11:00 〜 13:00
[SIT19-P11] Travel time anomalies in Chile Triple Junction region
The Chile Triple Junction (CTJ) is the point where the Antarctic, Nazca, and South American plates meet and is presently a ridge-trench-trench triple junction. As a consequence of the Chile ridge subduction, a slab window, which is a gap within the subducting oceanic lithospheres, is considered to be developed beneath southern Patagonia. We analyzed broadband seismograms to constrain the seismic velocity structure beneath the forearc region in the vicinity of the CTJ.
The seismic array of 13 Ocean Bottom Seismometers (OBS) had been deployed just south of CTJ for approximately two years, from 2019 January to 2021 January (Ito et al. 2022, in this meeting). We also collected broadband seismograms of stations within the distance of 30° of the OBS array via the IRIS (Incorporated Research Institutions for Seismology). We measured absolute P-wave travel times by the Adaptive Stacking method (Rawlinson and Kennett, 2004) and differential travel times of all possible station pairs by cross-correlating two seismograms.
The figure shows measured absolute travel time residuals from iasp91(Kennett and Engdahl, 1991) for an event indicated as a red star in the upper left map. A travel time advance was broadly observed in the northern regions of CTJ, which might be due to low temperature and thus high-velocity Nazca slab. In contrast, on the south side of CTJ, where seismicity and arc volcanism gap are known, traveltime delays were detected. These delays may be associated with the slab window with higher temperatures than the surrounding lithosphere. We plan to perform finite-frequency tomography using these travel time data to estimate the three-dimensional P wave velocity structure for further analysis, which is expected to provide high-resolution tomographic imaging of the deep interior below the CTJ.
The seismic array of 13 Ocean Bottom Seismometers (OBS) had been deployed just south of CTJ for approximately two years, from 2019 January to 2021 January (Ito et al. 2022, in this meeting). We also collected broadband seismograms of stations within the distance of 30° of the OBS array via the IRIS (Incorporated Research Institutions for Seismology). We measured absolute P-wave travel times by the Adaptive Stacking method (Rawlinson and Kennett, 2004) and differential travel times of all possible station pairs by cross-correlating two seismograms.
The figure shows measured absolute travel time residuals from iasp91(Kennett and Engdahl, 1991) for an event indicated as a red star in the upper left map. A travel time advance was broadly observed in the northern regions of CTJ, which might be due to low temperature and thus high-velocity Nazca slab. In contrast, on the south side of CTJ, where seismicity and arc volcanism gap are known, traveltime delays were detected. These delays may be associated with the slab window with higher temperatures than the surrounding lithosphere. We plan to perform finite-frequency tomography using these travel time data to estimate the three-dimensional P wave velocity structure for further analysis, which is expected to provide high-resolution tomographic imaging of the deep interior below the CTJ.