Investigation of the upper mantle beneath the Hawaiian Island chain using PP-precursors

The Hawaiian hotspot is of great geological significance, but data collection in the area can be challenging due to the water depth around these islands. By using PP bounce point data, with receivers in mainland United States, we analyze the area with a greater wealth of data than possible using data collected locally. The increased amount of data, in addition to new beamforming and iterative deconvolution techniques, has increased the frequency content in PP precursor data, from around the traditional 0.01 Hz to above 5 Hz, enabling us to image to shallower depths and thinner layers than previously possible. Profiles of stacked PP precursors across the island chain were produced along perpendicular lines. Data were stacked in bins 1˚ along the profiles and 4˚ perpendicular to the profile (parallel to the island chain). An additional profile was produced some 10˚ away from the island chain as a control group. The control group shows pairs of high- and low-velocity horizons in the mantle. These may be the base and top of shear zones. These horizons are strongly disrupted near the Hawaiian Island chain. In the lithosphere, low velocity zones are more abundant to the south of the island chain but are less common on the north side. If these indicate melt, the low velocity zones may be blocked by the Islands, which are sinking into the lithosphere. As this study and other recent work imply the hot spot is more active to the southwest of the island chain than to the north, the island chain itself may be causing the crust to warp downward into the mantle and could act as a dam to melt migrating to the north. Furthermore, we believe that the island’s weight downwarping the lithosphere causes a crack to propagate out past the youngest island, which also acts as a dam that keeps most of the melt to the southwest of the island chain.