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Early magnitude estimation for the MW7.9 Wenchuan earthquake using progressively expanded P-wave time window.

Peng C, Yang J, Zheng Y, Xu Z, Jiang X - Sci Rep (2014)

Bottom Line: This information would have been available 40 s after the earthquake origin time and could have been refined in the successive 20 s using data from more distant stations.The reason for the magnitude underestimation is in part a combined effect of high-pass filtering and frequency dependence of the main radiating source during the rupture process.Finally we suggest only using Pd alone for magnitude estimation because of its slight magnitude saturation compared to the τc magnitude.

View Article: PubMed Central - PubMed

Affiliation: Institute of Geophysics, China Earthquake Administration, No. 5 Minzudaxue South Road, Haidian District, Beijing 100081, China.

ABSTRACT
More and more earthquake early warning systems (EEWS) are developed or currently being tested in many active seismic regions of the world. A well-known problem with real-time procedures is the parameter saturation, which may lead to magnitude underestimation for large earthquakes. In this paper, the method used to the MW9.0 Tohoku-Oki earthquake is explored with strong-motion records of the MW7.9, 2008 Wenchuan earthquake. We measure two early warning parameters by progressively expanding the P-wave time window (PTW) and distance range, to provide early magnitude estimates and a rapid prediction of the potential damage area. This information would have been available 40 s after the earthquake origin time and could have been refined in the successive 20 s using data from more distant stations. We show the suitability of the existing regression relationships between early warning parameters and magnitude, provided that an appropriate PTW is used for parameter estimation. The reason for the magnitude underestimation is in part a combined effect of high-pass filtering and frequency dependence of the main radiating source during the rupture process. Finally we suggest only using Pd alone for magnitude estimation because of its slight magnitude saturation compared to the τc magnitude.

No MeSH data available.


Related in: MedlinePlus

Comparison between (a) the real Instrumental Intensity (IMM) distribution and the predicted Pd distribution that would have been available (b) 20, (c) 30, (d) 40, (e) 50, and (f) 60 s after the OT.The Instrumental Intensity distribution (Figure 6a) has been performed by USGS41 and is downloaded from its website (http://earthquake.usgs.gov/earthquakes/shakemap/global/shake/2008ryan/). Figures 6b-6f show the distribution of Pd values, obtained after interpolating measured and predicted initial displacement values. The color transition from light blue to red represent the Pd = 0.2 cm isoline, which corresponds to a IMM = 7, based on the scaling relationship of equation (1) in Zollo et al.30. The available stations at each time are plotted with red and light blue triangles, based on the local alert level. The blue star represents the epicentre of the 2008 MW 7.9 Wenchuan earthquake. This figure is drawn using GMT software49.
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f6: Comparison between (a) the real Instrumental Intensity (IMM) distribution and the predicted Pd distribution that would have been available (b) 20, (c) 30, (d) 40, (e) 50, and (f) 60 s after the OT.The Instrumental Intensity distribution (Figure 6a) has been performed by USGS41 and is downloaded from its website (http://earthquake.usgs.gov/earthquakes/shakemap/global/shake/2008ryan/). Figures 6b-6f show the distribution of Pd values, obtained after interpolating measured and predicted initial displacement values. The color transition from light blue to red represent the Pd = 0.2 cm isoline, which corresponds to a IMM = 7, based on the scaling relationship of equation (1) in Zollo et al.30. The available stations at each time are plotted with red and light blue triangles, based on the local alert level. The blue star represents the epicentre of the 2008 MW 7.9 Wenchuan earthquake. This figure is drawn using GMT software49.

Mentions: Beyond the real-time magnitude estimation another relevant goal of an EEW system is the rapid identification of the Potentially Damaged Zone (PDZ) and prompt broadcasting of a warning in the highest vulnerable areas before the arrival of the strongest shaking, so that security actions can be rapidly activated (i.e., automatic shut down of pipeline and gas line, …). Following the same methodology as described in Colombelli et al.40, and using the empirical scaling relationship of Zollo et al.30 (equation 4), we estimated the Pd distribution for this earthquake, by interpolating the observed Pd values at close-in stations and the predicted Pd values at more distant sites. In Figure 6 we compare the Instrumental Intensity (IMM) distribution (Figure 6a) with the predicted Pd distribution that would have been available 20 (Figure 6b), 30 (Figure 6c), 40 (Figure 6d), 50 (Figure 6e) and 60 s (Figure 6f) after the OT. The Instrumental Intensity distribution (Figure 6a) has been obtained from the observed Peak Ground Velocity at all the available stations, using the conversion table of Wald et al.41. In Figures 6b–6f, the stations for which measured values of Pd and τc are available are plotted with red and light blue triangles; the color represents the local alert level that would have been assigned to each recording site, following the scheme proposed by Zollo et al.30. The alert levels can be interpreted in terms of potential damaging effects nearby the recording station and far away from it. For instance, an alert level 3 corresponds to an earthquake likely to have a large size and to be located close to the recording site, thus a high level of damage is expected both nearby and far away from the station. The PDZ of Figure 6b is fairly consistent with the area where the highest intensity values are observed (i.e., IMM > 7). Although the first reliable mapping of the Pd distribution is available 20 s after OT, the local alert levels at the stations are available well before (two alert level 3 at the closest stations are available 12 s after the OT); this information can be used to issue a warning, despite the magnitude estimation has not yet reached its final value. A stable Pd distribution is finally available later in time, around 40 s after OT (Figure 6d). However, in the north-east part of Sichuan province the intensity values are not well reproduced, probably due to the sparse distribution of strong-motion stations.


