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SUMMARY:Imaging the Seismic Velocity Structure beneath Askja Caldera\, Ice
 land with Traveltime Tomography  - Jifei Han
DTSTART:20230210T160000Z
DTEND:20230210T170000Z
UID:TALK196531@talks.cam.ac.uk
CONTACT:David Al-Attar
DESCRIPTION:  Askja caldera is a large central volcano located in the 
 Northern Volcanic Zone in Iceland. It has experienced a number of eruption
 s in modern history with one of the largest taking place in 1875. After it
 s most recent eruption in 1961\, GPS measurements have shown that deflatio
 n has continued since the 1980s\, which may primarily be caused by the coo
 ling of a shallow magma body as suggested by geodetic modeling. In ~Septem
 ber 2021\, the Askja caldera switched from deflation to inflation. This ha
 s caused a lot of excitement in the seismology and volcano communities\, w
 ith increased monitoring and data collection beginning in earnest in an at
 tempt to better evaluate the progress and potential outcomes of this inter
 esting phenomenon.\n      My study aims to image the seismic v
 elocity structure beneath the top ~10 km of the Askja caldera and the surr
 ounding region using traveltime tomography. The dataset consists of the fi
 rst arrival picks of P- and S-waves from local earthquakes. The initial da
 taset is sourced from Greenfield et al. (2016)\, but additional picks from
  more recently collected data are also incorporated to enhance ray coverag
 e. These arrival times are inverted using the FMTOMO package\, which joint
 ly constrains hypocenter location and 3-D Vp\, Vs and Vp/Vs structure usin
 g an iterative non-linear approach\, in which the forward problem of trave
 ltime prediction is solved using the Fast Marching Method (Rawlinson et al
 .\, 2005).\n      The final tomographic results yield a variet
 y of wavespeed anomalies that can be associated with the volcanic plumbing
  system. Of particular note is a low Vp\, low Vs and high Vp/Vs conduit be
 neath the caldera\, which is consistent with the flux of melt through the 
 crust. Outside the conduit\, high-velocity anomalies align with the layout
  of the caldera. This may reflect the presence of solidified intrusive roc
 ks. Southeast of the caldera is dominated by a low Vp\, high Vs anomaly th
 at is likely associated with the geothermal area. Synthetic checkerboard a
 nd spike tests indicate that these features are constrained by the data.\n
  \nReferences:\n--Rawlinson\, N. and Sambridge\, M. (2005). The fast march
 ing method: an effective tool for tomographic imaging and tracking multipl
 e phases in complex layered media. Exploration Geophysics\, 36(4):341.\n--
 Greenfield\, T.\, White\, R. S.\, and Roecker\, S. (2016). The magmatic pl
 umbing system of the Askja central volcano\, Iceland\, as imaged by seismi
 c tomography. Journal of Geophysical Research: Solid Earth\, 121(10):7211
 – 7229.
LOCATION:Tea Room\, Old House
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