Open AccessThrust faulting and crust—upper mantle structure in East Australia
Author(s) -
Mills Joseph M.,
Fitch Thomas J.
Publication year - 1977
Publication title -
geophysical journal of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0016-8009
DOI - 10.1111/j.1365-246x.1977.tb03677.x
Subject(s) - geology , seismology , crust , aftershock , thrust fault , tectonics , compression (physics) , fault (geology) , cenozoic , volcanism , geophysics , geomorphology , structural basin , materials science , composite material
Summary. The mid‐crustal earthquake of 1973 March 9 (m b = 5.5, h ≤ 20 km) located 60 km south‐west of Sydney, Australia, provides unambiguous evidence of contemporary thrust faulting in South‐eastern Australia — a region of high heat flow and Cenozoic basaltic volcanism. Aftershock locations suggest a steeply dipping fault in the depth range from 8 to 24 km with a lateral extent of about 8 km. The mechanism solution is consistent with a tectonic stress field that is dominated by east—west horizontal compression. A seismic moment of 5.7 ± 10 23 ± 20 per cent dyne‐cm was computed from surface‐wave amplitudes. Minimum values of slip and stress drop, 2 cm and 1 bar respectively, were estimated from the moment and a fault size taken’ from aftershock locations. Refinement modelling by a controlled Monte Carlo technique was used to provide unbiased models directly from multimode group velocities. The dispersion of fundamental and higher mode surface waves recorded at the digital high‐gain station at Charters Towers, Queensland, and the WWSSN station at Adelaide, South Australia, is satisfied by crust‐ and upper‐mantle models which have neither pronounced S‐wave low‐velocity zones nor thick high‐velocity lids within 140 km of the Earth's surface. These models have subcrustal shear velocities of 4.20–4.32 km/s which are 0.4–0.5 km/s slower than Canadian shield shear velocities (CANSD).