Earthquake Design Magnitude
Earthquake Design Magnitude
(OP)
What determines the magnitude of earthquake is used when coming up with earthquake loads? Obviously this varies with region, but is there a table that the design magnitude is pulled from or is there some chart that connects spectral acceleration to magnitudes? I'm trying to connect the values given on the USGS reports with something more widely understood such as "Magnitude 7" or something similar (not that the general public understands that much better, it just helps give some sort of frame of reference).






RE: Earthquake Design Magnitude
Dik
RE: Earthquake Design Magnitude
Here's a table of PGA and magnitude for California earthquakes:
The relationship between PGA (what the ground experiences) and Spectral Acceleration (what a building would experience) is established empirically (I believe ATC 3-06 does this?), but I think Sa tends to be around 1.5-2.5 PGA.
Brian C Potter, PE
Simple Supports - Back at it again with the engineering blog.
RE: Earthquake Design Magnitude
The accelerations used are based on observation, probabilities of occurring, etc.
As BP noted, there are a few empirical relations (that can satisfy a question from a client looking for a correlation).....but it's not 100% accurate.
RE: Earthquake Design Magnitude
RE: Earthquake Design Magnitude
As far as I know they are a statistical device with little mechanistic reasoning.
I wouldn't trust them for design (or anything) since they are typically expressed in log scale (where 1 is near the 10) and show high variability. We all know it's easy to lie with statistics.
Boore and Atkinson (2007) GMPE enjoy some popularity I believe.
RE: Earthquake Design Magnitude
RE: Earthquake Design Magnitude
What is the best answer to this question? We design based on asce/ibc code but neither of the code discuss the magnitude of earthquake.
RE: Earthquake Design Magnitude
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm
RE: Earthquake Design Magnitude
If you want to explain the significance of the earthquakes based on the acceleration values given on the different codes (i.e. IBC, ASCE 7-10), you could indicate that these values are for the "maximum considered earthquake" (MCE) for a specific area, which is an earthquake that is expected to occur once in approximately 2,500 years. I think that people will understand this as the "big one" regardless its "magnitude".
However, the actual design earthquake is a different history because it applies a factor (2/3) to the MCE which makes the accelerations to be equivalent to accelerations for a return period of 475 years (for some parts for the US).
I also agree with WARose: the registered PGA depends on site soil conditions. Also, the table from briancpotter is interesting. It correlates well with the assumed PGA for liquefaction analyses in Japan (0.35g) which is based on the 1995 Great Hanshin EQ (6.9 Mw).
RE: Earthquake Design Magnitude
https://earthquake.usgs.gov/learn/topics/mag_vs_in...