Ambient vibration characterization and monitoring of a rock slope close to collapse

Burjánek, Jan; Gischig, Valentin; Moore, Jeffrey R.; Fäh, Donat

doi:10.1093/gji/ggx424

Cited by 58 publications

(85 citation statements)

References 24 publications

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“…We are not aware of any other rock site presenting so high amplification levels. However, since comparable amplification levels (factors of 35) were previously observed at another rock slope instability (Preonzo, Burjánek et al 2017), we suggest that this phenomenon might be not rare for instabilities close to collapse. Fig.…”

Section: Discussionsupporting

confidence: 84%

“…6, the SRSR curves from 2014 (labeled with GON1-…) and 2015 (labeled with GON2-…) are plotted together. One can see that the dynamic behavior did not significantly change, and the measurements with 1-year time gap correspond very well (Bottelin et al 2013;Burjánek et al 2017), the re-measurement in 2015 was taken in very similar meteorological conditions as in 2014. The seismic activity was particularly low in the vicinity of the site in between June 2014 and June 2015 (no events of M > 2 within an epicentral distance of 20 km, no events of M > 3 within an epicentral distance of 60 km).…”

Section: Resultssupporting

confidence: 52%

“…GON201 is the most upper station (within the sliding area) with a polarization azimuth of around 50°, GON102 around 40° and GON101 around 20-30°. The main direction of ground motion polarization is usually parallel to the slope deformation (e.g., Burjánek et al 2010Burjánek et al , 2017. Therefore, the slightly rotating strike angle could indicate that the rock-slide movement is not linear in the area of the three stations, but contains a rotation.…”

Section: Resultsmentioning

confidence: 99%

“…The recording time for all measurements was 90 min, and the data acquisition was done with a digital recording unit coupled to Lennartz 3D seismometer with an eigenperiod of 1 s. The frequency band of interest lies only up to 20 Hz considering the minimum scales (wavelengths) of interest on the order of 10-50 m. This estimate originates from an empirical observation that the response usually becomes highly variable for frequencies above 20 Hz for an interstation distance of this order (tens of meters). It was observed in the past that the seismic response is sensitive to the meteorological conditions, especially during freezing periods (Bottelin et al 2013;Burjánek et al 2017). …”

Section: Methodsmentioning

confidence: 99%

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On the seismic response of instable rock slopes based on ambient vibration recordings

Kleinbrod

Burjánek

Fäh

2017

Earth Planets Space

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Rock slope failures can lead to huge human and economic loss depending on their size and exact location. Reasonable hazard mitigation requires thorough understanding of the underlying slope driving mechanisms and its rock mass properties. Measurements of seismic ambient vibrations could improve the characterization and detection of rock instabilities since there is a link between seismic response and internal structure of the unstable rock mass. An unstable slope near the village Gondo has been investigated. The unstable part shows strongly amplified ground motion with respect to the stable part of the rock slope. The amplification values reach maximum factors of 70. The seismic response on the instable part is highly directional and polarized. Re-measurements have been taken 1 year later showing exactly the same results as the original measurements. Neither the amplified frequencies nor the amplification values have changed. Therefore, ambient vibration measurements are repeatable and stay the same, if the rock mass has not undergone any significant change in structure or volume, respectively. Additionally, four new points have been measured during the re-measuring campaign in order to better map the border of the instability.

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Section: Discussionsupporting

confidence: 84%

Section: Resultssupporting

confidence: 52%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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On the seismic response of instable rock slopes based on ambient vibration recordings

Kleinbrod

Burjánek

Fäh

2017

Earth Planets Space

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“…Other potential changes in media (i.e., of the seismic response) are neither expected nor have been observed on the timescales of the ambient vibration experiments (Kleinbrod et al, ). Moreover, the site response at one such fractured slope has been observed to be linear over the measured range of weak input motions spanning two orders of magnitude (Burjánek et al, ), that is the response was the same for both ambient vibrations (0.8 μm peak‐to‐peak displacement) and earthquakes (up to 127 μm). This strongly supports the validity of models which adopt linear media.…”

Section: Model Of Media Containing Macroscopic Compliant Fracturesmentioning

confidence: 99%

Modeling the Seismic Response of Unstable Rock Mass With Deep Compliant Fractures

2019

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An experimental quantification of the strength and volume of real, heterogeneous, fractured rock masses is crucial when assessing rock slope stability. In order to quantitatively characterize the internal structure of fractured rock slopes, we present three‐dimensional numerical simulations of seismic wave propagation and compare with observations. We introduce a simple, effective model for fractured rock mass, which can easily be applied to simulate weak‐motion seismic wave propagation. The macroscopic compliant fractures cutting the rock mass are modeled as finite‐width zones of reduced elastic parameters characterized by shear and normal stiffness. The widths of such zones are not fixed and can be adjusted to fit the grid step in the numerical method. The proposed rock mass model is applied and tested for the Walkerschmatt site in southwest Switzerland. Synthetic ambient vibrations are generated using a finite‐difference method for the fractured rock mass, shaped by the real terrain geometry, and compared with the measurements. The observed seismic response is satisfactorily reproduced in a broad frequency range (0.5–10 Hz). The synthetized response is primarily controlled by the stiffness, depth, number of fractures, and inertial mass of the fractured rock. The simulated amplification and ground‐motion directionality correspond with the observed levels, unless (1) the simplified cracks reach depths of 200–300 m; and (2) the fracture network is larger with respect to the mapped network. This illustrates the potential of ambient vibration methods in combination with numerical simulations to infer depth, volume, and mechanical characteristics of slope instability.

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Seismic constraints on rock damaging related to a failing mountain peak: the Hochvogel, Allgäu

Dietze

Krautblatter²,

Illien

et al. 2020

Earth Surf Processes Landf

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Large rock slope failures play a pivotal role in long‐term landscape evolution and are a major concern in land use planning and hazard aspects. While the failure phase and the time immediately prior to failure are increasingly well studied, the nature of the preparation phase remains enigmatic. This knowledge gap is due, to a large degree, to difficulties associated with instrumenting high mountain terrain and the local nature of classic monitoring methods, which does not allow integral observation of large rock volumes. Here, we analyse data from a small network of up to seven seismic sensors installed during July–October 2018 (with 43 days of data loss) at the summit of the Hochvogel, a 2592 m high Alpine peak. We develop proxy time series indicative of cyclic and progressive changes of the summit. Modal analysis, horizontal‐to‐vertical spectral ratio data and end‐member modelling analysis reveal diurnal cycles of increasing and decreasing coupling stiffness of a 260,000 m3 large, instable rock volume, due to thermal forcing. Relative seismic wave velocity changes also indicate diurnal accumulation and release of stress within the rock mass. At longer time scales, there is a systematic superimposed pattern of stress increased over multiple days and episodic stress release within a few days, expressed in an increased emission of short seismic pulses indicative of rock cracking. Our data provide essential first order information on the development of large‐scale slope instabilities towards catastrophic failure. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

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Ambient vibration characterization and monitoring of a rock slope close to collapse

Cited by 58 publications

References 24 publications

On the seismic response of instable rock slopes based on ambient vibration recordings

On the seismic response of instable rock slopes based on ambient vibration recordings

Modeling the Seismic Response of Unstable Rock Mass With Deep Compliant Fractures

Seismic constraints on rock damaging related to a failing mountain peak: the Hochvogel, Allgäu

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