Good Vibrations

I compare some interesting aspects of Astronomy and Seismic Exploration. The most obvious differences related to the scale of observations, and the fact that astronomers rely upon 'passive' measurements and geophysicists typically create their own 'active' sources of energy. Both pursuits must overcome incredibly weak signal strengths, and both deploy a variety of sensors in creative ways to enhance the level of information in their data. Mapping the Heavens In this photo a camera in a fixed location takes a beautiful photo of the heavens on a clear night. In the background you can see a radio telescope dish pointing upwards. By precise mechanical control, such a dish can scan the sky, and accounting for the rotation of the earth, can also produce an image of the heavens – but over the range of frequencies and wavelengths corresponding to radio waves, rather than corresponding to visible light. As we will see, the resolution and insights gained by geophysicists deserve ...

I summarize and highlight elements of a large-scale multi-year experiments that quantified the impacts of exposure to a commercial seismic source on both an assemblage of tropical demersal fishes and pearl oysters targeted by commercial fisheries on the North West Shelf of Western Australia. Multiple lines of evidence suggest that seismic surveys have little impact on demersal fishes or pearl oysters in realistic environments.   The NWSSRP Study and the Marine Seismic Noise Measurement and Impact Theme In 2017, the Australian Institute of Marine Science (AIMS) and its partners commenced the North West Shoals to Shore Research Program (NWSSRP) , a three year, A$20 million study of the North West Shelf of Australia (refer to Figure 1). The program of 11 separate studies within four main themes has been conducted by a multidisciplinary team of scientists, technical staff and industry experts. Each of the four themes addressed gaps in scientific knowledge relevant to the environmental ...

I briefly illustrate how the propagation of seismic wavefields through the subsurface can lead to 'shadow zones' of imperfect seismic image quality. Using the foundation of image domain Least Squares Migration (LSM) introduced in previous articles, I also illustrate how shadow zones can be largely resolved. The Origin of Shadow Zones in Seismic Snapshots of a seismic wavefront as it propagates through a salt body. a) t = 6.7 seconds, b) t = 6.9 seconds, c) t = 7.2 seconds, and d) t = 7.5 seconds. The shot is located at x = 37000 ft. Shadow zones (refer to the next figure) correspond to ‘dim’ parts of the wavefront. From " Imaging by wave-equation inversion ", PhD thesis, Alejandro Valenciano (2008). The figure above shows four seismic wavefront snapshots as the wavefront propagates through a salt body. It should be obvious that the focusing and defocusing of such wavefronts as they propagate through complex geological features such as salt will result in some parts of...

The previous article in this two part series (" Least Squares Migration: 1 of 2 Articles ") discussed important similarities and distinctions between RTM (Reverse Time Migration), LS-RTM (Least Squares RTM), and FWI (Full Waveform Inversion). It was noted that traditionally, LSM does not update the velocity model. The discussion here describes an elegant process to recover high-resolution subsurface models of reflectivity, velocity and relative density from marine shot gathers with minimal pre-processing applied. The description here avoids mathematics and highlights the key breakthroughs that have enabled conventional FWI and data domain (LS-RTM to evolve into a methodology that can simultaneously recover several models of subsurface properties without significant leakage between parameters, make no assumptions about rock physics relationships, and bypass traditionally cascaded processing and imaging flows. Introduction Full Waveform Inversion (FWI) is a topic published and ...

I was inspired to write this short note by an online course by The Great Courses  that provided a few interesting insights into the process of decision making. The course uses many case studies to provide tangible insights into the myriad issues involved in the decision making processes in complex organisations. A key aspect of the lessons was an understanding how catastrophic errors can arise in decisions, and the post-mortems of such failures provide quite powerful insights into the interplay of the many issues involved.  Decisions by groups or individuals can be difficult to understand. Take for example, the countless failed investments in the airline business. The world would be very different without cheap and convenient airline travel, yet as a commercial enterprise the investment in airlines has generally been a disaster. A couple of quotes reinforce the point: It can be observed that the seismic service company business is not dissimilar to the airline business in a fe...