Reprocessing of Legacy Seismic Reflection Profile Data and Its Implications for Plate Flexure in the Vicinity of the Hawaiian Islands

Abstract

During 1975‐1988, an academic research ship, R/V Robert D. Conrad, acquired more than 150,000‐line‐km of multichannel seismic reflection profile data from each of the world’s main ocean basins and their margins. This extensive legacy seismic data set, which involved both single ship and two‐ship data acquisition, has been widely used by the marine geoscience community. We report on our experience in reprocessing seismic reflection profile data acquired during Conrad cruise RC2308 to the Hawaiian Islands region in August/September 1982. We show that the application of modern, industry standard processing techniques, including filtering, de‐bubble, deconvolution and migration, can significantly enhance 40+ year old legacy seismic reflection profile data. The reprocessed data reveals more precisely, and with much less scatter, the flexure of Cretaceous Pacific oceanic crust caused by the Pliocene‐Recent volcanic loads that comprise the Hawaiian Islands. A comparison of observed picks of top oceanic crust which has been corrected for the Hawaiian swell and the Molokai Fracture Zone with the calculations of a simple 3‐dimensional elastic plate (flexure) model reveals a best fit elastic plate thickness of the lithosphere, Te, of 26.7 km, an average infill density of 2701 kg m‐3, and a Root Mean Square (RMS) difference between observations and calculations of 305 m. Tests show these results depend weakly on the load density assumed and that the average infill density is close to what would be predicted from an arithmetic average of the flanking moat infill density and the infill density that immediately underlies the volcanic edifice.

A Seismic Tomography, Gravity, and Flexure Study of the Crust and Upper Mantle Structure Across the Hawaiian Ridge: 2. Ka'ena

“…The T e results here are in general accord with the results of Cilli et al (2023) using reprocessed R/V Robert D. Conrad and the R/V Kana Keoki multichannel seismic reflection profile data. They used a similar range of load densities and derived a T e in the range 25.7-27.7 km, slightly higher than the values derived here.…”

“…Despite the large difference in load size and flexure between the two locations, the calculated T e values are similar (25.6 for Ka'ena vs. 26.7 westward of the island of Hawaii). These results are supported by Cilli et al (2023), who used reprocessed legacy MCS data as a basis for additional flexural modeling near O'ahu (T e of 26.7), but largely eastward of the Ka'ena seismic line. Together, these studies confirm that volcanic loads to the west of Hawai'i are largely compensated by flexure.…”

“…However, the recent seismic, gravity, and plate flexure studies conducted along the Hawaiian-Emperor Seamount Chain (including this study, MacGregor et al, 2023, Watts et al, 2021Xu et al, 2022) collectively provide clear evidence for shallow magmatic emplacement and contradict the notion of significant magmatic underplating for ages at the time of loading of ∼57 Ma (Emperor Seamounts) and ∼90 Ma (Hawaiian Ridge). Additionally, reprocessing of the legacy data of Watts et al (1985) did not find evidence for underplating (Cilli et al, 2023;Lindwall, 1988). These findings invalidate a simple age-related hypothesis.…”

“…(1985), the differences in interpretation (no underplating vs. underplating) may simply indicate that underplating is variable along the ridge. However, reprocessing of the earlier seismic data has not found evidence for underplating (Cilli et al., 2023; Lindwall, 1988) and other recent studies of the Hawaiian‐Emperor Seamount Chain have also not found evidence for underplating (McGregor et al., 2023; Watts et al., 2021; Xu et al., 2022).…”

A Seismic Tomography, Gravity, and Flexure Study of the Crust and Upper Mantle Structure of the Hawaiian Ridge: 1

“…The flexure was modeled assuming different values of the average load, average infill and mantle densities and flexural rigidity and equivalent elastic thickness, T e . Initially, the same set of parameters was used for all three loads as had been derived by optimal minimization (Cilli et al., 2023) from reprocessed R/V Robert D. Conrad MCS data acquired in the vicinity of O'ahu (i.e., average load density = 2,737 kg/m 3 , average infill density = 2,701 kg/m 3 , mantle density = 3,300 kg/m 3 and T e = 26.7 km). The resulting RMS difference between observed and calculated possible top of oceanic crust and the upper and lower seismic reflector positions (Figure 7) were 1.1, 0.9, and 0.7 km respectively (Model 1, Table 2).…”