Earthquake ground shaking scenarios

One of the key steps in seismic hazard and risk assessment is to be able to estimate the expected ground motions and shaking intensity levels produced by significant earthquakes.

In practice, from little information about a given earthquake (location, magnitude, and fault mechanism), Empirical Ground Motion Prediction Equations (GMPE) are used to compute values of ground motions parameters of engineering interest, such as Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV) and elastic response spectra in acceleration. GMPEs are empirical relationships derived through regression analysis of earthquake recordings databases. Then, these ground motions can be translated into macroseismic intensity values by using Ground Motion Intensity Conversion Equations (GMICEs, Caprio, et al., 2015). Macroseismic intensity represents, on a qualitative and discrete scale, a complex function between human perception of shaking, effects on objects, and damage levels to buildings (Picture 1).

In Quantectum, these maps of peak ground motions and intensities are automatically generated a few minutes following the occurrence of worldwide earthquakes having a moment magnitude Mw  5.5 (Picture 2). Both cases of shallow crustal earthquakes (GMPEs of Campbell and Bozorgnia, 2014) and subduction earthquakes (GMPEs of Zhao et al, 2006) are considered. Derived products are also proposed, such as cities and population exposure maps (Pictures 3 and 4).

Based on the concept of “ShakeMap” (Wald et al 1999), originally developed by the US Geological Survey (USGS), these maps are useful tools to assess the extent and the severity of felt shaking by population and the distribution of damage produced by moderate to large seismic events.

To better anticipate and mitigate potential future earthquakes, ground shaking scenarios computed from Quantectum forecasts are also provided. They facilitate notification of shaking alerts at user-selected critical facilities and can be used by both public and private institutions for planification of emergency response and loss modelings.

^{Picture 1: From basic seismological information (1), flowchart of the generation of earthquake ground shaking maps in terms of (2) ground motions parameters and (3) macroseismic intensities}

^{Picture 2: Example of estimated macroseismic intensities from the April 14th, 2016 Mw6.2 earthquake that occurred in Japan}

^{Picture 3: Selected cities potentially exposed to earthquake shaking in terms of macroseismic intensities for the 2016 Mw6.2 Japanese event}

^{Picture 4: Estimation of population exposure to levels of macroseismic intensity for the 2016 Mw6.2 Japanese earthquake}

Sources:

1) Campbell, K. W. and Y. Bozorgnia (2014), NGA-West2 Ground Motion Model for the Average Horizontal Components of PGA, PGV and 5% Damped Linear Acceleration Response Spectra, Earthquake Spectra, 30 (3), pp. 1087-1115.

2) Caprio, M., Tarigan, B., Worden, C. B., Wiemer, S., and D. J. Wald (2015), Ground motion to intensity conversion equations (GMICEs): A global relationship and evaluation of regional dependency, Bulletin of the Seismological Society of America, 15 (3), pp. 1476-1490.

3) Wald, D. J., Quitoriano, V., Heaton, T. H., Kanamori, H., Scrivner, C. W., and C. B. Worden (1999), TriNet “ShakeMaps”: Rapid generation of peak ground motion and intensity maps for earthquakes in southern California, Earthquake Spectra, 15 (3), pp.537-556.

4) Zhao, J. X., Zhang, J., Asano, A., Ohno, Y., Oouchi, T., Takahashi, T., Ogawa, H., Irikura, K., Thio, H. K., Somerville, P. G., Fukushima, Y., and Y. Fukushima (2006), Attenuation Relations of Strong Ground Motion in Japan Using Site Classification Based on Predominant Period, Bulletin of the Seismological Society of America, 96 (3), pp. 898-913.