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- Keiding, M, et al.
(author)
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Earthquakes, stress, and strain along an obliquely divergent plate boundary : Reykjanes Peninsula, southwest Iceland
- 2009
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In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202 .- 2169-9313 .- 2169-9356. ; 114, s. B09306-
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Journal article (peer-reviewed)abstract
- We investigate the seismicity and the state of stress along the obliquely divergent Reykjanes Peninsula plate boundary and compare the directions of stress from inversion of earthquake focal mechanisms with the directions of strain rate from GPS data. The seismicity on the peninsula since early instrumental recordings in 1926 shows a systematic change from primarily earthquake swarms in the west to main shock-aftershock sequences in the east. The largest earthquakes on the Reykjanes Peninsula typically occur by right-lateral slip on N-S faults and reach magnitude 6 on the eastern part of the peninsula. During 1997-2006 most earthquakes on the Reykjanes Peninsula were located in two areas, Fagradalsfjall and Krisuvik on the central part of the peninsula, as recorded by the South Iceland Lowland (SIL) seismic network. The state of stress estimated by inversion of microearthquake focal mechanisms from the SIL catalogue is mainly oblique strike slip, with a tendency toward a normal stress state. Mapping the directions of the least compressive horizontal stress (S-hmin) shows an average Shmin direction of N(120 +/- 6)degrees E and a remarkable agreement with the directions of greatest extensional strain rate ((epsilon) over dot(Hmax)) derived from GPS velocities during 2000-2006. The agreement between the directions of stress at depth and strain rate observed at the surface indicate that the earthquakes are primarily driven by plate motion.
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| 2. |
- Keiding, M., et al.
(author)
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Strain accumulation along an oblique plate boundary : the Reykjanes Peninsula, southwest Iceland
- 2008
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In: Geophysical Journal International. - 0956-540X .- 1365-246X. ; 172:2, s. 861-872
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Journal article (peer-reviewed)abstract
- We use annual GPS observations on the Reykjanes Peninsula (RP) from 2000 to 2006 to generate maps of surface velocities and strain rates across the active plate boundary. We find that the surface deformation on the RP is consistent with oblique plate boundary motion on a regional scale, although considerable temporal and spatial strain rate variations are observed within the plate boundary zone. A small, but consistent increase in eastward velocity is observed at several stations on the southern part of the peninsula, compared to the 1993-1998 time period. The 2000-2006 velocities can be modelled by approximating the plate boundary as a series of vertical dislocations with left-lateral motion and opening. For the RP plate boundary we estimate left-lateral motion 18(-3)(+4) mm yr(-1) and opening of 7(-2)(+3) mm yr(-1) below a locking depth of 7(-2)(+1) km. The resulting deep motion of 20(-3)(+4) mm yr(-1) in the direction of N(100(-6)(+8))degrees E agrees well with the predicted relative North America-Eurasia rate. We calculate the areal and shear strain rates using velocities from two periods: 1993-1998 and 2000-2006. The deep motion along the plate boundary results in left-lateral shear strain rates, which are perturbed by shallow deformation due to the 1994-1998 inflation and elevated seismicity in the Hengill-Hromundartindur volcanic system, geothermal fluid extraction at the Svartsengi power plant, and possibly earthquake activity on the central part of the peninsula.
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