Legacy product - no abstract available

Ingest Method for UNIX Operators of Data from ACRES CCRS (BIL) Tapes. ACRES Technical Document, Version: 2, October 1997

We investigate two intraplate earthquakes in a stable continental region of southwest Western Australia. Both small-magnitude events occur in the top »1 km of crust and their epicenters are located with an accuracy of »100 m (1¾) using satellite Interferometric Synthetic Aperture Radar (InSAR). For the Mw 4.7 Katanning earthquake (10 October 2007) the average slip magnitude is 42 cm, over a rupture area of »1 km2. This implies a high stress drop of 14-27 MPa and, even for this very shallow earthquake, has important implications for regional seismic hazard assessment. The earthquake rupture extends from a depth of around 640 m to the surface, making it a rarely observed intraplate, surface-rupturing event. Using InSAR observations we estimate the coseismic slip distribution of the shallow earthquake, such estimates being rarely available for small magnitude events. For the Mw 4.4 composite Kalannie earthquake sequence (21-22 September 2005) we use a long-term time series analysis technique to improve the measurement of the co-seismic signal, which is a maximum of 27 mm in the line-of-sight direction. Double difference seismic analysis shows some relocated cluster seismicity which corresponds in timing, location and source parameters to the InSAR-observed deformation. This earthquake is the smallest magnitude seismic event investigated using InSAR and demonstrates the capability of the technique to provide important constraints on small-magnitude coseismic events. The shallow depth of both these events adds weight to the suggestion that earthquakes associated with tectonic processes in this area of Western Australia often initiate in the upper 1 km of crust.

The Australian Geological Survey Organisation (AGSO) carried out a regional water column geochemical 'sniffer' program on the NW Australian Margin, from Dampier to the west of Darwin, over the period 21 September to 23 October 1998.. The overall objective of the survey was to acquire bottom water hydrocarbon data of the Northern Carnarvon Basin, offshore Canning Basin, Yampi Shelf and the Southern Bonaparte Basin, particularly in regard to detecting natural hydrocarbon seepage. A total of 4788 line km of sniffer data were acquired during the program, using the contract vessel TSMV Pacific Conquest. 160 survey lines were completed.Weak to moderate concentrations of methane and moderate to strong concentrations of ethane were detected in the waters surrounding the Wandoo B Platform, Northern Carnarvon Basin. Elsewhere in the northern Carnarvon, Skua, AC/P20, AC/P25-26, AC/P27 and AC/P23 survey areas, detected hydrocarbon seepage was close to background concentration indicating that seepage was either absent or of very low level.Moderate to strong methane and ethane concentrations were detected on parts of the Yampi Shelf. It is significant to note that there is a measure of repeatability of methane and ethane sampled between S176, recorded in 1996 and these data recorded in 1998. The levels measured, coincident with AGSO seismic lines S165, confirm hydrocarbon leakage where the regional seal thins onto the Kimberley Block basement (O'Brien et al., 1998a).

The Australian Geological Survey Organisation (AGSO) carried out a regional water column geochemical `sniffer' program on the north-west Australian continental margin, from 28 July to 02 September 1996. The survey acquired data on bottom water hydrocarbon concentration and composition on the Yampi Shelf, southern Vulcan Sub-basin and Sahul Platform. A primary goal was to detect natural hydrocarbon seepage. A total of 3535 line km (150 survey lines) of sniffer data were acquired during the program, using the RV Rig Seismic. In addition to the sniffer program, the survey tested a new high-resolution seismic cable. Also, a total of eight gravity cores were taken. The principal areas of seepage detected were on the Yampi Shelf where very high, dry, thermogenic gas concentrations (~1%wet) were detected where the regional seal thins onto the Kimberley Block basement (O'Brien et al.,1998a). Principal areas of seepage were located inboard from the Cornea trend. In addition, significantly lower concentrations of relatively wet gas were detected around the Skua field, in the southern Vulcan Sub-basin. Drier, low-level methane seepage was detected around the breached East Swan and Eclipse fields.

