Lateral Variations In Seismic Velocities Research Articles

Lateral Variations in Seismic Velocities in the Central Australian Region from Both Conventional and Experimental Seismic Reflection Profiling

In 1985, the Australian Bureau of Mineral Resources recorded 500 km of deep seismic reflection data across the Arunta Block and the Ngalia and Amadeus Basins in central Australia. Large offset shots and expanding reflection spreads were also recorded coincident with the near-vertical incidence reflection data in the Arunta Block and the northern part of the Amadeus Basin to better define seismic velocity variations throughout the crust. In the northern part of the Amadeus Basin lateral and vertical variations in seismic velocity or variable dip in the reflectors can be detected throughout the 10 km thick sedimentary sequence, thus providing useful constraints on lithological or facies variations. A new method of mapping lateral velocity variations below weathering has been developed for interpreting first break data from conventional reflection shots, and has enabled the presence of a northerly-dipping fault in crystalline rocks to be detected in a part of the Arunta Block with few outcrops. The detailed velocity variations measured in selected localities is assisting with the proper migration and interpretation of both shallow and deep reflections.

The New Zealand seismograph network

The New Zealand seismograph network is one of the oldest established and most extensive in the world. From the installation of a Milne seismograph in 1900, it has now grown to consist of 36 permanent stations and two telemetered arrays. The network's stations provide for the recording of world earthquakes over an area that extends from the Pacific Islands to Antarctica, but its main emphasis is given to the study of local seismicity in New Zealand. Instrumentation varies from very low magnification instruments capable of recording the strongest earthquakes, to modern high-magnification networks, and a digitally recording Seismic Research Observatory. A set of portable recorders is also available for field studies. Present analysis procedures are being revised to take account of lateral variations in seismic velocity and attenuation.