Source - Wells and Coppersmith (1994)
Variable | Input | Units | Notes |
---|---|---|---|
cm. | |||
cm. | |||
m/s | Enter a value of 655 for no site effect Equation comes from Darvasi and Agnon (2019) |
||
Variable | Output - not considering a Site Effect | Units | Notes |
unitless | Moment Magnitude for Avg. Displacement | ||
unitless | Moment Magnitude for Max. Displacement | ||
Variable | Output - Site Effect Removal | Units | Notes |
unitless | Reduce Intensity Estimate by this amount to get a pre-amplification value of Intensity |
The value given for Intensity with site effect removed is how much you should subtract from your Intensity estimate to obtain a pre-amplification value for Intensity. For example if the output is 0.5 and you estimated an Intensity of 8, your pre-amplification Intensity is now 7.5. An Intensity estimate with the site effect removed is helpful in producing an Intensity Map that will do a better job of "triangulating" the epicentral area. If you enter a VS30 greater than 655 m/s you will get a positive number, indicating that the site amplifies seismic energy. If you enter a VS30 less than 655 m/s you will get a negative number, indicating that the site attenuates seismic energy rather than amplifying it. Intensity Reduction (Ireduction) is calculated based on Equation 6 from Darvasi and Agnon (2019).
VS30 is the average seismic shear-wave velocity from the surface to a depth of 30 meters at earthquake frequencies (below ~5 Hz.). Darvasi and Agnon (2019) estimated VS30 for a number of sites in Israel. If you get VS30 from a well log, you will need to correct for intrinsic dispersion. There is a seperate geometric dispersion correction usually applied when processing the waveforms however geometric dispersion corrections are typically applied to a borehole Flexural mode generated from a Dipole source and for Dipole sources propagating in the first 30 meters of soft sediments, modal composition is typically dominated by the Stoneley wave. Shear from Stoneley estimates are approximate at best. This is a subject not well understood and widely ignored by the Geotechnical community and/or Civil Engineers but understood by a few specialists in borehole acoustics. Other considerations will apply if you get VS30 value from a cross well survey or a shallow seismic survey where the primary consideration is converting shear slowness from survey frequency to Earthquake frequency. There are also ways to estimate shear slowness from SPT & CPT tests.
Sand Blow | Sand Blow Thickness (m) | Thickness of Surface Layer (m) |
---|---|---|
SB1 | 0.5 | ? |
SB2 | 0.3 | ? |
Variable | Input | Units | Notes |
---|---|---|---|
g | Peak Horizontal Ground Acceleration | ||
Variable | Output (No Site Effect) |
Units | Notes |
unitless | Conversion from PGA to Intensity using Wald et al (1999) |
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