Microaftershock survey of the 1978 Bermuda rise earthquake
On March 24, 1978, a magnitude 6.0 intraplate earthquake occurred 380 km southwest of Bermuda near magnetic anomaly M4 (roughly-equal118 m.y.B.P.). A catalog of seismicity for the Bermuda rise indicates that this is an area of significant intraplate seismicity in the western North Atlantic Ocean. The fault plane solution for the 1978 event is of thrust type and strikes 340/sup 0/, in an intermediate direction to the trends of major fracture zones (300/sup 0/) and abyssal hill topography (035/sup 0/) in the area. The P axis of this mechanism is nearly horizontal and trends 259/sup 0/, subparallel to the absolute plate motion vector for North America. Aftershock activity was detected teleseismically for approximately 8 months after March 24, and the entire sequence is best described as a prolonged mainshock-aftershock series. During June 18--28, 1978, we conducted a microaftershock survey of the area using ocean bottom hydrophones and recorded 250 events (0<2). These smaller events are located in a tight cluster 5--10 km northeast of the NEIS mainshock location. SP-P data from microaftershocks recorded during this survey indicate a relatively narrow band of activity (about 10 km wide), smaller than would be inferred based on NEIS aftershock locations alone. Many of the recorded microaftershocks exhibited prominent water wave phases, which have been used to constrain further the epicentral locations. The depths of these events, while not well determined, appear to be shallow, i.e., less than 5 km below the seafloor. The spatial clustering of seismicity near the perimeter of the rise suggests that variations of crustal thickness associated with the Bermuda rise may be responsible for triggering intraplate seismicity in this region.
- Research Organization:
- Lamont-Doherty Geological Observatory and Department of Geological Sciences of Columbia University, Palisades, New York 10964
- OSTI ID:
- 6214510
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 87:B13
- Country of Publication:
- United States
- Language:
- English
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Bermuda earthquake of March 24, 1978: A significant oceanic intraplate event
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