Seismo-acoustic analysis of Debris Flows events at the Illgraben catchment, Switzerland

2020 ◽  
Author(s):  
Giacomo Belli ◽  
Emanuele Marchetti ◽  
Fabian Walter ◽  
Brian McArdell
Keyword(s):  
Early Warning ◽  
Debris Flows ◽  
Seismic Waves ◽  
Acoustic Analysis ◽  
Flow Characteristics ◽  
Early Warning Systems ◽  
Seismic Signals ◽  
Turbulent Structures ◽  
Good Reliability ◽  
Mountain Environments

<p>Debris flows are episodic strongly impacting gravitational currents of generally high density, consisting of mixtures of water and debris in varying proportions and occurring in steep mountain torrents with volumes commonly exceeding thousands of m<sup>3</sup>. Despite the observation that debris flows are among the most dangerous processes in mountain environments, the moderate flow velocities (typically < 10 m/s) make early warning in principle possible if the flows are detected early upon formation.</p><p>Seismic and infrasound studies of debris flows rapidly increased in the last decade but focused mostly on event detectability and application as early-warning systems. Seismic networks, arrays of infrasound sensors and the combined use of a collocated single seismic and infrasound sensors, have turned out to be efficient systems for detecting the occurrence of debris flows in near-real time with a good reliability.</p><p>However, open questions remain about the possibility to infer source characteristics and event magnitude from recorded geophysical signals. This requires theoretical source models of elastic energy radiated both in the ground, in the form of seismic waves, and in the atmosphere, in the form of infrasound.  Seismic waves are believed to be generated by both large sediment particles impacts on the channel bed and by turbulent structures within the debris flow. Infrasound is instead believed to be generated by standing waves at the free surface of the flow, but their source processes are not yet fully understood.</p><p>Here we present preliminary results of a study performed at the Illgraben catchment (Switzerland), in the 2017-2019 period, combining infrasound and seismic signals with direct in-torrent measurements of flow depth and velocity. Seismic and infrasound signals are analyzed using both spectral analysis and array techniques, in order to achieve an improved understanding of the dynamics of the source mechanisms of the two wavefields. Comparison with in-situ measurements is used to extrapolate empirical relationships between signal features, e.g. amplitude, spectral content or waveform characteristics of both seismic signals and infrasound, and flow characteristics.</p><p>The results obtained will possibly be used to develop an efficient monitoring system for remote detection and the early warning of debris flows using seismic signals and infrasound generated by the process.</p>

scholarly journals Numerical Modeling of Infrasound Energy Radiation by Debris Flow Events

2021 ◽  
Author(s):  
M. Coco ◽  
E. Marchetti ◽  
O. Morandi
Keyword(s):  
Numerical Modeling ◽  
Debris Flow ◽  
Early Warning ◽  
Debris Flows ◽  
Flow Characteristics ◽  
Early Warning Systems ◽  
Numerical Results ◽  
Warning Systems ◽  
Simulation Code ◽  
Energy Radiation

AbstractDebris flows constitute a severe natural hazard in Alpine regions. Studies are performed to understand the event predictability and to identify early warning systems and procedures. These are based both on sensors deployed along the channels or on the amplitude of seismic and infrasound waves radiated by the flow and recorded far away. Despite being very promising, infrasound cannot be used to infer the source characteristics due to the lack of a physical model of the infrasound energy radiated by debris flows. Here the simulation of water flow along a simple channel is presented, experiencing the fall from a dam, performed within the open source simulation code OpenFOAM. The pressure perturbation within the atmosphere produced by the flow is extracted and the infrasound signature of the events as a function of the flow characteristics is defined. Numerical results suggest that infrasound is radiated immediately downstream of the dam with amplitude and period that scale with dam height and water level. Modeled infrasound waveform is interpreted as being produced mostly by waves at the water free surface developing downstream of the dam. Despite the effect of sediments is not considered in this first study and will be implemented in future investigations, numerical results obtained with this simple model are in general agreement with experimental results obtained from array analysis of infrasound data recorded at Illgraben, Switzerland. Results highlight how numerical modeling can provide critical information to define a source mechanism of infrasound energy radiation by debris-flow, that is required also to improve early warning systems.