The Great Australian Bight airborne laser fluorosensor (ALF) MkII survey was flown in 1989 by BP. The MkII system used a 308nm laser wavelength, longer than the 266nm used in the later MkIII system. The Raman peak wavelength is 344nm and the fluorescence region is 370nm to 580nm. This report is a reinterpretation of the original BP data using ALF_Explorer software. Survey lines were numbered from 1 to 281 but many lines had several segments. A total of 520 line segments were detected in this survey using a line break distance of 100m. Lines 201 and 203 had 92 and 71 segments respectively. A noisy navigation system may have produced apparent breaks on these lines. If the extra segments on these lines are excluded, the survey contains 359 segments. The lines were acquired at approximately 3,000m spacing in a NS orientation and a flying height of 100m. A total of 33,154,869 spectra were processed at an average spacing of 15m to 22m. Each recorded spectrum is the average of ten detected spectra. The averaging was done to reduce the data recording rate, which was limited by the available hardware. The fluorescence response was very weak for the Great Australian Bight ALF survey, requiring a very sensitive detection method. The 3km line spacing is not sufficiently close to detect most fluor clusters. The Great Australian Bight ALF MkII data is probably not suitable for identifying the isolated, low intensity fluors.

The Arafura Sea airborne laser fluorosensor (ALF) MkII survey was flown in 1989 by BP. The survey was designed to detect natural oil seepage over a region of the Arafura Sea, Northern Australia, in an effort to refine the petroleum prospectivity assessment. An area of about 400km by ~150km was surveyed at 5km line spacing. A total of 534,022 fluorosensor spectra were recorded. This report is a re-interpretation of the BP data by Signalworks Pty Ltd using the ALF Explorer? software. A total of 1894 fluors were picked out of the 534,022 recorded spectra in the final interpretation. This is an average fluor density of 3.55 fluors per thousand spectra. The fluorescence response over most of the survey area consisted mainly of relatively low confidence fluors (compared to the more reliable MkIII survey data). While fluor density variations can be seen on the fluor map the geological implications are not clear. Because of its susceptibility to noise, the MkII ALF system produces less confident fluor maps than the MkIII system. Some mapped fluor density variations may be influenced by sea state or water property variations.

The Perth Basin airborne laser fluorosensor (ALF) MkII survey was flown in 1989 by BP. The survey was designed to detect natural oil seepage over a large region of the Perth Basin, Western Australia, in an effort to refine the petroleum prospectivity assessment. An area of about 80km by 400km was surveyed at 5km line spacing. A total of 510,500 fluorosensor spectra were recorded. This report is a re-interpretation of the BP data by Signalworks Pty Ltd using the ALF Explorer software. A total of 1,355 fluors were picked out of the 510,500 recorded spectra in the final interpretation. This is an average fluor density of 2.65 fluors per thousand spectra. The fluorescence response over most of the survey area consisted mainly of relatively low confidence fluors (compared to the more reliable MkIII survey data). High intensity fluors are located in several zones in the middle of the survey, probably over small islands, being caused by the exposed island material fluorescing. While fluor density variations can be seen on the fluor map the geological implications are not clear. Because of its susceptibility to noise, the MkII ALF system produces less confident fluor maps than the MkIII system. Some mapped fluor density variations may be influenced by sea state or water property variations

The AC/P8 airborne laser fluorosensor (ALF) survey is located in the Northern Bonaparte Basin. The survey was flown in three flights between 29th November 1996 and 1st December 1996. Fifty lines were acquired at 500 m spacing in a NW-SE direction. Line lengths ranged from about 26 km to 32 km with a total of 1,490 km acquired. A total of 1,040,856 spectra were collected at an average spacing of 1.34 m to 1.49 m. Of these 249 were selected as confident fluorescence spectra in the second pass interpretation. The majority of fluors were small but there were also a significant number having medium intensity. Fluor clusters were notably absent from the Corallina Field and only a few fluors were located over the Laminaria Field. The relatively high density of fluors ranging up to medium size over the survey may indicate a working source and migration system.

The AC/P16 airborne laser fluorosensor (ALF) survey is located in the Northern Bonaparte Basin, Timor Sea. The survey was flown in one sortie on the 2nd December 1996. Sixteen lines were acquired at 700 m spacing in an E-W direction at a flying height of 100m. Line length ranged from 23 km to 30 km, with a total of 412.9 km acquired. Line 20070 was a repeat of line 10070. A total of 290,337 spectra were collected at a spacing of about 1.42m. Of these, 111 were interpreted as showing confident oil fluorescence spectra. Fluors were mostly of small to medium intensity with none having F/R area ratio larger than 0.75. Most of the fluors were located in the eastern half of the survey in two main clusters. No fluorescence curve trends were noted but the survey area may be too small to show significant trends.