Geological structure and kinematics of normal faults in the Otway Basin, Australia, based on quantitative analysis of 3‐D seismic reflection data

Abstract

The Otway Basin in the south of Victoria, Australia underwent three phases of deformation during breakup of the southern Australian margin. We assess the geometry and kinematics of faulting in the basin by analysing a 3-D reflection seismic volume. Eight stratigraphic horizons and 24 SW-dipping normal faults as well as subordinate antithetic faults were interpreted. This resulted in a high-resolution geological 3-D model (ca. 8 km 9 7 km 9 4 km depth) that we present as a supplementary 3-D PDF (Data S1). We identified hard-and soft-linking fault connections over the entire area, such as antithetic faults and relay ramps, respectively. Most major faults were continuously active from Early to Late Cretaceous, with two faults in the northern part of the study area active until at least the Oligocene. Allan maps of faults show tectonic activity continuously waned over this time period. Isopach maps of stratigraphic volumes quantify the amount of syn-sedimentary movement that is characteristic of passive margins, such as the Otway Basin. We show that the faults possess strong corrugations (with amplitudes above the seismic resolution), which we illustrated by novel techniques, such as cylindricity and curvature. We argue that the corrugations are produced by sutures between sub-vertical fault segments and this morphology was maintained during fault growth. Thus, they can be used to indicate the kinematics vector of the fault movement. This evidences, together with left-stepping relay ramps, that 40% of the faults had a small component (up to 25°) of dextral oblique slip as well as normal (dip-slip) movement.

3-D seismic exploration across the deep geothermal research platform Groß Schönebeck north of Berlin/Germany

“…In the future, the large offsets of this new data set may also facilitate the application of seismic modeling, for instance using amplitude versus offset (AVO) analyses, to discuss petrophysical reservoir properties. In addition, pre-stack depth migration shall provide the best basis for subsequent geological interpretation and kinematic modeling approaches (c.f., Ziesch et al 2017). Updates of our work will finally encompass results from processing scheme applications, like impedance inversion and seismic attribute mapping (see website: RissDom-A 3D seismics 2018).…”

Near‐surface fault detection using high‐resolution shear wave reflection seismics at the CO2CRC Otway Project site, Australia

“…The interpretation of the regional 3-D data set indicates the termination of this deeply reaching normal fault at ∼400 m below sea level, close to the top Narrawaturk Formation (Figures 2 and 11 [Ziesch et al, 2015]). Extrapolation of the fault from this point to the surface with the same fault dip predicts an intersection with the surface approximately in the southern third of profile PROTECT 1 (Figures 2 and 11, top).…”

“…The shear wave measurements were conducted at locations where known fault zones in a 3-D seismic volume at larger depth (> 400 m) [Ziesch et al, 2015] would intersect the surface, if the faults dipped at the same angle as they do at depth. An illustration of fault zones in the vicinity of the site is given in Figures 2 and 3.…”

“…Therefore, near-surface resolution is limited and the uppermost horizon that can be identified in these sections is the Top Narrawaturk. The paths of shear wave profiles PROTECT 1 and 2 were chosen to cross Fault 2 and Buttress NW [Ziesch et al, 2015], as perpendicular as possible to their strikes. PROTECT 3 was carried out to image the subsurface in the direct vicinity of the CO2CRC wells ( Figure 1).…”

“…Along profiles PROTECT 1 and 2, the newly acquired 2-D shear wave images indeed suggest a continuation of the deeply reaching fault zones to the surface (Figures 12 and 14). This is not the case at profile PROTECT 3, where the fault zone Naylor South dies out at ∼800 m bsl in the interpreted 3-D P wave data [Ziesch et al, 2015]. Even though the new shear wave seismic image of the structures above this fault zone also shows indications of near-surface faults, no direct continuation of the deep structures can be made with faults at the surface (Figure 17).…”