Locating rock slope failures along highways and understanding their physical processes using seismic signals

• Main Authors: J.-M. Chang, W.-A. Chao, H. Chen, Y.-T. Kuo, C.-M. Yang
• Format: Article
• Language: English
• Published: Copernicus Publications 2021-06-01
• Series: Earth Surface Dynamics
• Online Access: https://esurf.copernicus.org/articles/9/505/2021/esurf-9-505-2021.pdf
• ISSN: 2196-6311; 2196-632X

<p>Regional monitoring of rock slope failures using the seismic technique is rarely undertaken due to significant source location errors; this method also still lacks the signal features needed to understand events of this type because of the complex mass movement involved. To better comprehend these types of events, 10 known events along highways in Taiwan were analyzed. First, a hybrid method (GeoLoc) composed of cross-correlation-based and amplitude-attenuation-based approaches was applied, and it produced a maximum location error of 3.19 <span class="inline-formula">km</span> for the 10 events. We then analyzed the ratio of local magnitude (<span class="inline-formula"><i>M</i>_L</span>) and duration magnitude (<span class="inline-formula"><i>M</i>_D</span>) and found that a threshold of 0.85 yields successful classification between rock slope failure and earthquake. Further, GeoLoc can retrieve the seismic parameters, such as signal amplitude at the source (<span class="inline-formula"><i>A</i>₀</span>) and <span class="inline-formula"><i>M</i>_L</span> of events, which are crucial for constructing scaling law with source volume (<span class="inline-formula"><i>V</i></span>). Indeed, <span class="inline-formula">Log(<i>V</i>)</span> <span class="inline-formula">=</span> 1.12 <span class="inline-formula"><i>M</i>_L</span> <span class="inline-formula">+</span> 3.08 and <span class="inline-formula"><i>V</i></span> <span class="inline-formula">=</span> 77 290 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi>A</mi><mn mathvariant="normal">0</mn><mn mathvariant="normal">0.44</mn></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="bbe2ff3286b8731e8c9c326689d0b922"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="esurf-9-505-2021-ie00001.svg" width="25pt" height="17pt" src="esurf-9-505-2021-ie00001.png"/></svg:svg></span></span> derived in this study provide the lower bound of volume estimation, as the seismic parameters based on peak amplitudes cannot represent the full process of mass loss. Second, while video records correspond to seismic signals, the processes of toppling and sliding present column- and V-shaped spectrograms, respectively. The impacts of rockfall link directly to the pulses of seismic signals. Here, all spectrogram features of events can be identified for events with volumes larger than 2000 <span class="inline-formula">m³</span>, corresponding to the farthest epicenter distance of <span class="inline-formula">∼</span> 2.5 <span class="inline-formula">km</span>. These results were obtained using the GeoLoc scheme for providing the government with rapid reports for reference. Finally, a recent event on 12 June 2020 was used to examine the GeoLoc scheme's feasibility. We estimated the event's volume using two scalings: 3838 and 3019 <span class="inline-formula">m³</span>. These values were roughly consistent with the volume estimation of 5142 <span class="inline-formula">m³</span> from the digital elevation model. The physical processes, including rockfall, toppling, and complex motion behaviors of rock interacting with slope inferred from the spectrogram features were comprehensively supported by the video record and field investigation. We also demonstrated that the GeoLoc scheme, which has been implemented in Sinwulyu catchment, Taiwan, can provide fast reports, including the location, volume, and physical process of events, to the public soon after they occur.</p>