Abstract
Summary Seismic attenuation measurements, especially those obtained from coda decay analysis, are becoming a key data source for the characterization of the heterogeneous Earth due to their sensitivity to small-scale heterogeneities. However, the relation between the scattering attenuation measured from coda waves and physical rock properties is still unclear. The goal of this study is to identify the main petrophysical and mineralogical factors controlling coda attenuation in volcanic rocks at the laboratory scale, as a necessary step before modelling seismic waves in real volcanic media. Coda wave attenuation was estimated from ultrasonic S-wave waveforms. To quantify the heterogeneity of the rocks and link them with this attenuation parameter, we performed several categorizations of the pore and grain systems of volcanic samples. Considering that seismic attenuation in rock samples can be modelled using the framework of wave propagation in random media, a statistical analysis of shear-wave velocity fluctuations was performed: this analysis gives correlation lengths ranging from 0.09 mm to 1.20 mm, which represents the length scale of heterogeneity in the samples. The individual evaluation of the pore space and mineral content revealed that the pores of the samples (characterized by large vesicles) have a bigger effect than the grains on the heterogeneity level. We have developed a framework where intrinsic properties of the host rocks drive seismic attenuation by correlating the petro-mineralogical characteristics obtained from image data processing and analysis, with the coda attenuation measured at ultrasonic frequencies. There is conclusive evidence that porosity alone is not the primary controller of coda attenuation: it is also changed by the alteration level (i.e. oxidation, coating of the vesicles, secondary minerals) and the size of grains and pores. Among all the parameters analysed, it appears that the pore space topology is the main contributor to scattering attenuation in the volcanic samples.
| Original language | English |
|---|---|
| Pages (from-to) | 1858-1872 |
| Number of pages | 15 |
| Journal | Geophysical Journal International |
| Volume | 226 |
| Issue number | 3 |
| Early online date | 22 May 2021 |
| DOIs | |
| Publication status | Published - 22 May 2021 |
Bibliographical note
ACKNOWLEDGEMENTSWe thank Dr John Millett (Volcanic Basin Petroleum Research VBPR) for providing the rock samples, Dr Maxim Lebedev (Curtin University) for helping us with the acquisition of the µCT images, and Prof Andrew Putnis for his insights in the mineralogical description of the samples. We also thank the Aberdeen-Curtin Alliance (http://aberdeencurtinalliance.org/) for providing funding for this research. Part of this study was undertaken using the TIMA instrumentation (ARC LE140100150) at the John de Laeter Center, Curtin University. This work was supported by resources provided by the Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia.
DATA AVAILABILITY
The data underlying this paper are available in Mendeley Data, at http://dx.doi.org/10.17632/ysmt4kcjtn.2. Results-related data are available in the paper and its online supplementary material.
Keywords
- Imageprocessing
- Codawaves
- Seismicattenuation
- Wave scattering and diffraction
- Microstructures