A successful approach to earthquake early warning systems

Impact ◽  
2019 ◽  
Vol 2019 (9) ◽  
pp. 18-20
Author(s):  
Pei-Yang Lin
Keyword(s):  
Early Warning ◽  
Seismic Activity ◽  
Peak Ground Acceleration ◽  
Seismic Waves ◽  
Early Warning Systems ◽  
Blind Spot ◽  
Earthquake Early Warning ◽  
Primary Wave ◽  
Ground Acceleration ◽  
Sea Bed

The goal of an earthquake early warning system (EEW) is to identify where and when an earthquake has occurred and then warn those in danger. We think of earthquakes as happening instantaneously but from the detection of the initial event there is time until the effects are noticed. An early warning of even 6 to 19 seconds could allow sensitive infrastructure like factories or power plants to enact automated precautions, reducing damage and allowing for quicker recovery. Warnings of 30 seconds could prevent 95 per cent of potential mortalities in some large cities. It is exactly these crucial seconds that Lin is trying to provide. His team's work centres on developing an integrated EEW for Taiwan which, once proven effective, to help bring this system to other countries who live with the threat of seismic activity.<br/> The EEW developed by Lin works through detecting the seismic waves that earthquakes produce. When an earthquake strikes the ground shakes, this creates seismic waves that move through the earth. These waves, exactly like a ripple in a pond, move out from the epicentre. The first wave, known as the primary wave is low intensity and will not affect structures significantly. The secondary wave however arrives a bit later and causes the intense shaking, damage and casualties. "The goal of the system is to deploy onsite Earthquake Early Waring System(EEWS) to detect the seismic waves and provide warning for the neighborhoods," explains Lin. The regional detectors and EEWS can be deployed to monitor a whole country.<br/> For traditional regional EEWS,like Japan,once a wave is detected the information is sent to a central server which determines the epicentre of the quake, the magnitude of the earthquake and the peak ground acceleration, an important measure of earthquake intensity. "With these measurements the server can then predict where peak ground acceleration will exceed thresholds likely to cause damage and send the alarm," says Lin. The whole process takes only about 15 seconds, which is extremely valuable time for those further away from the epicentre, but because the wave can move up to 90km within these 15 seconds there is a blind spot of about 90km in the regional Earthquake Early Waring System. Lin points out that a blind spot of this size may be fine for some regions. "In Japan the epicentre of the typical hazardous earthquake is in the east sea bed about 100km from the shore but for Taiwan the epicentres are typically below a city. Therefore Lin has developed an integrated approach combining the regional EEW with onsite EEW. The onsite EEWS are installed in cities and monitor local seismic activity. They can predict peak ground acceleration for local area from the primary wave within 1 to 3 seconds and reduce the blind spot to 20 or 30km. Each system has its advantages and disadvantages but integration provides maximum coverage.

An early warning system for rainfall-triggered shallow slides and debris flows. Application in Catalonia, Spain and Canton of Bern, Switzerland

2020 ◽  
Author(s):  
Rosa M Palau ◽  
Marc Berenguer ◽  
Marcel Hürlimann ◽  
Daniel Sempere-Torres ◽  
Catherine Berger ◽  
...  
Keyword(s):  
Early Warning ◽  
Debris Flows ◽  
Risk Mitigation ◽  
Regional Scale ◽  
Slope Angle ◽  
Early Warning Systems ◽  
Warning Systems ◽  
Radar Rainfall ◽  
Susceptibility Maps ◽  
Landslide Event

