20 FebEarth Science and Engineering Graduate SeminarTracking Seismic Anisotropy associated with Caldera Collapse
Tracking Seismic Anisotropy associated with Caldera Collapse
  • Dr. Jessica Johnson
  • University of East Anglia
  • Wednesday, February 20, 2019
  • 04:15 PM - 05:15 PM
  • Lecture Hall 1 (2322), Engineering and Science Hall (Building 9)
2019-02-20T16:152019-02-20T17:15Asia/RiyadhTracking Seismic Anisotropy associated with Caldera CollapseLecture Hall 1 (2322), Engineering and Science Hall (Building 9)Karema S. Alaseef

​Abstract: Seismic anisotropy is the variation of seismic wave speed with direction, which is most frequently observed using shear-wave splitting (SWS). Seismic anisotropy in the crust arises when microcracks in subsurface rocks are aligned, for example when the rock is under differential stress. When this occurs, the rock displays a directional variation in seismic velocity, which can be used as a proxy for maximum compressive stress and is also affected by the type of fluid filling the microcracks. Therefore, SWS analysis can be used to detect changes in stress, cracks, and pore-fluid movement during volcanic activity.  In 2018, Kilauea Volcano displayed lava eruptions in its Lower East Rift Zone and collapse events at its summit.  These two regions have not experienced such eruptions since 1960 and 1924, respectively. This activity was accompanied by a magnitude 6.9 earthquake, which is the largest since 1975, and the largest to be associated with eruptive activity historically. The rate at which the summit lava lake and shallow magma reservoir drained caused incremental caldera collapse with very high rates of seismicity and measured deformation. This suggests that large amounts of magmatic fluids were being mobilised, and the rate of change of crustal stresses were high. Even though similar activity has been seen before, it has never been monitored with modern equipment and so this activity provides a completely new data set and presents a unique opportunity to learn about the subsurface processes at Kilauea.  SWS tomography overcomes the problems of heterogeneous anisotropy with migrating seismicity. We are using SWS tomography with the elevated rates of seismicity to image changes in the subsurface over time. In particular, with up to 400 earthquakes a day in the caldera during the collapse, we will be able to watch the crack evolution.  

Bio: Jessica started her career with an undergraduate maters at the University of Leeds (UK). She spent a year at the university of Alberta, Canada, and then returned to Leeds to do her masters project on pong-period earthquakes at Soufriere Hills Volcano in Montserrat. She went on to do a PhD in Volcano Seismology at Victoria University of Wellington in New Zealand. Her project was to discriminate between spatial and temporal variation in seismic anisotropy at volcanoes, mainly focusing on Mount Ruapehu volcano in New Zealand and Mount Okmok volcano in Alaska.   With a fellowship from the USGS and University of Hawaii cooperative agreement, Jessica completed a two year post-doc at the Hawaiian Volcano Observatory, mainly concentrating on finite element modelling of the volcanic system. She then received a Marie Curie fellowship to return to the UK and work at the university of Bristol. She has been a lecturer in Geophysics at the University of East Anglia since 2015 and her most recent project was an urgent response to the 2018 eruption of Kilauea Volcano in Hawaii.


  • Karema S. Alaseef