Modeling the seismic signature of structural data from the Oman Ophiolite: Can a mantle diapir be detected beneath the East Pacific Rise?

[1] We present modeling of the seismic delay time signature of mantle diapirs mapped in the Oman ophiolite and compare these results with those of active source seismic experiments conducted along the East Pacific Rise. To do so, we construct models of shallow-mantle, seismic anisotropy that are consistent with Oman diapirs of different size. Forward calculations of the delay time anomalies due to a combination of diapirrelated seismic anisotropy and isotropic velocity structure are compared with those of a two-dimensional anisotropy field within the same isotropic velocity structure. In the presence of an isotropic, low-velocity anomaly comparable to that imaged beneath the East Pacific Rise, there are only minor differences between the predicted signals of twoand three-dimensional (diapiric) flow. Tomographic modeling is used to determine if the synthetic data for a diapiric model (with a low-velocity isotropic anomaly) can be fit by twodimensional anisotropy and three-dimensional velocity variations. The recovered isotropic anomalies are in good agreement with the synthetic model. However, if the diapir is large enough, artifacts are generated near the corners of the model and, locally, at the ridge axis, with slightly higher velocities. Our results indicate that tomographic analyses of existing travel time data from the East Pacific Rise cannot be used to rule out the presence of diapirs beneath an active spreading center if they are similar in scale to those mapped in Oman.