Abstract. Many metallic mineral deposits have sufficient physical property contrasts, particularly density,to be detectable using seismic methods. These deposits are sometimes significant for our society andeconomic growth and can help to accelerate the energy transition towards decarbonization. However,their exploration at depth requires high-resolution and sensitive methods. Following a series of2D seismic trials, a sparse, narrow source–receiver azimuth, 3D seismic survey was conducted inthe Blötberget mine, in central Sweden, covering an area of approximately 6 km2 fordeep-targeting iron oxide deposits and their host rock structures. The survey benefited from acollaborative work by putting together 1266 seismic recorders and a 32 t vibrator,generating 1056 shot points in a fixed geometry setup. Shots were fired at every 10 mwhere possible, and receivers were placed at every 10–20 m. Notable quality data were acquireddespite the area being dominated by swampy places as well as by built-up roads and historicaltailings. The data processing had to overcome these challenges for the staticcorrections and strong surface waves in particular. A tailored for hardrock setting and processing workflow wasdeveloped for handling such a dataset, where the use of mixed 2D and 3D refraction staticcorrections was relevant. The resulting seismic volume is rich in terms of reflectivity, with clearsoutheast-dipping reflections originating from the iron oxide deposits extending vertically andlaterally at least 300 m beyond what was known from available boreholes. As a result, weestimate potential additional resources from the 3D reflection seismic experiment on the order of10 Mt to be worth drilling for detailed assessments. The mineralization is crosscut by at leasttwo major sets of northwest-dipping reflections interpreted to dominantly be normal faults and to beresponsible for much of the lowland in the Blötberget area. Moreover, thesepost-mineralization faults likely control the current 3D geometry of the deposits. Curved andsubmerged reflections interpreted from folds or later intrusions are also observed, showing thegeological complexity of the study area. The seismic survey also delineates the near-surfaceexpression of a historical tailing as a by-product of refraction static corrections, demonstratingwhy 3D seismic data are so valuable for both mineral exploration and mine planning applications.

Abstract. Karst water resources play an important role in drinking water supply but arehighly vulnerable to even slight changes in climate. Thus, solid andspatially dense geological information is needed to model the response ofkarst hydrological systems to such changes. Additionally, environmentalinformation archived in lake sediments can be used to understand past climateeffects on karst water systems. In the present study, we carry out amulti-methodological geophysical survey to investigate the geologicalsituation and sedimentary infill of two karst lakes (Metzabok and Tzibaná)of the Lacandon Forest in Chiapas, southern Mexico. Both lakes present largeseasonal lake-level fluctuations and experienced an unusually sudden andstrong lake-level decline in the first half of 2019, leaving Lake Metzabok(maximum depth ∼25 m) completely dry and Lake Tzibaná (depth∼70 m) with a water level decreased byapprox. 15 m. Before this event, during a lake-level high stand inMarch 2018, we collected water-borne seismic data with a sub-bottom profiler(SBP) and transient electromagnetic (TEM) data with a newly developed floatingsingle-loop configuration. In October 2019, after the sudden drainage event,we took advantage of this unique situation and carried out complementarymeasurements directly on the exposed lake floor of Lakes Metzabok andTzibaná. During this second campaign, we collected time-domain inducedpolarization (TDIP) and seismic refraction tomography (SRT) data. Byintegrating the multi-methodological data set, we (1) identify 5–6 mthick, likely undisturbed sediment sequences on the bottom of both lakes,which are suitable for future paleoenvironmental drilling campaigns, (2)develop a comprehensive geological model implying a strong interconnectivitybetween surface water and karst aquifer, and (3) evaluate the potential of theapplied geophysical approach for the reconnaissance of the geologicalsituation of karst lakes. This methodological evaluation reveals that underthe given circumstances, (i) SBP and TDIP phase images consistently resolvethe thickness of the fine-grained lacustrine sediments covering the lakefloor, (ii) TEM and TDIP resistivity images consistently detect the upperlimit of the limestone bedrock and the geometry of fluvial deposits of a riverdelta, and (iii) TDIP and SRT images suggest the existence of a layer thatseparates the lacustrine sediments from the limestone bedrock and consists ofcollapse debris mixed with lacustrine sediments. Our results show that thecombination of seismic methods, which are most widely used for lake-bottomreconnaissance, with resistivity-based methods such as TEM and TDIP cansignificantly improve the interpretation by resolving geological units orbedrock heterogeneities, which are not visible from seismic data. Only the useof complementary methods provides sufficient information to developcomprehensive geological models of such complex karst environments

Abstract. In an effort to improve our understanding of the seismiccharacter of the crust beneath southeast Australia and how it relates tothe tectonic evolution of the region, we analyse teleseismic earthquakesrecorded by 24 temporary and 8 permanent broadband stations using thereceiver function method. Due to the proximity of the temporary stations toBass Strait, only 13 of these stations yielded usable receiver functions,whereas seven permanent stations produced receiver functions for subsequentanalysis. Crustal thickness, bulk seismic velocity properties, and internalcrustal structure of the southern Tasmanides – an assemblage of Palaeozoicaccretionary orogens that occupy eastern Australia – are constrained byH–κ stacking and receiver function inversion, which point to the following: a ∼ 39.0 km thick crust; an intermediate–high Vp/Vs ratio(∼ 1.70–1.76), relative to ak135; and a broad (> 10 km) crust–mantle transition beneath the Lachlan Fold Belt. These results areinterpreted to represent magmatic underplating of mafic materials at thebase of the crust. a complex crustal structure beneath VanDieland, aputative Precambrian continental fragment embedded in the southernmostTasmanides, that features strong variability in the crustal thickness (23–37 km) and Vp/Vs ratio (1.65–193), the latter of which likely representscompositional variability and the presence of melt. The complex origins ofVanDieland, which comprises multiple continental ribbons, coupled withrecent failed rifting and intraplate volcanism, likely contributes to theseobservations. stations located in the East Tasmania Terrane andeastern Bass Strait (ETT + EB) collectively indicate a crust of uniformthickness (31–32 km), which clearly distinguishes it from VanDieland to thewest.Moho depths are also compared with the continent-wide AusMoho model insoutheast Australia and are shown to be largely consistent, except inregions where AusMoho has few constraints (e.g. Flinders Island). A jointinterpretation of the new results with ambient noise, teleseismic tomography,and teleseismic shear wave splitting anisotropy helps provide new insightinto the way that the crust has been shaped by recent events, includingfailed rifting during the break-up of Australia and Antarctica and recentintraplate volcanism.