Liquefaction

[tq3610]

In the past when I've had potentially liquefiable soils I've evaluated liquefaction potential using the CRR:CSR method, which includes a magnitude scaling factor for the magnitude of earthquake in question. I'd refer to the USGS earthquake probability mapping program that mapped probability of the selected design quake magnitude to select the magnitude scaling factor.

As of a couple of years ago (or so) USGS did away with the magnitude probability mapper and replaced it with the PGA mapper. While PGA is part of the liquefaction analysis, I'm now left with no availability of magnitude information (other then referring to past maps I'd saved).

Has anyone else run into this issue with liquefaction analysis? Are you using a different evaluation method?

I live in the northeast, where typically the probability of a mag 5.5+ quake is low (less than 2% in most areas from the past mapper). So, I'd typically inform a client regarding risk of liquefaction and potential effect, but given the very low probability of a liquefaction-inducing quake, an owner will typically opt to accept the risk. However, as it stands now I'm a bit short handed on giving a complete disclosure of risk without the magnitude maps.

 

[GeoEnvGuy]

In Canada the seismic hazard maps only generate the PGA and spectral accelerations. You need to contact the seismic research council for the magnitude hazard for your project coordinates.

The method they use to generate the magnitude hazard is freely available which can be calculated with the tools they make available. You can contact the USGS to see if they have something similar.

 

[HaiKenny]

Have you tried running deagreation from USGS Unified Hazard Tools which would provide the magnitude based on mean or modal. It's engineer judgement or local practice that dictate standards.