[Show abstract][Hide abstract] ABSTRACT: Continental convergence between Arabia and Eurasia is taken up by distributed deformation in Iran. At wavelengths large compared with the thickness of the lithosphere this deformation is best described by a continuous velocity field. The only quantitative source of information on the spatial distribution of strain rates within Iran is the record of earthquakes. We find that we can reproduce the style of deformation observed in the seismicity by simply minimizing the rate of work in a continuous viscous medium that has to accommodate the Arabia-Eurasia plate motion between the defined shapes of Iran's rigid borders. When, in addition, we specify central Iran, Azerbaijan, and the southern Caspian basin to be relatively rigid blocks within the deforming zone, then the fit to the style of the observed strain rate distribution is even better. We conclude that much of the pattern of deformation in Iran is predetermined by the shape of its rigid borders and by the disposition of relatively rigid blocks within it. This is likely also to have been a common occurrence in older orogenic belts. We confirm earlier suggestions that earthquakes between 1909 and 1992 can account for only a small part (,- • 10-20%) of the total deformation required by the convergence between the Arabia and Eurasia plates. We then show that the whole plate motion can be accommodated by a velocity field with the same orientations and relative magnitudes of principal strain rates seen in the earthquakes but with larger absolute magnitudes. There is therefore no requirement that the large proportion of aseismic deformation in Iran is substantially different in style, orientation, or distribution from that released seismically in the earthquakes.
Preview · Article · Aug 1995 · Journal of Geophysical Research Atmospheres
[Show abstract][Hide abstract] ABSTRACT: In this study we compare the strain rates obtained from earthquake moment tensors in the time interval 1911-92 in Greece with measured velocities of Satellite Laser Ranging (SLR) stations relative to Eurasia. We find that the SLR measurements do not require strain different in orientation from that seen in the earthquakes, but simply more of it. The clearest deficit is in the SE Aegean where earthquakes this century can account for virtually none of the measured SLR strain rates. By contrast, in the northern Aegean and NW Turkey the earthquakes can account for a substantial part (greater than 50%) of the measured strain rates. By using both geodetic and seismic data to localize apparent deficits in seismically-released strain, this study represents a first step towards using space-based geodesy for crude regional seismic risk assessment.
No preview · Article · Dec 1994 · Geophysical Research Letters
[Show abstract][Hide abstract] ABSTRACT: The 1968 Inangahua, New Zealand, earthquake occurred in the West Coast Basin and Range Province, northwest of the main plate boundary zone in northern South Island. At MS 7.4, it is not the largest known earthquake in the province, but it has been the subject of thorough seismological, geological, and geodetic documentation. Re interpretation of past observations and more recent data, in the light of new structural and tectonic theories, has produced a new source model for the earthquake. The data suggest that at least 4 m of reverse slip occurred on a fault plane dipping 45° to the northwest beneath the northern part of the Grey‐Inangahua Depression, an area previously inferred to be on the footwall of major reverse faults bounding the ranges on either side of the depression. The seismogenic fault may have propagated north and south across older geological structures in recent times. Faulting within basement is occurring on pre‐existing faults and is accommodating some of the compressional component of oblique relative motion across the plate boundary in northern South Island. Discontinuous coseismic fault ruptures are mainly interpreted as secondary features formed in response to widespread shortening within the sedimentary cover (flexural slip folding) imparted by the deeper primary faulting. Ongoing uplift across a late Quaternary fault trace at Manuka Flat possibly represents postseismic slip over the upper part or northern end of the 1968 rupture plane. Although the Inangahua earthquake source mechanism is consistent with the regional late Quaternary tectonic pattern, the regional rate of seismicity is high (perhaps representing clustering) in comparison with average fault slip rates and recurrence intervals in the province.
No preview · Article · Mar 1994 · New Zealand Journal of Geology and Geophysics
[Show abstract][Hide abstract] ABSTRACT: A continuous horizontal velocity field describing the overall deformation of the lithosphere was obtained from the spatial distribution of seismic moment tensors of earthquakes in the Aegean Sea region over the time interval 1909-1983, using the method described by Holt et al. (1991). The velocity field obtained shows a motion of the southern part of the central Aegean toward the SW at about 30 mm/yr, which is in the same direction but at a lower rate than the 50-60 mm/yr predicted from the simple kinematic arguments of McKenzie (1978) and Jackson and McKenzie (1988). The comparison between the calculated and predicted velocities suggests that the majority of the deformation in the upper crust is accommodated by seismic slip on fault.
No preview · Article · Jan 1992 · Journal of Geophysical Research Atmospheres