Seismic tomography and earthquake locations in the Nicaraguan and Costa Rican upper mantle

Publication Type  Journal Article
Year of Publication  2008
Authors  Syracuse, E. M.; Abers, G. A.; Fischer, K.; MacKenzie, L.; Rychert, C.; Protti, M.; Gonzalez, V.; Strauch, W.
Journal Title  Geochemistry Geophysics Geosystems
Volume  9
Pages  -
Journal Date  Jul 30
ISBN Number  1525-2027
Accession Number  ISI:000258147900001
Key Words  subduction; serpentine; melt; seismic velocities; slab; velocity structure beneath; southern central-america; v-p/v-s; subduction-zone; arc lavas; regional-variations; sediment input; wave velocity; least-squares; travel-times
Abstract  

The Central American subduction zone exhibits large variations in geochemistry, downgoing plate roughness and dip, and volcano locations over a short distance along the arc. Results from joint inversions for Vp, Vp/Vs, and hypocenters from the Tomography Under Costa Rica and Nicaragua (TUCAN) experiment give insight into its geometry and structure. In both Costa Rica and Nicaragua, the intermediate-depth seismic zone is a single layer no more than 10 to 20 km thick. Tomographic images show that throughout Nicaragua and Costa Rica the slowest mantle P wave velocities appear below and behind the volcanic front, indicating likely zones of highest temperature extending 80 to 120 km depth. A sheet of high Vp/Vs, thought to be caused by melt, is imaged directly beneath the Nicaraguan volcanoes, whereas a weaker, broader anomaly is imaged beneath the Costa Rican volcanoes, potentially indicating a greater extent of melting beneath Nicaragua. Within the downgoing plate, anomalously low velocities occur at least 20-30 km below Wadati-Benioff zone seismicity, to depths of 140 km beneath Nicaragua and to 60 km depth beneath Costa Rica. They indicate 10-20% serpentinized upper mantle of the downgoing plate beneath Nicaragua, similar to that inferred from refraction seaward of the trench, but continuing to subarc depths. This unusually hydrated lithosphere may introduce more water into the Nicaraguan mantle, initiating increased amount of melting and fluid flux to the arc.

Notes  

333JDTimes Cited:5Cited References Count:71

URL  <Go to ISI>://000258147900001
DOI  Doi 10.1029/2008gc001963