BCGS Technical Talks: Dan Hollis скачать в хорошем качестве

BCGS Technical Talks: Dan Hollis

Ambient seismology (also known as “passive seismic”) has been around for since the earliest seismoscope was invented by the Chinese philosopher Chang Heng in A.D. 132, if you consider primitive earthquake detection and localization as the earliest example of the science. Since those early times, the science has progressed using more sophisticated equipment, advances in data analyses methods, and with the introduction of high-performance computing. Beyond earthquake detection and localization, there have been developed a range of ambient seismology methods used to the study the interior of the Earth: from travel-time tomography to image the Earth’s interior to near-surface mapping of cover using horizontal-to-vertical spectral ratio (HVSR) analysis. A recent addition to the ambient seismology toolkit is ambient noise tomography (ANT) which will be the focus of this presentation. Early ANT work started in the early 2000s using global and regional seismic networks and was used for deep imaging from crust to core. With the introduction of inexpensive 1-component nodal seismometers in the early 2010s ANT started being used for imaging of the upper crust and near-surface, mainly producing Vs imaging using Rayleigh wave tomography where velocity is a proxy for lithology and structure. Application of the ANT method for mineral exploration started in the mid-2010s using Rayleigh wave straight ray tomography. The introduction of 3-component nodal seismometers in the late 2010s and early 2020s allowed ANT imaging using both Rayleigh and Love wave which improved imaging accuracy, and also provided the basic seismic data that enabled other passive seismic methods such as receiver functions, HVSR, accurate seismicity localization, and local earthquake tomography from one common data set. Since ANT’s introduction in the mineral exploration toolkit, there have been improvements in survey design and data processing workflow that have steadily improve its usefulness. There are processes developed to improve ANT imaging or extract additional imaging products from the ANT processing workflow that either are not commonly used or has not been use in ANT mineral exploration. A couple of examples of these developments are extracting anisotropy information, use of different tomography methods (e.g. raypath or eikonal tomography) as an alternative to straight ray tomography, and use of reflected surface waves to enhance imaging of near-vertical structures. This presentation will present a brief review of the ANT method and the current state of its use. The second part of this presentation will review the newer developments mentioned above and how they might be employed in ANT surveys conducted for mineral exploration.