Abstract
The Central Appalachian Anomaly (CAA) is a region of the upper mantle beneath eastern North America that exhibits pronounced anomalies in its seismic velocity, seismic attenuation, and electrical conductivity structure. The CAA clearly expresses itself in low velocity, high attenuation, and high conductivity values; however, the present-day composition and state of the asthenospheric upper mantle in the anomalous region remains imperfectly known. The collection of data from densely spaced, co-located seismic and magnetotelluric arrays during the Mid-Atlantic Geophysical Integrative Collaboration (MAGIC) experiment affords the opportunity to probe the structure and properties of the upper mantle in the CAA region in detail using multiple types of geophysical observations. Here, we present new observations of P and S wave travel times from teleseismic earthquakes measured at MAGIC stations, including a determination of how travel times deviate from the predictions of a standard 1-D reference model. These observations constrain the ratio of the P to S wave travel time perturbations associated with the CAA, which in turn allows us to estimate the ratio of P and S wave velocity anomalies. We combine these observations with previously published estimates of seismic attenuation and electrical conductivity in the upper mantle beneath the MAGIC array, and carry out forward modeling to determine reasonable ranges of temperature, partial melt fraction, water content, and composition for the CAA. Our results suggest that 1%–2% partial melt is required to simultaneously explain the velocity, attenuation, and electrical conductivity observations beneath the MAGIC array.
| Original language | English (US) |
|---|---|
| Article number | e2022GC010690 |
| Journal | Geochemistry, Geophysics, Geosystems |
| Volume | 24 |
| Issue number | 3 |
| DOIs | |
| State | Published - Mar 2023 |
Bibliographical note
Funding Information:The MAGIC geophysical experiment (Long et al., 2020) was supported by the EarthScope and GeoPRISMS programs of the National Science Foundation (NSF) via Grant EAR-1251515 to Yale University, Grant EAR-1251329 to the College of New Jersey, and Grant EAR-1460257 to the Woods Hole Oceanographic Institution. The authors thank the many landowners and field volunteers who made the MAGIC seismic and MT deployments possible. Support from the Incorporated Research Institutions for Seismology (IRIS) PASSCAL program was invaluable to the success of the MAGIC seismic experiment. The facilities of the IRIS Consortium are supported by the National Science Foundation's Seismological Facilities for the Advancement of Geoscience (SAGE) Award under Cooperative Support Agreement EAR-1851048. The authors are grateful to scientific collaborators on the MAGIC experiment and related projects for useful discussions. The authors thank Shun Karato for helpful discussions and suggestions. The authors thank Karin Sigloch and an anonymous reviewer for thoughtful and constructive comments that improved the paper.
Funding Information:
The MAGIC geophysical experiment (Long et al., 2020 ) was supported by the EarthScope and GeoPRISMS programs of the National Science Foundation (NSF) via Grant EAR‐1251515 to Yale University, Grant EAR‐1251329 to the College of New Jersey, and Grant EAR‐1460257 to the Woods Hole Oceanographic Institution. The authors thank the many landowners and field volunteers who made the MAGIC seismic and MT deployments possible. Support from the Incorporated Research Institutions for Seismology (IRIS) PASSCAL program was invaluable to the success of the MAGIC seismic experiment. The facilities of the IRIS Consortium are supported by the National Science Foundation's Seismological Facilities for the Advancement of Geoscience (SAGE) Award under Cooperative Support Agreement EAR‐1851048. The authors are grateful to scientific collaborators on the MAGIC experiment and related projects for useful discussions. The authors thank Shun Karato for helpful discussions and suggestions. The authors thank Karin Sigloch and an anonymous reviewer for thoughtful and constructive comments that improved the paper.
Publisher Copyright:
© 2023. The Authors.
