3D Active Source Seismic Imaging of the Alpine Fault Zone and the Whataroa Glacial Valley in New Zealand

Autor: Vera Lay, Douglas R. Schmitt, Andrew R. Gorman, Malcolm B. Bertram, Stefan Buske, Alexis Constantinou, R. L. Kellett, Jennifer Eccles, Martha K. Savage, John Townend, Randolph Kofman, Kevin W. Hall, Don C. Lawton
Přispěvatelé: Buske, Stefan, 1 Institute of Geophysics and Geoinformatics Technical University Bergakademie Freiberg Freiberg Germany, Townend, John, 3 School of Geography, Environment and Earth Sciences Victoria University of Wellington Wellington New Zealand, Kellett, Richard, 4 GNS Science Lower Hutt New Zealand, Savage, Martha, Schmitt, Douglas R., 5 Purdue University West Lafayette IN USA, Constantinou, Alexis, 6 Schlumberger Riboud Product Centre Clamart France, Eccles, Jennifer D., 7 University of Auckland Auckland New Zealand, Gorman, Andrew R., 8 University of Otago Dunedin New Zealand, Bertram, Malcolm, 9 University of Calgary Calgary AB Canada, Hall, Kevin, Lawton, Don, Kofman, Randolph, 10 Alberta University Edmonton AB Canada
Rok vydání: 2021
Předmět:
Zdroj: Journal of Geophysical Research: Solid Earth
ISSN: 2169-9356
2169-9313
Popis: The Alpine Fault zone in New Zealand marks a major transpressional plate boundary that is late in its typical earthquake cycle. Understanding the subsurface structures is crucial to understand the tectonic processes taking place. A unique seismic survey including 2D lines, a 3D array, and borehole recordings, has been performed in the Whataroa Valley and provides new insights into the Alpine Fault zone down to ∼2 km depth at the location of the Deep Fault Drilling Project (DFDP)‐2 drill site. Seismic images are obtained by focusing prestack depth migration approaches. Despite the challenging conditions for seismic imaging within a sediment filled glacial valley and steeply dipping valley flanks, several structures related to the valley itself as well as the tectonic fault system are imaged. A set of several reflectors dipping 40°–56° to the southeast are identified in a ∼600 m wide zone that is interpreted to be the minimum extent of the damage zone. Different approaches image one distinct reflector dipping at ∼40°, which is interpreted to be the main Alpine Fault reflector located only ∼100 m beneath the maximum drilled depth of the DFDP‐2B borehole. At shallower depths (z
Plain Language Summary: The Alpine Fault in New Zealand is a major plate boundary, where a large earthquake will likely occur in the near future. Thus, it is important to understanding the detailed processes of how and where such an earthquake occurs. Many scientists are involved in this work, particularly in the attempt of drilling through the fault zone with a ∼900 m deep borehole. We analyzed new seismic data from this area using sensors in the borehole and at the surface to record small ground movements caused by a vibrating surface source causing waves that travel through the ground. From these data, we obtained a detailed image of the structures in the subsurface, for the first time in 3D, by applying advanced analysis methods. Hence, we can better understand the shape of the glacial valley and of the fault zone, that is, the local structures of the continental plate boundary. We interpret at least 600 m wide zone of disturbed rocks and identify a potential major fractured plane down to about 1 km depth. Our studies may help to understand structures that host earthquakes in this area.
Key Points: We use focusing prestack depth migration with detailed seismic data to analyze the complex subsurface environment of the Alpine Fault zone. Seismic images show Alpine Fault zone related reflectors at a depth of ∼0.2–1 km dipping ∼40°–56° around the DFDP‐2B borehole. Complex structures within the glacial Whataroa Valley are imaged showing steep valley flanks, faults, and internal sedimentary horizons.
German Research Foundation (DFG)
Earthquake Commission (EQC) http://dx.doi.org/10.13039/100012181
NSERC discovery and Canada Research Chairs Program
Canadian Foundation for Innovation
Databáze: OpenAIRE
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