Variations in axial magma lens properties along the East Pacific Rise (9°30′N–10°00′N) from swath 3‐D seismic imaging and 1‐D waveform inversion

Abstract

AbstractWe use three‐dimensional multistreamer seismic reflection data to investigate variations in axial magma lens (AML) physical properties along the East Pacific Rise between 9°30′N and 10°00′N. Using partial‐offset stacks of P‐ and S‐converted waves reflecting off the top of the AML, we image four 2–4 km long melt‐rich sections spaced 5–10 km from each other. One‐dimensional waveform inversion indicates that the AML in a melt‐rich section is best modeled with a low Vp (2.95–3.23 km/s) and Vs (0.3–1.5 km/s), indicating >70% melt fraction. In contrast, the AML in a melt‐poor section requires higher Vp (4.52–4.82 km/s) and Vs (2.0–3.0 km/s), which indicates <40% melt fraction. The thicknesses of the AML are constrained to be 8–32 m and 8–120 m at the melt‐rich and ‐poor sites, respectively. Based on the AML melt‐mush segmentation imaged in the area around the 2005–2006 eruption, we infer that the main source of this eruption was a 5 km long section of the AML between 9°48′N and 51′N. The eruption drained most of the melt in this section of the AML, leaving behind a large fraction of connected crystals. We estimate that during the 2005–2006 eruption, a total magma volume of 9–83 × 106 m3 was extracted from the AML, with a maximum of 71 × 106 m3 left unerupted in the crust as dikes. From this, we conclude that an eruption of similar dimensions to the 2005–2006, one would be needed with a frequency of years to decades in order to sustain the long‐term average seafloor spreading rate at this location.