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Re: Mistreatment of Seismology Issues[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: Mistreatment of Seismology Issues
- From: Yank2002(--nospam--at)aol.com
- Date: Thu, 22 Oct 1998 11:57:15 EDT
To Ken Buzbee: Ken Buzbee wrote: <snip> >I would seem that there are at least 5 parameters that would help in >determining the damage that can be expected from an earthquake: >1) Richter magnitude >2) Duration >3) Frequency content >4) The characteristics of the structures being excited. >5) Accelerations <snip>Anyone care to add (or modify, or delete) from the above list? >It might be informative (for me, at least!) > I audited the first few weeks of a graduate level soil dynamics class recently at UCLA, and I would have to add to the list: 6) soil characteristics. The '85 (?) Mexico City earthquake was far from Mexico City, with relatively minor ground motions near Mexico City, yet the soil of that region amplified the accelerations tremendously--the professor referred to the effect as a bowl of jelly. Additionally, I must concur that Richter Magnitude alone does not tell the whole story by any means. The Modified Mercali Index was mentioned as a method of correlating earthquakes and damage, from MMI 1 (Not felt except by a very few under especially favorable circumstances) to MMI 12 (Damage total; practically all works of construction are damaged greatly or destroyed; waves seen on ground surface; lines of sight and level are distorted; objects thrown into the air). K. Buzbee, EIT. End of K. Buzbee post. ----------------------------------------------------------- My response: My original post was not meant to be a GEOLOGY 241(???) (seismology) lecture where I would want to explain the difference between Richter Scale Magnitude vs Moment Magnitude vs Modified Mercali Scale vs (and so on and on). .... It was addressed exclusively to the structural engineering audience as their concerns are very much different than those of geologist's. Also, my original post addresses seismic problems related ONLY to California "strike-slip" faults, not to earthquakes in Guam, Pacific Northwest, Chile or China where positions 2 through 5 as you define them are very much different and not even comparable to California quakes conditions. My original post questions the wisdom of denying the structural engineering practitioner the translation tools of Seismic Zone 4 design requirements to ANY acceptable magnitude scale values used by seismologists so that the structural engineer as well as his/her client know the name of the ball park their game will be played - so they can communicate better. One of the questions posted on the list-server was why Karen was so "touchy" about this issue as she reacted pretty strongly to someone's comments (opinions). My quess is that she went through an experience resembling a military conflict between two opposing parties and the aftereffects of the conflict were not very pleasant. The party which was not adequately prepared for the war (because it was misled by its inapt leaders as to the strength of its defenses) lost it. I was "there", also many of you, I am sure, so nothing further has to be said about it. For those who did not have a chance to read a summary of some of the government compiled statistics about (say) Northridge, here are some numbers: 57 dead 9300 injured $13 billion damage (the last number I saw was $22 billion) 50,000 homeless 13,000 buildings destroyed. This was the toll of an earthquake of ONLY 6.7 magnitude !!!!!!! Another message I have received says that "Pasadena has more to fear from the smaller but more numerous faults much closer". My comment: To begin with, Pasadena is about 32 to 40 miles away from the point(s) where the possibility of the San Andreas major energy release is expected by seismologists. Pasadena like any other community in California located on or near active seismic fault has to fear from less deadly but more frequent "lesser magnitude earthquakes". A minor fault (i.e other than San Andreas) in California historically produced an earthquake of less than 6.8 (using Richter scale magnitude). The San Andreas fault, historically, produced earthquakes up to 8.3 RS. When you project (interpolate) 8.3 earthquake (or any such number the San Andreas is able to generate) using very conservative linear shock dissipation at 32/40 mile distance from its epicenter, Pasadena will find out that the quake the city was exposed to was about 8.1. This seems to be much larger than 6.8 It translates to about 50 times more of total energy released by the San Andreas as opposed to "the local fault" total energy release - I did not use my calculator, but I think the ball park is in close neighborhood. There were other comments (via SEAINT and private) with regard to the "Mistreatment of Seismology Issues". I will respond to those soon. Thank you for your time.
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