Early magnitude estimation for the MW7.9 Wenchuan earthquake using progressively expanded P-wave time window.

Peng C, Yang J, Zheng Y, Xu Z, Jiang X - Sci Rep (2014)

Comparison between (a) the real Instrumental Intensity (IMM) distribution and the predicted Pd distribution that would have been available (b) 20, (c) 30, (d) 40, (e) 50, and (f) 60 s after the OT.The Instrumental Intensity distribution (Figure 6a) has been performed by USGS41 and is downloaded from its website (http://earthquake.usgs.gov/earthquakes/shakemap/global/shake/2008ryan/). Figures 6b-6f show the distribution of Pd values, obtained after interpolating measured and predicted initial displacement values. The color transition from light blue to red represent the Pd = 0.2 cm isoline, which corresponds to a IMM = 7, based on the scaling relationship of equation (1) in Zollo et al.30. The available stations at each time are plotted with red and light blue triangles, based on the local alert level. The blue star represents the epicentre of the 2008 MW 7.9 Wenchuan earthquake. This figure is drawn using GMT software49.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4209451&req=5

f6: Comparison between (a) the real Instrumental Intensity (IMM) distribution and the predicted Pd distribution that would have been available (b) 20, (c) 30, (d) 40, (e) 50, and (f) 60 s after the OT.The Instrumental Intensity distribution (Figure 6a) has been performed by USGS41 and is downloaded from its website (http://earthquake.usgs.gov/earthquakes/shakemap/global/shake/2008ryan/). Figures 6b-6f show the distribution of Pd values, obtained after interpolating measured and predicted initial displacement values. The color transition from light blue to red represent the Pd = 0.2 cm isoline, which corresponds to a IMM = 7, based on the scaling relationship of equation (1) in Zollo et al.30. The available stations at each time are plotted with red and light blue triangles, based on the local alert level. The blue star represents the epicentre of the 2008 MW 7.9 Wenchuan earthquake. This figure is drawn using GMT software49.
Mentions: Beyond the real-time magnitude estimation another relevant goal of an EEW system is the rapid identification of the Potentially Damaged Zone (PDZ) and prompt broadcasting of a warning in the highest vulnerable areas before the arrival of the strongest shaking, so that security actions can be rapidly activated (i.e., automatic shut down of pipeline and gas line, …). Following the same methodology as described in Colombelli et al.40, and using the empirical scaling relationship of Zollo et al.30 (equation 4), we estimated the Pd distribution for this earthquake, by interpolating the observed Pd values at close-in stations and the predicted Pd values at more distant sites. In Figure 6 we compare the Instrumental Intensity (IMM) distribution (Figure 6a) with the predicted Pd distribution that would have been available 20 (Figure 6b), 30 (Figure 6c), 40 (Figure 6d), 50 (Figure 6e) and 60 s (Figure 6f) after the OT. The Instrumental Intensity distribution (Figure 6a) has been obtained from the observed Peak Ground Velocity at all the available stations, using the conversion table of Wald et al.41. In Figures 6b–6f, the stations for which measured values of Pd and τc are available are plotted with red and light blue triangles; the color represents the local alert level that would have been assigned to each recording site, following the scheme proposed by Zollo et al.30. The alert levels can be interpreted in terms of potential damaging effects nearby the recording station and far away from it. For instance, an alert level 3 corresponds to an earthquake likely to have a large size and to be located close to the recording site, thus a high level of damage is expected both nearby and far away from the station. The PDZ of Figure 6b is fairly consistent with the area where the highest intensity values are observed (i.e., IMM > 7). Although the first reliable mapping of the Pd distribution is available 20 s after OT, the local alert levels at the stations are available well before (two alert level 3 at the closest stations are available 12 s after the OT); this information can be used to issue a warning, despite the magnitude estimation has not yet reached its final value. A stable Pd distribution is finally available later in time, around 40 s after OT (Figure 6d). However, in the north-east part of Sichuan province the intensity values are not well reproduced, probably due to the sparse distribution of strong-motion stations.

Bottom Line: This information would have been available 40 s after the earthquake origin time and could have been refined in the successive 20 s using data from more distant stations.The reason for the magnitude underestimation is in part a combined effect of high-pass filtering and frequency dependence of the main radiating source during the rupture process.Finally we suggest only using Pd alone for magnitude estimation because of its slight magnitude saturation compared to the τc magnitude.

View Article: PubMed Central - PubMed

Affiliation: Institute of Geophysics, China Earthquake Administration, No. 5 Minzudaxue South Road, Haidian District, Beijing 100081, China.

ABSTRACT
More and more earthquake early warning systems (EEWS) are developed or currently being tested in many active seismic regions of the world. A well-known problem with real-time procedures is the parameter saturation, which may lead to magnitude underestimation for large earthquakes. In this paper, the method used to the MW9.0 Tohoku-Oki earthquake is explored with strong-motion records of the MW7.9, 2008 Wenchuan earthquake. We measure two early warning parameters by progressively expanding the P-wave time window (PTW) and distance range, to provide early magnitude estimates and a rapid prediction of the potential damage area. This information would have been available 40 s after the earthquake origin time and could have been refined in the successive 20 s using data from more distant stations. We show the suitability of the existing regression relationships between early warning parameters and magnitude, provided that an appropriate PTW is used for parameter estimation. The reason for the magnitude underestimation is in part a combined effect of high-pass filtering and frequency dependence of the main radiating source during the rupture process. Finally we suggest only using Pd alone for magnitude estimation because of its slight magnitude saturation compared to the τc magnitude.

No MeSH data available.


Related in: MedlinePlus