Jaime Checa’s Post

From overcoming difficult field conditions to obtaining beautiful subsurface seismic images😀 A small highlight from one of our ambitious seismic imaging projects at Wits Seismic Research Centre. This is probably one of our best seismic data acquired using our 500 kg drophammer (attached on the bobcat) in a hardrock environment. Surprisingly, the data were acquired on some thick sand cover (~20-150 m in thickness, figure on the left) and yet we managed to image the subsurface structures down to about 3.5 km depth below ground surface!! (we acquired several profiles, only showing one here). No detailed processing done, just a quick 1st pass look but we already see some beautiful P-wave reflections, slightly disturbed by some faulting on the migrated stack. Such beauty 💙- yes, seismic energy can penetrate that deep even from a 500 kg drophammer. Wits School of Geosciences R.T. Clark Co., Inc :: Geophysical Equipment University of the Witwatersrand

Join EEGS for the May TAG webinar “Passive Seismic Approaches for Active Geophysicists” Tuesday, May 28, 2024 Register at: https://lnkd.in/ez5JvE4D Resonance frequencies are intrinsic properties of elastic media: they depend on their stiffness and mass distribution, and on their constraints.  In geological and geophysical applications, resonance frequencies are traditionally assessed by means of the microtremor H/V seismic method.  Resonance frequencies can quite easily be converted into the corresponding depths of seismic reflectors responsible for the occurrence of those resonances, in the presence of a Vs estimate. Since 1999, this has led to several interesting images of the main reflectors in the soil achieved by means of passive single station approaches.  However, resonances, being intrinsic properties, are expected to change only in amplitude and not in frequency with the measurement point, in a same medium. "How can we reconcile the fact that, as an example, a basin cross-section is a geological medium with characteristic and unique modal frequencies that do not change along the cross-section, with the fact that the H/V peak frequencies shift from the sides to the center of the basin? To answer this question, we’ll explore what we call 1D and 2D resonance and H/V or H&V approaches and provide some hints on how to discriminate and exploit the two cases.

Join EEGS for the May TAG webinar “Passive Seismic Approaches for Active Geophysicists”  Tuesday, May 28, 2024  Register at: https://lnkd.in/ez5JvE4D Resonance frequencies are intrinsic properties of elastic media: they depend on their stiffness and mass distribution, and on their constraints.  In geological and geophysical applications, resonance frequencies are traditionally assessed by means of the microtremor H/V seismic method.  Resonance frequencies can quite easily be converted into the corresponding depths of seismic reflectors responsible for the occurrence of those resonances, in the presence of a Vs estimate. Since 1999, this has led to several interesting images of the main reflectors in the soil achieved by means of passive single station approaches.  However, resonances, being intrinsic properties, are expected to change only in amplitude and not in frequency with the measurement point, in a same medium. "How can we reconcile the fact that, as an example, a basin cross-section is a geological medium with characteristic and unique modal frequencies that do not change along the cross-section, with the fact that the H/V peak frequencies shift from the sides to the center of the basin? To answer this question, we’ll explore what we call 1D and 2D resonance and H/V or H&V approaches and provide some hints on how to discriminate and exploit the two cases. 

𝗦𝗵𝗼𝘂𝗹𝗱 𝗩𝗲𝗿𝘁𝗶𝗰𝗮𝗹 𝗦𝗲𝗶𝘀𝗺𝗶𝗰 𝗣𝗿𝗼𝗳𝗶𝗹𝗲𝘀 (𝗩𝗦𝗣𝘀) 𝗯𝗲 𝘂𝘀𝗲𝗱 𝗶𝗻 𝗰𝗮𝗿𝗯𝗼𝗻 𝘀𝘁𝗼𝗿𝗮𝗴𝗲? The question might seem to be bait, but we ask it sincerely in our latest Canadian Society of Exploration Geophysicists - CSEG RECORDER article. For context, I and my co-authors, Eric Street, Graham Hack, Jason Schweigert, and Matthew Allen suggest in our #Theseus and #24D carbon storage MMV methods that VSPs are not generally needed in onshore commercial carbon storage. Carbon Alpha's Theseus 24D enters the fray of reducing seismic costs in monitoring through changes in imaging areas, the integration of 2D and 3D seismic, and the jettisoning of techniques that are not required through the long life of these projects. The aim is similar to sparse nodal techniques but preserves the continuous imaging of 2D and 3D seismic. And one of the techniques we 'Jettison' is VSP surveying. Our suggestion is likely upsetting on the first read, because VSPs do have great value. They are used heavily in pilots, and have a history of use in Western Canada and the world. At presentations at GeoConvention Partnership and Carbon Capture Canada this year, we know we stirred some controversy by making these suggestions. But science is about challenging ideas and learning, so we wanted to follow up on the controversy and discuss the question of VSPs in commercial scale carbon storage in greater detail. This led to our Recorder article, which can be found here: https://lnkd.in/gMMKERxS Please have a look at the article. Our advice is far from as hard and fast as the few words in this post make it seem.