&lt;p&gt;Risk mitigation for rainfall-triggered shallow slides and debris flows at regional scale is challenging. Early warning systems are a helpful tool to depict the location and time of future landslide events so that emergency managers can act in advance. Recently, some of the regions that are recurrently affected by rainfall triggered landslides have developed operational landslide early warning systems (LEWS). However, there are still many territories where this phenomenon also represents an important hazard and lack this kind of risk mitigation strategy.&lt;/p&gt;&lt;p&gt;The main objective of this work is to study the feasibility to apply a regional scale LEWS, which was originally designed to work over Catalonia (Spain), to run in other regions. To do so we have set up the LEWS to Canton of Bern (Switzerland).&lt;/p&gt;&lt;p&gt;The LEWS combines susceptibility maps to determine landslide prone areas and in real time high-resolution radar rainfall observations and forecasts. The output is a qualitative warning level map with a resolution of 30 m.&lt;/p&gt;&lt;p&gt;Susceptibility maps have been derived using a simple fuzzy logic methodology that combines the terrain slope angle, and land use and land cover (LULC) information. The required input parameters have been obtained from regional, pan-European and global datasets.&lt;/p&gt;&lt;p&gt;Rainfall inputs have been retrieved from both regional weather radar networks, and the OPERA pan-European radar composite. A set of global rainfall intensity-duration data has been used to asses if a rainfall event has the potential of triggering a landslide event.&lt;/p&gt;&lt;p&gt;The LEWS has been run in the region of Catalonia and Canton of Bern for specific rainfall events that triggered important landslides. Finally, the LEWS performance in Catalonia has been assessed.&lt;/p&gt;&lt;p&gt;Results in Catalonia show that the LEWS performance strongly depends on the quality of both the susceptibility maps and rainfall data. However, in both regions the LEWS is generally able to issue warnings for most of the analysed landslide events.&lt;/p&gt;

Multi-parametric observations of debris-flow initiation at the headwaters of the Gadria catchment (eastern Italian Alps)

2020 ◽  
Author(s):  
Velio Coviello ◽  
Matteo Berti ◽  
Lorenzo Marchi ◽  
Francesco Comiti ◽  
Giulia Marchetti ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Debris Flow ◽  
Early Warning ◽  
Debris Flows ◽  
Lead Time ◽  
Early Warning Systems ◽  
Force Balance ◽  
Italian Alps ◽  
Alarm Systems ◽  
Debris Flow Initiation

&lt;p&gt;The complete understanding of the mechanisms controlling debris-flow initiation is still an open challenge in landslide research. Most debris-flow models assume that motion suddenly begins when a large force imbalance is imposed by slope instabilities or the substrate saturation that causes the collapse of the channel sediment cover. In the real world, the initiation of debris flows usually results from the perturbation of the static force balance that retains sediment masses in steep channels. These perturbations are primarily generated by the increasing runoff and by the progressive erosion of the deposits. Therefore, great part of regional early warning systems for debris flows are based on critical rainfall thresholds. However, these systems are affected by large spatial-temporal uncertainties due to the inadequate number and distribution of rain gauges. In addition, rainfall analysis alone does not explain the dynamics of sediment fluxes at the catchment scale: short-term variations in the sediment sources strongly influence the triggering of debris flows, even in catchments characterized by unlimited sediment supply.&lt;/p&gt;&lt;p&gt;In this work, we present multi-parametric observations of debris flows at the headwaters of the Gadria catchment (eastern Italian Alps). In 2018, we installed a monitoring network composed of geophones, three soil moisture probes, one tensiometer and two rain-triggered videocameras in a 30-m wide steep channel located at about 2200 m a.s.l. Most sensors lie on the lateral ridges of this channel, except for the tensiometer and the soil moisture probes that are installed in the channel bed at different depths. This network recorded four flow events in two years, two of which occurred at night. Specifically, the debris flows that occurred on 21 July 2018 and 26 July 2019 produced remarkable geomorphic changes in the monitored channel, with up to 1-m deep erosion. For all events, we measured peak values of soil water content that are far from saturation (&lt;0.25 at -20 cm, &lt;0.15 at -40 cm, &lt;0.1 at -60 cm). We derived the time of occurrence and the duration of these events from the analysis of the seismic signals. Combining these pieces of information with data gathered at the monitoring station located about 2 km downstream, we could determine the flow kinematics along the main channel.&lt;/p&gt;&lt;p&gt;These results, although still preliminary, show the relevance of a multi-parametric detection of debris-flow initiation processes and may have valuable implications for risk management. Alarm systems for debris flows are becoming more and more attractive due the continuous development of compact and low-cost distributed sensor networks. The main challenge for operational alarm systems is the short lead-time, which is few tens of seconds for closing a transportation route or tens of minutes for evacuating settlements. Lead-time would significantly increase installing a detection system in the upper part of a catchment, where the debris flow initiates. The combination of hydro-meteorological monitoring in the source areas and seismic detection of channelized flows may be a reliable approach for developing an integrated early warning - alarm system.&lt;/p&gt;

scholarly journals All Types of Large Earthquakes Produce Prompt Gravity Signals

Eos ◽  
2019 ◽  
Vol 100 ◽  
Author(s):  
Terri Cook
Keyword(s):  
Early Warning ◽  
Seismic Waves ◽  
Early Warning Systems ◽  
Earthquake Early Warning ◽  
Warning Systems ◽  
Earthquake Early Warning Systems ◽  
Tectonic Settings ◽  
Large Earthquakes

