research projects. Simultaneously, we have developed an iterative Lp norm minimization technique to retrieve the best moment tensor and source time function from the moment tensor rate functions obtained by waveform inversion. The dynamic source parameters of several local earthquakes have been calculated by the spectral analysis of body waves in order to derive the seismic moment, stress drop, fault area and average fault slip of the investigated events. We have also established a linear relationship between local magnitude and moment magnitude that is essential in modern seismic hazard calculations. Using GPS and earthquake magnitude and focal mechanism data, we compared the geodetic and seismic strain rates for two seismogenic zones in the Pannonian basin. The low value of the seismic/geodetic strain rate ratio in Hungary is due to the aseismic release of the prevailing compressive stress. In the Mur-Mürz zone, the seismic part of the deformation is notably larger than in the case of Hungary

Characterization and Liquefaction Hazard Assessment of Two Hungarian Liquefied Sites from the 1956 Dunaharaszti Earthquake

The seismicity of Hungary can be considered moderately active, nevertheless contemporary reports from the past approx. 350 years documented surface manifestations of liquefaction occurrences. The last such earthquake was the 1956 Dunaharaszti ground motion, for which the location of two liquefied sites could be identified approx. 60 years after the event. This provided an excellent opportunity to analyze possibly the only accessible liquefied sites in Hungary. Analysis of the two sites included field and laboratory tests allowing the back-calculation of maximum horizontal ground acceleration of the earthquake. This parameter was previously unknown because the closest seismometer saturated during the event. The performed back-analysis using the principles of paleoliquefaction studies was the first of such analyses in the country. In areas with low to moderate seismicity, geotechnical engineers often neglect and overlook liquefaction hazard, however, when it is addressed, the hazard is often overestimated due to improper characterization of the seismic loading and site characterization. To explore this observation more deeply, probabilistic seismic and liquefaction hazard assessment were carried out at the two liquefied sites and it was found that this conclusion is also valid for Hungary, but the degree of conservatism of the pseudo-probabilistic procedures decreases with increasing earthquake return period (lower annual probability of occurrence)

Swiss AlpArray temporary broad-band seismic stations deployment and noise characterization

Abstract. AlpArray is a large collaborative seismological project in Europe that includes more than 50 research institutes and seismological observatories. At the heart of the project is the collection of top-quality seismological data from a dense network of broadband temporary seismic stations, in compliment to the existing permanent networks, that ensures a homogeneous station coverage of the greater Alpine region. This Alp Array Seismic Network (AASN) began operation in January 2016 and will have a duration of at least 2 years. In this work we report the Swiss contribution to the AASN, we concentrate on the site selection process, our methods for stations installation, data quality and data management. We deployed 27 temporary broadband stations equipped with STS-2 and Trillium Compact 120 s sensors. The deployment and maintenance of the temporary stations across 5 countries is managed by ETH Zurich and it is the result of a fruitful collaboration between five institutes in Europe.Published15–291IT. Reti di monitoraggioJCR Journa