Source mechanism of the 1987 Vatnafjöll Earthquake in south Iceland

• Published in: Journal of Geophysical Research: Solid Earth
• Main Authors: Bjarnason, Ingi Þorleifur, Einarsson, Páll
• Other Authors: Raunvísindastofnun (HÍ), Science Institute (UI), Verkfræði- og náttúruvísindasvið (HÍ), School of Engineering and Natural Sciences (UI), Háskóli Íslands, University of Iceland
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union (AGU) 1991
• Subjects: Jarðskjálftar; Misgengi (jarðfræði); Jarðskjálftafræði; Suðurland; Vatnafjöll; Iceland
• Online Access: https://hdl.handle.net/20.500.11815/1036; https://doi.org/10.1029/90JB00831

Publisher's version (útgefin grein) The May 25, 1987, Vatnafjöll earthquake occurred on the Mid‐Atlantic plate boundary, at a junction between a transform (the South Iceland Seismic Zone) and a spreading segment (the Eastern Volcanic Zone). The South Iceland Seismic Zone has had the most destructive earthquakes in the history of Iceland with average intervals of 80–100 years and estimated maximum magnitudes around 7. The 1987 Vatnafjöll earthquake was the largest earthquake (mb = 5.8; MS = 5.8; Mw = 5.9) in south Iceland since the 1912 magnitude 7 earthquake and is the first event sufficiently large to allow a meaningful study of source process in this geologically interesting region. Foreshocks and aftershocks of the Vatnafjöll earthquake were located with relatively good accuracy. They define an elongated N‐S epicentral area, 12 km long and 4 km wide with hypocentral depths mostly between 6 and 13 km. We determined centroid source parameters of the Vatnafjöll earthquake by inverting long‐period teleseismic P and SH waves. The centroid source mechanism and foreshock and aftershock distribution indicate N‐S right‐lateral strike‐slip faulting on a near‐vertical plane. The rupture initiated near the base of the crust and propagated upward along an approximately 10‐km‐long fault but did not reach the surface. The centroid depth is well constrained and is between 5 and 8 km depth at the 95% confidence level. The seismic moment is 9.1×1024dyn cm. The source has relatively short duration of 3 s, which may indicate higher stress drop than global average of earthquakes of this size. The South Iceland Seismic Zone is a 70‐km‐long E‐W striking transform zone between two overlapping rift zones, the Eastern and Western Volcanic Zones. It is characterized by “bookshelf” type of tectonics; that is, there is no surface faulting in the direction of the transform. Instead, N‐S right‐lateral strike‐slip faults are distributed along and perpendicular to the transform zone. The Vatnafjöll earthquake has characteristics of ...