New observations of recently discovered gravity perturbations that precede seismic waves have the potential to improve earthquake early-warning systems in California and other tectonic settings.

scholarly journals Technical notes: Rainfall threshold calculation for debris flow early warning in areas with scarcity of data

2017 ◽  
Author(s):  
Hua-li Pan ◽  
Yuan-jun Jiang ◽  
Jun Wang ◽  
Guo-qiang Ou
Keyword(s):  
Debris Flow ◽  
Early Warning ◽  
Debris Flows ◽  
Empirical Relationship ◽  
Early Warning Systems ◽  
Rainfall Threshold ◽  
Negative Slope ◽  
Observation Data ◽  
Flow Forming ◽  
Initiation Mechanism

Abstract. Debris flows are one of the natural disasters that frequently occur in mountain areas, usually accompanied by serious loss of lives and properties. One of the most used approaches to mitigate the risk associated to debris flows is the implementation of early warning systems based on well calibrated rainfall thresholds. However, many mountainous areas have little data regarding rainfall and hazards, especially in debris flow forming regions. Therefore, the traditional statistical analysis method that determines the empirical relationship between rainfall and debris flow events cannot be effectively used to calculate reliable rainfall thre-shold in these areas. To solve this problem, this paper developed a quantitative method to identify rainfall threshold for debris flow early warning in data-poor areas based on the initiation mechanism of hydraulic-driven debris flow. First, we studied the characteristics of the study area, including meteorology, hydrology, topography and physical characteristics of the loose solid materials. Then, the rainfall threshold was calculated by the initiation me-chanism of the hydraulic debris flow. The results show that the proposed rainfall threshold curve is a function of the antecedent precipitation index and 1-h rainfall. The function is a line with a negative slope. To test the proposed method, we selected the Guojuanyan gully, a typical debris flow valley that during the 2008–2013 period experienced several debris flow events and that is located in the meizoseismal areas of Wenchuan earthquake, as a case study. We compared the calculated threshold with observation data, showing that the accuracy of the method is satisfying and thus can be used for debris flow early warning in areas with scaricty of data.

Investigating infrasound sources within Illgraben debris-flows

2021 ◽  
Author(s):  
Giacomo Belli ◽  
Emanuele Marchetti ◽  
Fabian Walter ◽  
Brian McArdell ◽  
Małgorzata Chmiel ◽  
...  
Keyword(s):  
Debris Flow ◽  
Early Warning ◽  
Debris Flows ◽  
Fluid Dynamic ◽  
Flow Characteristics ◽  
Maximum Flow ◽  
Dynamic Processes ◽  
Flow Density ◽  
Small Aperture ◽  
Flow Monitoring

&lt;p&gt;Debris flows are episodic gravitational currents, consisting of mixtures of water and debris in varying proportions. They occur in steep mountain torrents with volumes commonly exceeding thousands of m&lt;sup&gt;3&lt;/sup&gt;. Given their unpredictability and their capability to transport large boulders, debris flows rank among the most dangerous natural hazards in mountain environments. Nevertheless, moderate flow velocities (typically &lt; 10 m/s) make early warning in principle possible if the flows are detected early upon formation.&lt;/p&gt;&lt;p&gt;Infrasound studies of debris flows increased significantly in the last decade, focusing mostly on event detectability and application for early-warning. The use of infrasound arrays and the combined use of collocated seismic and infrasound sensors have turned out to be efficient systems for reliable detection of debris flows in near-real time.&lt;/p&gt;&lt;p&gt;Despite these advances, open questions remain about the possibility to infer debris-flow source characteristics and event magnitude from recorded infrasonic signals. This requires theoretical and/or empirical source models describing elastic energy radiation in the atmosphere, in the form of infrasound, and relating it with fluid dynamic processes within a debris flow. Infrasound radiated by debris-flows is believed to be generated by standing waves that develop at the free surface of the flow, but details of the involved dynamic processes are not fully understood.&lt;/p&gt;&lt;p&gt;Here, we present the analysis of infrasonic signals recorded with a small aperture array during the 2017-2020 debris-flow seasons in the Illgraben catchment (Switzerland, Canton Valais), including more than 20 events of variable sizes. In order to better understand infrasound source mechanisms and to investigate the fluid dynamics processes involved in the infrasonic energy generation, debris-flow infrasound signals are quantitatively compared with independent hydraulic information of the flow (velocity, maximum flow depth and flow density). Finally, we discuss the use of extrapolated empirical relationships between infrasound signal features and flow characteristics for debris-flow monitoring and risk management.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

