Hasbi Ash Shiddiqi

Crustal Structure of Nordland: a preliminary result from seismic tomography

Nordland is the most seismically active region in mainland Norway. Historically, the 1819 Lurøy / Rana earthquake (magnitude estimate 5.8 – 6.0) was the largest earthquake in northern Europe for the last 200 years. In recent years, several series of earthquake swarms occurred along the coastal area of Nordland. In this study, we aim to investigate the causative mechanism of intraplate seismicity and swarm in Nordland by using seismic tomography. Additionally, we also intend to investigate the crustal structure variation in this region, especially beneath Lofoten and the Northern Scandinavian mountain. We used 602 earthquakes with a total of ~8000 P- and ~6500 S-wave arrival times recorded by 89 seismic stations. In the inversion, hypocenters, Vp, Vp/Vs and station delays are jointly inverted. Our preliminary Vp model shows a good agreement with the crustal thickness estimate from receiver function studies. We also found a relatively high Vp/Vs ratio in the lower crust below the mainland Nordland. However, more synthetic tests and other quality assessment are needed to confirm the reliability of this anomaly.