This week, as we celebrate Geophysics Day from Argentina, we extend our congratulations to all professionals in this exciting and valuable field of science. We also take this opportunity to invite you to join us for the April session of our 2024 webinar series titled "Shaping Your Seismic": Exploring Exclusion Zones in PaleoScan with Jake Marson. 🔗 Register >> https://lnkd.in/exTQ6WnP #subsurface #geoscience #geophysics

New paper as a co-author. Akamatsu et al. (2025, Tectonophysics) "Mesoscale fractures control the scale dependences of seismic velocity and fluid flow in subduction zones" Journal link: https://lnkd.in/gFE-Z5kV Abstract: Natural geological systems contain porosity structures of various scales that play different roles in geophysical properties, fluid flow, and geodynamics. To understand seismic activity associated with high pore-fluid pressure and fluid migration in subduction zones, it is necessary to explore the scale dependence of geophysical properties such as seismic velocity and permeability. Here, we compare laboratory-measured ultrasonic velocity measured on core samples from the Susaki area in the Shimanto accretionary complex, SW Japan, with sonic velocity measured by borehole logging experiments. Results show that P-wave velocity decreases from the laboratory (∼6 km/s) to the borehole scales (∼5 km/s). This scale-variant effect can be explained by a differential effective medium model whereby mesoscale porosity that is undetectable at the ultrasonic wavelength is introduced into the matrix phase with microscale porosity. Assuming typical apertures for micro- and mesoscale fractures, we estimate that the effective permeability can increase to 10^−12 – 10^−11 m^2 with increasing in the mesoscale porosity and decreasing P-wave velocity down to 4–5 km/s. These results indicate that seismic velocity anomalies and related seismic activity are associated with the presence of mesoscale fractures in subduction zones.

Although I am not at ASEG Discover in Hobart myself, I am excited for the presentation today on “A Novel yet Simple Approach to the Interpretation of HVSR Data in Australia – A Data Rich Case Study from the Pilbara” that I co-authored with Nathan Tabain from BHP. In this work, which is based on a dataset of ~3,400 short-duration 3C passive seismic recordings, Nathan will discuss how not peaks, but resonance troughs were used for interpretation. Indeed, the trough horizon was easier to interpret, had better along-line and across-line continuity, and more vertical variability than the corresponding peak horizon at half the trough frequency. Nathan will bring the proverbial kitchen sink and show how these data correlated, rather spectacularly, with several independent apriori datasets (airborne geophysics and drilling) and interpretations. Extended abstract: https://lnkd.in/d6uFkS8D. Presentation: Thu. 17/10 at 12 noon. Thanks to Alejandro Sanchez and others in the Southern Geoscience Consultants Near Surface team for their processing support, and Aaron Mullineux and crew for the efficient and safe aquisition of the data. The resonance trough example below is from Chandler and Lively (2014): Evaluation of the horizontal-to-vertical spectral ratio (HVSR) passive seismic method for estimating the thickness of quaternary deposits in Minnesota and adjacent parts of Wisconsin. Minnesota Geological Survey, OFR14-01.

Do you want to know the most Common challenges faced when processing seismic data acquired in desert environments ? Take look what's Sir Eamonn Murray Senior Processing Geophysicist is talking about. #Challenge 1: Time distortions and Reverberating noise. #Challenge 2: Intricacies in the near surface in desert regions. #Challenge 3: Multiple contaminations and velocities in the subsurface ... I will let you know a others in comments.

Excited to share that our work “Smart DAS Uphole Acquisition System: Bridging the Gap Between Surface Seismic and Borehole Geophysics” has been published in the upcoming AGU/Wiley Monograph: Distributed Acoustic Sensing in Borehole Geophysics. Editors: Yingping LI, Robert Mellors, Ge Zhan ISBN: 978-1-394-17924-4 | Publication Date: December 2024 Our innovative system integrates shallow DAS-enabled vertical arrays, improving seismic imaging by enhancing signal-to-noise ratios and reducing flow noise, offering a scalable and cost-effective solution for onshore reservoir monitoring and gas storage. 📚 Pick up a flyer at AGU 2024 or visit the link for more details: 🔗 AGU/Wiley Publication Details 📚 Learn more about TCCS: #DAS #SeismicImaging #BoreholeGeophysics #GeoH2 #SeismicMonitoring #EnergyTransition

Your Essential Toolkit for Navigating Seismic Data 💥 See below Elias' expert insight in to our growing geophysics domain in the 24.3 release of #tNavigator. “Our commitment to listening to client needs continues to drive innovation. With each release, tNavigator’s Seismic Interpretation solution strengthens its foundation, making workflows smoother and more efficient. Recent highlights include seamless merging of seismic horizons, greater integration for accurate, continuous interpretations, enhanced horizon editing tools and optimised data management. Our Seismic workspace keeps getting better and better!” If you would like to find out more, please get in touch and one of our experts would be more than happy to help! 📩 asktNav@rfdyn.com #Seismic #MakingThingsHappen #ReadyWhenYouAre