Moho Topography and Velocity/Density Model for the Hedmarken area, Eastern Norway, using Receiver Function Analysis and Rj-McMC

<p>A Receiver Function Analysis was carried out in the Mjøsa area, Eastern Norway, in order to better image this tectonically complex area, understand the crustal contrasts and complement geological analysis that were made previously in the area. For this, we used seismic traces received for seven broadband stations from the NORSAR permanent array. The H-K (depth vs Vp/Vs) stacking procedure and a Reversible jump Markov chain Monte Carlo (Rj-McMC) inversion were developed independently. The first analysis allows us to obtain a model with the Mohorovicic discontinuity values under each seismic station and the average Vp/Vs crustal ratio. With the inversion, it was possible to develop a 1D local velocity model. Applying the Nafe-Drake relationship, a 2D density model was obtained and tested against observed gravity. Results indicate the presence of a low anomalous density layer that is located to the NNW of the study area, which is probably related to low-density meta-sediments in the Åsta Basin located above the basement. A main crustal fault is also indicated from the density model, spatially coinciding with faults grown during the Sveconorwegian orogenic process.</p><p> </p>

HISTORY OF SEISMOLOGY IN CROATIA

The work of Andrija Mohorovičić (1857–1936) had a large impact on the development of seismology, both in Croatia and world-wide. This paper presents a chronological survey of the development of seismology in Croatia providing context for the discovery of the Mohorovičić discontinuity in 1910. The development of early Croatian seismology was strongly influenced by advances in the field made in both Europe and world-wide. It also was influenced by several strong earthquakes that occurred within its territory, most notably the 1880 Zagreb earthquake, and the 1909 Kupa Valley (Pokupsko) earthquake. By studying the seismograms from the Kupa Valley earthquake, Mohorovičić was able to prove the existence of the boundary layer between the Earth's crust and the mantle (the Mohorovičić discontinuity). After Mohorovičić retired in 1921, seismological research in Croatia lost much of it's momentum, and for 20 years no seismological papers were published. After World War II, the Geophysical Institute was incorporated into the Faculty of Science of the University of Zagreb, and seismologists became active once more. Beginning in the second half of the twentieth century, the scientific interests of Croatian seismologists broadened, and international cooperation intensified. During that time, the number of active seismologists in Croatia varied, but never exceeded twelve, all of whom were affiliated with the Department of Geophysics of the Faculty of Science at the University of Zagreb. This small seismological community bore the responsibility of maintaining high standards in seismological research and education, and of keeping Croatian seismology visible in the world of geophysical sciences.

Gravimetric Studies in the Sea of Japan

Marine gravimetric studies were carry out in the waters of the Sea of Japan and the Tatar Strait. Maps of the gravitational field of the earth were completed, structural density modeling was executed, the depth of the Mohorovičić discontinuity was determined.

Probing layered arc crust in the Lesser Antilles using receiver functions

Oceanic arcs can provide insight into the processes of crustal growth and crustal structure. In this work, changes in crustal thickness and composition along the Lesser Antilles Arc (LAA) are analysed at 10 islands using receiver function (RF) inversions that combine seismological data with v P /v S ratios estimated based on crustal lithology. We collected seismic data from various regional networks to ensure station coverage for every major island in the LAA from Saba in the north to Grenada in the south. RFs show the subsurface response of an incoming signal assuming horizontal layering, where phase conversions highlight discontinuities beneath a station. In most regions of the Earth, the Mohorovičić discontinuity (Moho) is seismically stronger than other crustal discontinuities. However, in the LAA we observe an unusually strong along-arc variation in depth of the strongest discontinuity, which is difficult to explain by variations in crustal thickness. Instead, these results suggest that in layered crust, especially where other discontinuities have a stronger seismic contrast than the Moho, H– k stacking results can be easily misinterpreted. To circumvent this problem, an inversion modelling approach is introduced to investigate the crustal structure in more detail by building a one-dimensional velocity–depth profile for each island. Using this method, it is possible to identify any mid-crustal discontinuity in addition to the Moho. Our results show a mid-crustal discontinuity at about 10–25 km depth along the arc, with slightly deeper values in the north (Montserrat to Saba). In general, the depth of the Moho shows the same pattern with values of around 25 km (Grenada) to 35 km in the north. The results suggest differences in magmatic H 2 O content and differentiation history of each island.