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Type of faulting and orientation of stress and strain as a function of space and time in Kilauea's south flank, Hawaii

Journal of Geophysical Research B: Solid Earth

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Abstract

Earthquake focal mechanisms of events occurring between 1972 and 1992 in the south flank of Kilauea volcano, Hawaii, are used to infer the state of stress and strain as a function of time and space. We have determined 870 fault plane solutions from P wave first motion polarities for events with magnitudes ML ??? 2.5 and depth ranging between 6 and 12 km. Faulting is characterized by a mixture of decollement, reverse, and normal faults. Most large earthquakes with magnitude M < 7 slip on reverse faults striking NE at 40?? and dipping SE between 60?? and 70??. In Hawaii, the earthquakes with M > 7 rupture the decollement plane, since it is the only surface large enough to generate magnitude 7 or larger earthquakes. The percentage of reverse faulting events is high compared to the decollement and normal faulting mechanisms for the period 1972-1983. The percentage of decollement type focal mechanisms becomes dominant after 1983. This pattern of faulting activity suggests that pressure was building up within Kilauea's rift zone prior to the 1983 Puu'Oo eruption. Overall, a single stress orientation with the maximum compressive stress oriented SE perpendicular to the rift and dipping at 45?? is compatible with the coeval existence of decollement, reverse, and normal faults. However, in a crustal volume east of longitude 155??10'W, we find a change of the orientation of ??1 from nearly horizontal to plunging 45?? SE occurring in 1979. This stress rotation suggests magma movements within the aseismic part of Kilauea's east rift zone. The strain and stress orientations are coaxial in the south flank except within the volume where the stress rotation is observed. We observe a change in the relationship between stress and strain directions caused either by the shifting of seismic activity from reverse faults to decollements, while stress stays constant, or by a rotation of stress, while strain remains constant. Assuming that the model of a noncohesive Coulomb wedge is appropriate for Kilauea's south flank, we find that high pore pressures are prevalent along the decollement and within the wedge for a coefficient of friction equal to 0.85.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Type of faulting and orientation of stress and strain as a function of space and time in Kilauea's south flank, Hawaii
Series title:
Journal of Geophysical Research B: Solid Earth
Volume
101
Issue:
7
Year Published:
1996
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of Geophysical Research B: Solid Earth
First page:
16025
Last page:
16042
Number of Pages:
18