WRA
1. Station Configuration
The station is situated about 35 km to the south-east of the township of
Tennant Creek (approx. population 3500) in the Northern Territory of
Australia, 15 km to the east of the main north-south highway (Stuart
Highway). The location was chosen for its granite outcrops providing near
surface access to hard-rock sites suitable for shallow boreholes.
WRA lies in savannah country with two major seasons. The "dry" extends
from April to October with maximum temperatures in the high 20's and a
prevailing south-easterly wind pattern. The "wet" in the austral summer
from November to March is characterised by higher temperatures and
humidity with periods of considerable rain. Because the area lies on the edge
of the monsoon belt there is considerable variability from year to year, both
in the amount or rain and the duration of the "wet". After rain the normally
dry creeks rise very rapidly and there is considerable inundation of parts of
the array lease making access difficult to the sites at the end of the array
arms. In particularly severe condition the main highways can be cut for
several days.
The array station is about 500 km from the sea in an area with low
population density so that the impact of both microseismic and cultural
noise is low for seismic recording. As a result the station has maintained a
very high standard of data with a very consistent level of event detections
across the year. WRA has contributed to a very large number of the events in
the bulletins of GSETT-3 and the Preliminary IDC. The proximity of the
strong earthquake belt through Indonesia and New Guinea to Fiji-Tonga,
means that there are large numbers of events at distances ranging from 12 to
50 degree. The station also has very good teleseismic detection capabilities.
The configuration of the array lease and its surroundings are illustrated in
Figure 1.1.
Figure 1.1: The Land Holding by the Australian National University (NT Portion 1375)
The Station is situated on NT Portion 1375, an L-shaped parcel of land held
under a Perpetual Crown Lease. Access to the array is from the Stuart
Highway across Aboriginal freehold land (Waramangu Land Trust) such
access is governed by Section 70 (iv) of the Land Rights Act NT 1987 for
property surrounded by Aboriginal land. A formal access Sacred Site Protection
and Access Agreement has been signed with the Central Land
Council in Alice Springs representing the Traditional Owners.
Activities on the site are subject to the stringent provisions of the Northern
Territory Aboriginal Sacred Sites Act 1989 and the Aboriginal Land rights
(Northern Territory) Act 1976, which protect sites of significance to the
Aboriginal Peoples. The upgraded configuration of the seismic array and the
proposed siting of the infrasound array avoid the band of land associated
with the "Flying Fox Dreaming" of the Waramangu people.
Plate 1.1: The central facilities at WRA
The central recording station is an air-conditioned building with 240 V AC
power provided by a twin diesel generator system (with auto-switch over).
Close to the main station building are also good facilities for equipment
maintenance (mechanical and electronic). This whole central complex is now
surrounded by a security fence. The normal complement of staff is two
technical personnel. The remoteness of the site means that the station
needs to be self-sufficient
(replacement parts are rarely obtainable in less than 48 hours) and this
imposes considerable responsibility on the Station staff.
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