Intraplate earthquakes: Insight from Seismic Tomography and Earthquake Analysis in Norway and India

As a PhD-Candidate, I am conducting research on intraplate seismicity in Norway and India. My PhD study is part of the IPSIN project (Intraplate Seismicity in India and Norway: Distribution, properties and causes). The project is a collaborative research project between Norway and India under the INDNOR program administered and funded by the Norwegian Research Council. The main objective of project is to improve our seismotectonic understanding of intraplate earthquakes in Norway and India. To achieve the project goal, I am performing seismic tomography and seismicity analysis of earthquakes in Nordland, northern Norway. I am also collaborating with Indian scientists to perform similar tasks in intraplate regions in India.

Here are the descriptions of my current research:

a. Seismic tomography in Nordland, Northern Norway

Nordland has the highest seismicity rate in mainland Norway. Earthquakes occur mostly along the coastal area, and offshore, along the passive margin. In this study, I aim to develop a 3-D seismic velocity model for the crust and the upper mantle of Nordland and use it to explain the effect of crustal lateral heterogeneity on intraplate seismicity in the region. In this study, I discuss the influence of crustal structure on seismicity. Analysis of dominant stress directions from the focal mechanism will also be included. Our interpretation will be linked to geodetical observations. Furthermore, I also plan to perform a gravitational stress modeling using the new 3-D velocity model to study the influence of crustal lateral heterogeneity on the regional stress regime.

b. Hypocenter relocation and source parameters of seismicity in Nordland

Accurate hypocenter location is important to reveal the active fault structures, and the space-time pattern of the seismicity. My plan is to improve the earthquake locations accuracy in Nordland using the newly developed 3-D seismic velocity model. Furthermore, the source mechanisms are going to be examined in more detail, possibly using 3-D waveform modeling for relatively larger earthquakes. Later, I will invert the focal mechanism data to obtain the principal stress components.

I will use the relocated hypocenters, focal mechanism solutions, and principal stress components to investigate the faulting geometry, seismogenic depth, and the seismicity relation to the regional stress. Furthermore, I plan to investigate several clusters of earthquakes along the coastal area, e.g., the crust around Rana where most notable events occurred, e.g., the M 5.9 1819 earthquake, the 1979 seismic swarms and the recent 2015 swarms. In the 2015 swarm cluster, the earthquakes occurred from a very shallow depth (< 2 km) to more than 10 km.

Figure: Raypath (gray lines) distribution for seismic tomography in Northern Norway.

Photo:

Hasbi Ash Shiddiqi, UiB

Selected publications:

H. A. Shiddiqi, P. P. Tun, T. L. Kyaw, L. Ottemöller (2018),  Source Study of the 24 August 2016 Mw 6.8 Chauk, Myanmar, Earthquake,  Seismological Research Letters, https://doi.org/10.1785/0220170278.

• H. A. Shiddiqi, P. P. Tun, L. Ottemöller (2019), Minimum 1D Velocity Model and Local Magnitude Scale for Myanmar, Seismological Research Letters. https://doi.org/10.1785/0220190065.

• K. Newrkla, H. A. Shiddiqi, A. E. Jerkins, H. Keers, L. Ottemöller (2019), Implications of 3-D Seismic Raytracing on Focal Mechanism Determination, Bulletin of the Seismological Society of America, https://doi.org/10.1785/0120190184.

• A. E. Jerkins, H. A. Shiddiqi, T. Kværna, S. J. Gibbons, J. Schweitzer, L. Ottemöller, H. Bungum (2020), The 30 June 2017 North Sea Earthquake: Location, Characteristics, and Context, Bulletin of the Seismological Society of America, https://doi.org/10.1785/0120190181.