scholarly journals Rainfall threshold calculation for debris flow early warning in areas with scarcity of data

2018 ◽  
Vol 18 (5) ◽  
pp. 1395-1409 ◽  
Author(s):  
Hua-Li Pan ◽  
Yuan-Jun Jiang ◽  
Jun Wang ◽  
Guo-Qiang Ou
Keyword(s):  
Debris Flow ◽  
Wenchuan Earthquake ◽  
Early Warning ◽  
Debris Flows ◽  
Early Warning Systems ◽  
Rainfall Threshold ◽  
Warning Systems ◽  
Mountainous Areas ◽  
Rainfall Thresholds ◽  
Initiation Mechanism

Abstract. Debris flows are natural disasters that frequently occur in mountainous areas, usually accompanied by serious loss of lives and properties. One of the most commonly used approaches to mitigate the risk associated with debris flows is the implementation of early warning systems based on well-calibrated rainfall thresholds. However, many mountainous areas have little data regarding rainfall and hazards, especially in debris-flow-forming regions. Therefore, the traditional statistical analysis method that determines the empirical relationship between rainstorms and debris flow events cannot be effectively used to calculate reliable rainfall thresholds in these areas. After the severe Wenchuan earthquake, there were plenty of deposits deposited in the gullies, which resulted in several debris flow events. The triggering rainfall threshold has decreased obviously. To get a reliable and accurate rainfall threshold and improve the accuracy of debris flow early warning, this paper developed a quantitative method, which is suitable for debris flow triggering mechanisms in meizoseismal areas, to identify rainfall threshold for debris flow early warning in areas with a scarcity of data based on the initiation mechanism of hydraulic-driven debris flow. First, we studied the characteristics of the study area, including meteorology, hydrology, topography and physical characteristics of the loose solid materials. Then, the rainfall threshold was calculated by the initiation mechanism of the hydraulic debris flow. The comparison with other models and with alternate configurations demonstrates that the proposed rainfall threshold curve is a function of the antecedent precipitation index (API) and 1 h rainfall. To test the proposed method, we selected the Guojuanyan gully, a typical debris flow valley that during the 2008–2013 period experienced several debris flow events, located in the meizoseismal areas of the Wenchuan earthquake, as a case study. The comparison with other threshold models and configurations shows that the selected approach is the most promising starting point for further studies on debris flow early warning systems in areas with a scarcity of data.

The CARE Telematics Network for the Surveillance of Influenza in Europe

1995 ◽  
Vol 34 (05) ◽  
pp. 518-522 ◽  
Author(s):  
M. Bensadon ◽  
A. Strauss ◽  
R. Snacken
Keyword(s):  
Public Health ◽  
Early Warning ◽  
Early Warning Systems ◽  
Warning Systems ◽  
Surveillance Networks ◽  
Spanish Flu ◽  
The 1950S ◽  
National Networks ◽  
First Time

Abstract:Since the 1950s, national networks for the surveillance of influenza have been progressively implemented in several countries. New epidemiological arguments have triggered changes in order to increase the sensitivity of existent early warning systems and to strengthen the communications between European networks. The WHO project CARE Telematics, which collects clinical and virological data of nine national networks and sends useful information to public health administrations, is presented. From the results of the 1993-94 season, the benefits of the system are discussed. Though other telematics networks in this field already exist, it is the first time that virological data, absolutely essential for characterizing the type of an outbreak, are timely available by other countries. This argument will be decisive in case of occurrence of a new strain of virus (shift), such as the Spanish flu in 1918. Priorities are now to include other existing European surveillance networks.

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