Limits of stresses in continental crusts and their relation to the depth‐frequency distribution of shallow earthquakes

Meißner, R.; Strehlau, Jurgen

doi:10.1029/tc001i001p00073

Cited by 451 publications

(205 citation statements)

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“…If it is assumed that a seismic -aseismic boundary is related to the brittle -ductile boundary of the crust (e.g., Sibson, 1982;Meissner and Strehlau, 1982), changes in seismogenic thickness might be expected in the area under study. Constructed rheological profiles indicate that the Central System's southern border acts as a limit between rheological domains.…”

Section: Discussionmentioning

confidence: 99%

Thermal and mechanical structure of the central Iberian Peninsula lithosphere

Tejero

Ruíz

2002

Tectonophysics

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The central Iberian Peninsula (Spain) is made up of three main tectonic units: a mountain range, the Spanish Central System and two Tertiary basins (those of the rivers Duero and Tajo). These units are the result of widespread foreland deformation of the Iberian plate interior in response to Alpine convergence of European and African plates. The present study was designed to investigate thermal structure and rheological stratification in this region of central Spain. Surface heat flow has been described to range from f 80 to f 60 mW m À2 . Highest surface heat flow values correspond to the Central System and northern part of the Tajo Basin. The relationship between elevation and thermal state was used to construct a one-dimensional thermal model. Mantle heat flow drops from 34 mW m À2 (Duero Basin) to 27 mW m À2 (Tajo Basin), and increases with diminishing surface heat flow. Strength predictions made by extrapolating experimental data indicate varying rheological stratification throughout the area. In general, in compression, ductile fields predominate in the middle and lower crusts and lithospheric mantle. Brittle behaviour is restricted to the first f 8 km of the upper crust and to a thin layer at the top of the middle crust. In tension, brittle layers are slightly more extended, while the lower crust and lithospheric mantle remain ductile in the case of a wet peridotite composition. Discontinuities in brittle and ductile layer thickness determine lateral rheological anisotropy. Tectonic units roughly correspond to rheological domains. Brittle layers reach their maximum thickness beneath the Duero Basin and are of least thickness under the Tajo Basin, especially its northern area. Estimated total lithospheric strength shows a range from 2.5Â10 12 to 8Â10 12 N m À1 in compression, and from 1.3Â10 12 to 1.6Â10 12 N m À1 in tension. Highest values were estimated for the Duero Basin. Depth versus frequency of earthquakes correlates well with strength predictions. Earthquake foci concentrate mainly in the upper crust, showing a peak close to maximum strength depth. Most earthquakes occur in the southern margin of the Central System and southeast Tajo Basin. Seismicity is related to major faults, some bounding rheological domains. The Duero Basin is a relative quiescence zone characterised by higher total lithospheric strength than the remaining units. D

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Section: Discussionmentioning

confidence: 99%

Thermal and mechanical structure of the central Iberian Peninsula lithosphere

Tejero

Ruíz

2002

Tectonophysics

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“…For brittle failure or frictional sliding the stress energy increases with depth [Sibson, 1982], and a maximum in seismicity is often observed just above the base of the inferred seismogenic zone [Meissner and Strehlau, 1982 …”

Section: Methodsmentioning

confidence: 99%

Microearthquake characteristics and crustal V_P/V_S structure at the Mid‐Atlantic Ridge, 35°N

Barclay¹,

Toomey²,

Solomon³

2001

J. Geophys. Res.

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Abstract. We report on the results of a microearthquake experiment conducted at the alongaxis bathymetric high of the slow spreading ridge segment near 35øN on the Mid-Atlantic Ridge (MAR). Of a total of 255 microearthquakes recorded during the 43-day experiment, 31 were located near the Oceanographer transform at the northern end of the segment, 79 occurred at the nontransform offset at the southern end of the segment, and 145 were at the segment center. At the segment center, earthquake epicenters lay within the median valley inner floor and formed a -012-kin-long trend paralleling a steep scarp bounding the western wall of the inner valley; focal depths were 3-4 km below the seafloor. Most (80%) of the focal mechanisms for 32 segment center earthquakes are consistent with normal faulting on faults approximately parallel to the axial trend. From a joint inversion for hypocenters and P and S wave velocity structures, we determined a horizontally averaged Vp/V$ ratio that decreases from 2.9 in the shallowmost 300 rn to 1.7 at 2-km depth, and we interpret this decrease as indicating a decreasing contribution of thin cracks to fracture porosity with depth. The maximum depth of seismicity, 4 km, is anomalously shallow compared with other MAR segments at which microearthquake experiments have been carried out. Cross-axis relief is also anomalously low for this segment's center, and on the basis of this and other MAR microearthquake experiments, them appears to be a correlation between cross-axis relief and maximum depth of seismicity. From the correlation of cross-axis relief and inferred crustal thickness we suggest a relationship between thick crust, high crustal temperatures, and low cross-axis relief, in qualitative agreement with thermomechanical models for the depth of the axial valley.

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“…Independently, Meissner and Strehlau [1982] and Chen and Molnar [1983] suggested that reduced seismic activity of the lower crust indicates low ductile flow strength relative to the upper crust. However, mechanical data and flow law parameters on the rheology of rocks typical for the lower crust, i.e., gabbros, metabasites, etc., are still scarce [Caristan, 1982;Shelton and Tullis, 1981;Kirby, 1983;Carter and Tsenn, 1987;Mackwell et al, 1998].…”

Section: Introductionmentioning

confidence: 99%