[S01-P] Poster

[S01-P-06] Stress drop characteristics of the 2008-2016 Storfjorden earthquake sequence

^○Lars Ottemoller¹, Norunn Tjaaland¹, Hasbi Ash Shiddiqi¹, Won-Young Kim² (1.University of Bergen, Norway, 2.Lamont Doherty Earth Observatory, Columbia University, US)

An earthquake sequence started in 2008 with a ML=6.0 earthquake in the Storfjorden area to the southeast of Spitsbergen that is part of the Svalbard archipelago. Since then, more than 2000 earthquakes have been detected by the regional seismic stations with about 30 of them being of moderate size. Most recently (2016) a double earthquake of magnitude ML=5.2 and ML=4.8, respectively, occurred to the northeast of the initial main cluster. While in this intraplate region the dominant compressive stresses were thought to originate from the Northern Mid-Atlantic ridge, the mechanisms found for the larger earthquakes range between strike-slip and normal solutions and indicate pull-apart tectonics due to north-south extension. While this presentation will give an updated overview of the complete sequence, the focus is on estimating static stress drop. For the larger earthquakes stress drop was measured from the source displacement spectra. However, for earthquakes below ML=4.0 we systematically searched for correlated events pairs that were about one magnitude apart. The smaller of the two events was then used as empirical Green's function and deconvolved from the larger event to obtain the source time function. This allowed to look for differences in stress drop between various clusters of correlated events. One of the significant findings was that the largest and initial earthquake had the highest stress drop comparable to other intraplate earthquakes. This result was verified by comparing the observed ground motion data to intraplate attenuation curves.