GPS Mapping of 1975 Kalapana Earthquake Ground Deformation, Kilauea Volcano, Hawaii

E C Cannon (Department of Geology, One Shields Avenue, University of California at Davis, Davis, CA 95616; 530-752-0350; e-mail:; R Burgmann (Department of Geology and Geophysics, 385 McCone Hall, University of California, Berkeley, CA 94720-4767; (510) 643-9545; e-mail:

Earthquakes in 1868 and 1975 of M > 7 have struck the south flank of Kilauea Volcano, Hawaii. Earth scientists interpret the south flank as a mobile block, bounded to the north by Kilauea Volcano rift zones, and at 10-12 km depth by a shallowly north-dipping decollement surface. Internal to the south flank, normal Hilina and Koae fault systems dissect the south flank block. When the decollement surface ruptured during the November 29, 1975 M=7.2 Kalapana earthquake, south flank surface displacements approached a maximum of 3 m vertical subsidence and 8 m horizontal motion seaward. 1975 Kalapana earthquake surface deformation along the Hilina fault system produced fractures in 1969-1974 Mauna Ulu surface flows. Mapping Kalapana earthquake ground deformation of Mauna Ulu flows will improve our understanding and evaluation of south flank coseismic displacement, kinematic models and seismic hazard assessment.

We employ two systems of GPS equipment to map surface deformation of the 1975 Kalapana earthquake. Field mapping with GPS equipment can record positions of footwall and hangingwall traces of ground deformation, and piercing points across rupture traces. Real-Time Kinematic GPS equipment provides immediate positions with 1 cm horizontal and 2 cm vertical position accuracy. Positions from handheld differential GPS equipment post-processed at the end of each field day provide 2-5 m horizontal and 4-10 m vertical position accuracy. Factors which dictate the type of equipment used include: required level of position accuracy, terrain, vegetation, battery usage. Data processing of field data in map view, and in profile view strike-parallel and strike-perpendicular to fault traces, will be used to calculate ground displacement. These findings will be compared to geodetic measurements collected after the 1975 Kalapana earthquake. Preliminary data analysis shows ground deformation does not concentrate along a single fracture, but rather over a distributed brittle shear zone of 10s to 100s of meters width. En-echelon extensional fractures suggest a strike-slip component of movement on normal Hilina faults.

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