Browsing by Subject "Transportable array"
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Item Investigation of the upper mantle beneath the Hawaiian Island chain using PP-precursors(2013-08) Rogers, Kenneth D.; Gurrola, Harold; Nagihara, Seiichi; Karlsson, Haraldur R.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.Item Seismic analysis of the Rocky Mountain Front and Great Plains using transportable array data(2011-05) Castille, Kristopher A.; Gurrola, Harold; Zhou, Hua-wei; Asquith, George B.USArray seismic data along the Rocky Mountain Front and Great Plains was downloaded from the Incorporated Research Institutions for Seismology (IRIS) to map lithosphere boundaries including the Mohorovičić discontinuity (Moho), Hales discontinuity (Hales), and lithosphere-asthenosphere boundary (LAB). Water-level (i.e. prewhitening) deconvolution in the frequency domain was used to filter out the bad stations. The good stations were further improved by cross-correlating and stacking the vertical component of nearby stations (i.e. beamforming) and simultaneously deconvolved to reduce the need for prewhitening and improve the signal-to-noise ratio in the receiver functions. These stacked move-out corrected receiver functions (SMOCRF) were used to interpret depth and Vp/Vs ratios of features in the lithosphere including the Moho, Hales discontinuity, and the LAB, and related these to the geology of the Rocky Mountain Front and Great Plains. The Moho depth across the Rocky Mountain Front and Great Plains correlates well with the previous geological and geophysical work done from the literature with deep signatures along the Rocky Mountain Front, southern granite-rhyolite belt, and Black Hills area, and shallow signature along the southern portion of the Rio Grande Rift. Crustal Vp/Vs ratios are mostly uniform throughout the study area at 1.73 to 1.76, which is average for continental crust. The Hales discontinuity is 80 to 90 km for most of the study area. This correlates well with the original discovery made by A.L. Hales in 1969. Deeper regions on the Hales may be related to orogenic events from the past. It appears that Precambrian features are preserved in the mantle between the Moho and Hales discontinuity. The lithosphere-asthenosphere boundary can be divided into a shallow northern half and deep southern half in the study area. Vp/Vs ratios for each interval do not vary much throughout the entire study area. However, Vp/Vs ratios mapped for the Hales discontinuity show higher values above the Yavapai-Mazatzal transition zone, which is interpreted to be the boundary of this accreted Proterozoic province. Skeptical of the lithosphere-asthenosphere boundary results due to crustal reverberations affecting the quality of data that can occur with P-to-S imaging. Recommend following up with S-to-P receiver functions.