Constraints on the Geometry of the Subducted Gorda Plate From Converted Phases Generated by Local Earthquakes
The largest slip in great megathrust earthquakes often occurs in the 10–30 km depth range, yet seismic imaging of the material properties in this region has proven difficult. We utilize a dense onshore-offshore passive seismic dataset from the southernmost Cascadia subduction zone where seismicity i...
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| Other Authors: | |
| Format: | Article |
| Language: | English |
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American Geophysical Union (AGU)
2022
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| Online Access: | https://hdl.handle.net/1721.1/140379 |
| _version_ | 1826212254001922048 |
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| author | Gong, Jianhua McGuire, Jeffrey J. |
| author2 | Woods Hole Oceanographic Institution |
| author_facet | Woods Hole Oceanographic Institution Gong, Jianhua McGuire, Jeffrey J. |
| author_sort | Gong, Jianhua |
| collection | MIT |
| description | The largest slip in great megathrust earthquakes often occurs in the 10–30 km depth range, yet seismic imaging of the material properties in this region has proven difficult. We utilize a dense onshore-offshore passive seismic dataset from the southernmost Cascadia subduction zone where seismicity in the mantle of the subducted Gorda Plate produces S-to-P and P-to-S conversions generated within a few km of the plate interface. These conversions typically occur in the 10–20 km depth range at either the top or bottom of a ∼5 km thick layer with a high Vp/Vs that we infer to be primarily the subducted crust. We use their arrival times and amplitudes to infer the location of the top and bottom of the subducted crust as well as the velocity contrasts across these discontinuities. Comparing with both the Slab1.0 and the updated Slab2 interface models, the Slab2 model is generally consistent with the converted phases, while the Slab1.0 model is 1–2 km deeper in the 2–20 km depth range and ∼6–8 km too deep in the 10–20 km depth range between 40.25°N and 40.4°N. Comparing the amplitudes of the converted phases to synthetics for simplified velocity structures, the amplitude of the converted phases requires models containing a ∼5 km thick zone with at least a ∼10%–20% reduction in S wave velocity. Thus, the plate boundary is likely contained within or at the top of this low velocity zone, which potentially indicates a significant porosity and fluid content within the seismogenic zone. |
| first_indexed | 2024-09-23T15:18:46Z |
| format | Article |
| id | mit-1721.1/140379 |
| institution | Massachusetts Institute of Technology |
| language | English |
| last_indexed | 2024-09-23T15:18:46Z |
| publishDate | 2022 |
| publisher | American Geophysical Union (AGU) |
| record_format | dspace |
| spelling | mit-1721.1/1403792024-06-06T19:36:57Z Constraints on the Geometry of the Subducted Gorda Plate From Converted Phases Generated by Local Earthquakes Gong, Jianhua McGuire, Jeffrey J. Woods Hole Oceanographic Institution The largest slip in great megathrust earthquakes often occurs in the 10–30 km depth range, yet seismic imaging of the material properties in this region has proven difficult. We utilize a dense onshore-offshore passive seismic dataset from the southernmost Cascadia subduction zone where seismicity in the mantle of the subducted Gorda Plate produces S-to-P and P-to-S conversions generated within a few km of the plate interface. These conversions typically occur in the 10–20 km depth range at either the top or bottom of a ∼5 km thick layer with a high Vp/Vs that we infer to be primarily the subducted crust. We use their arrival times and amplitudes to infer the location of the top and bottom of the subducted crust as well as the velocity contrasts across these discontinuities. Comparing with both the Slab1.0 and the updated Slab2 interface models, the Slab2 model is generally consistent with the converted phases, while the Slab1.0 model is 1–2 km deeper in the 2–20 km depth range and ∼6–8 km too deep in the 10–20 km depth range between 40.25°N and 40.4°N. Comparing the amplitudes of the converted phases to synthetics for simplified velocity structures, the amplitude of the converted phases requires models containing a ∼5 km thick zone with at least a ∼10%–20% reduction in S wave velocity. Thus, the plate boundary is likely contained within or at the top of this low velocity zone, which potentially indicates a significant porosity and fluid content within the seismogenic zone. 2022-02-15T19:16:12Z 2022-02-15T19:16:12Z 2021-01-25 Article http://purl.org/eprint/type/JournalArticle 2169-9313 2169-9356 https://hdl.handle.net/1721.1/140379 Gong, J., & McGuire, J. J. (2021). Constraints on the geometry of the subducted Gorda plate from converted phases generated by local earthquakes. Journal of Geophysical Research: Solid Earth, 126, e2020JB019962. en http://dx.doi.org/10.1029/2020jb019962 Journal of Geophysical Research: Solid Earth Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf American Geophysical Union (AGU) Wiley |
| spellingShingle | Gong, Jianhua McGuire, Jeffrey J. Constraints on the Geometry of the Subducted Gorda Plate From Converted Phases Generated by Local Earthquakes |
| title | Constraints on the Geometry of the Subducted Gorda Plate From Converted Phases Generated by Local Earthquakes |
| title_full | Constraints on the Geometry of the Subducted Gorda Plate From Converted Phases Generated by Local Earthquakes |
| title_fullStr | Constraints on the Geometry of the Subducted Gorda Plate From Converted Phases Generated by Local Earthquakes |
| title_full_unstemmed | Constraints on the Geometry of the Subducted Gorda Plate From Converted Phases Generated by Local Earthquakes |
| title_short | Constraints on the Geometry of the Subducted Gorda Plate From Converted Phases Generated by Local Earthquakes |
| title_sort | constraints on the geometry of the subducted gorda plate from converted phases generated by local earthquakes |
| url | https://hdl.handle.net/1721.1/140379 |
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