b'Geophysics in the surveysNewsthe edges of wide bodies. Over narrowTMI_Tzz: Combination of Txx and Tyyamplitude. This removes amplitude bodies, the peaks occur over the centres,provide a measurement in the downwardcharacteristics from the grid file and therefore, the AS in principal providescomponent (Tzz - vertical gradient). results in a grid that equalises the high indications of the magnetic sourceand low amplitudes.geometry. TMI_VRTP: The RTP Reduction to the pole filter attempts to transform theTMI_VRTP_TILT: The tilt filter calculates TMI_BigT: BigT = sqrt( Tx* Tx + Ty*input field data by converting thethe arctan of the angle between the Ty + Tz* Tz) frequency components to that whichvertical gradient and the horizontal would be observed at the Earths pole.gradient of the magnetic field (VRTP).In case of induced magnetisation only,Anomalies at low magnetic latitudes the curvature of RTP and BigT should bewhich are generally asymmetric inTILT = arctan( dM/dz / sqrt( dM/dx in sync, if not there is the likelihood ofappearance will be converted to^2 + dM/dy ^2) )remanence. So if the RTP tilt (curvature) issymmetric anomalies directly over theWhere M = the magnetic anomaly.negative and the BigT tilt is positive theresource body. The VRTP filter consists is remanence. This works quite well onof the standard RTP filter, where theAll images are available for free sharp (near surface) anomalies but fails indataset is divided into a number of tiles.download via SARIG (https://map.basin areas. The origin longitude and latitude varysarig.sa.gov.au/). For assistance with TMI_BigE: BigE = sqrt(( ( Txx+ Txy+ Txz)*for the centre of each tile. This processdownloads please contact Customer ( Txx+ Txy+ Txz) + ( Txy+ Tyy+ Tyz)*( Txy+endeavours to increase the RTP resultServices (dem.customerservices@Tyy+ Tyz) + ( Txz+ Tyz+ Txz)*( Tzz+ Txy+over large areas. sa.gov.au).Txz) )/2)TMI_VRTP_AGC: The Automatic GainGary Reed, Tim Keeping, George Gouthas, TMI_TZ: TZ is the vertical component ofcontrol filter (AGC) converts magneticPhilip Heath the total magnetic field (TMI) derived bywaveforms of variable amplitudeGeological Survey of South Australia a phase transform. into waveforms of close to constantPhilip.Heath@sa.gov.auUpdate on the AusArray SA and Lake Eyre Basin passive seismic arraysOver the course of several trips from mid-August to mid-October, the GSSA carried out the second service run of the AusArray SA broadband passive seismic array. With our ANU collaborators unable to enter South Australia due to COVID restrictions, the GSSA also took on the mantle of servicing the Lake Eyre Basin seismic array (Figures 1 and 2). Having racked up a cumulative 14 500 km in our trusty LandCruiser, we are pleased to have another tranche of seismic data to analyse and fresh batteries and memory cards in the seismic stations to see them through the coming summer.The composite AusArray SA and Lake Eyre Basin array will shed light on the 3D seismic structure of the eastern Gawler Craton and its margins. Data from the permanent stations of the Australian National Seismic Network and Australian Seismometers in Schools program, and from preceding temporary arrays, will also be leveraged (Figure 1).A range of passive seismic modelling techniques will be applied to map the structure of the eastern Gawler Craton from the upper crust to the lithosphere-asthenosphere boundary (e.g., body and surface waveFigure 1.Passive seismic stations in South Australia, past and present.DECEMBER 2021 PREVIEW 22'