Surveying in Active Seismic Regions

[JFC1]

I recently moved to L.A. from back east a couple of months ago, and the earthquake today got me wondering. Since part of California is on a different tectonic plate than the rest of the country, and is constantly moving in reference to the other plate, how do you deal with the coordinates of permanent benchmarks if they're moving 2" per year? I can see where as long as you stay on one plate or the other, everything is relatively uniform. But, wouldn't GPS equipment give you the exact position, which would conflict with the recorded coordinates?

I haven't had to deal with surveying on a project out here, yet, so I'm just curious. Do they not establish permanent benchmarks since there really is no such thing?

 

[msquared48]

Sssssssssshhhhhhhhh... Don't tell the lawyers!

Mike McCann
MMC Engineering

 

[bimr]

Here is a summary from the blm:

http://www.blm.gov/pgdata/etc/media...adastral/docs.Par.6253.File.dat/landslide.pdf

This report does not provide any "earthshaking" (no pun intended) solutions or miraculous cures for problems to be dealt with when survey monuments are destroyed or displaced by landslides or earthquakes. The intent is to provide some guidelines to follow when confronted with a situation.
Landslides are basically just another type of dependent resurvey problem created by a specific act of nature. The problems presented vary only slightly from other situations created by other natural phenomena such as forest fires, floods, etc., that destroy large numbers of survey monuments. The land surveyor must execute a dependent resurvey based on the remaining evidences, reconstruct the previous surveys and remonument the "lost" corners. Earthquake shifts are a case of their own.

The Alaska Landslide Act and California's Cullen Act seem to
provide a means to resolve large scale problems in heavily populated areas. Whether they can be made
applicable in other States is open to question. But without some clear legislation by the individual State,
those existing Acts are applicable only in California and Alaska.

In the City of Anchorage an earthquake shift occurred, along with the Sudden Landslides and vertical
displacements. A large part of the city was displaced up to about 15 feet in a horizontal shift and twisting action. Yet most of the infrastructure; lot lines, buildings, etc., were basically intact. The problem was what were the legal ramifications? The American Land Title Association (ALTA) was not concerned since they insure title but not location on the ground. To help resolve the problem the Alaska
Legislature enacted the "Earthslide Relief Act" in 1966, Chapter 80 Article 10, Sec. 09.45.800-Sec. 09.45.880. That Act provides for the resurvey and replatting of areas affected by the displacement of land boundaries shifted by an earthquake or landslide (a copy may be found in the appendix). A large area in the city was resurveyed and replatted, called the "L" Street Replat. That replat is discussed in the appendix.

The Alaska Earthslide Relief Act appears to have prompted a similar statute enacted by the California Legislature in 1972, called the "Cullen Earthquake Act," Title 10, Chapter 3.6, Sec. 751.50. The Cullen Act is nearly identical to the Alaskan legislation and permits the resurvey and replatting of an affected area. The Sylmar earthquake on February 9, 1971, may have been the direct impetus of the Cullen Act.
Sylmar is a heavily populated area in the northern end of the San Fernando Valley. According to Glen Nave of the Los Angeles City Surveyor's Office, the Sylmar displacement was up to about five feet and 0 16' of angle. Nave stated that there are 2000 to 3000 survey plats on file replatting lands affected by the Sylmar earthquake.

It should be remembered that professional land surveyors, including (but not limited to) the Cadastral Surveyors employed by the Bureau of Land Management, are not clothed with judicial authority. While they do execute many original surveys of the Federal public domain, their primary function in the context of this report is in executing dependent resurveys of the original surveys performed many years ago. Once those original surveys were executed and approved, and lands patented based on them, they become fixed in position and unchangeable in accordance with Statute and Case Law. The primary
function of the land surveyor, when executing dependent resurveys, is that of a professional gatherer of
evidence, and presenting that evidence in a clear and understandable manner. The plat(s) and field notes
should not be interpretable by only another surveyor familiar with cryptic jargon that non-surveyors do
not understand. The research into the past surveys, monumentation, records, etc., must be thoroughly
complete. The search for evidences of past surveys and monuments on the ground must also be well founded and complete. While so-called "gut feelings" and "instinct" may play a role in recovering evidence, they are not evidence in and of themselves. Once the surveyor has completed all of his research and retracements, gathered all of evidence, executed his dependent resurvey, drawn the plat and written the field notes, he then can testify as an expert witness as to what he has found and voice his expert opinion on where particular survey lines are located on the ground. And after all that, some court may completely overrule him in a judicial proceeding Frustrating?? Yes it is, but that's the way the judicial system works in this country. The very best protection the surveyor has is to be absolutely thorough in his investigations, not do them with a preconceived goal or conclusion that he wants to prove. Keep an open mind and let the chips fall where they may. In a word, be unbiased. That is my best advice based on my 50 plus years of experience. Don't be a victim of the question: Why is it--there is never time to do it right, but always time to do it over??

 

[MiketheEngineer]

Someday you will be an island... NOW that is a problem

 

[GoldDredger]

I had a geology professor in college (in California) describe to us that one day, San Francisco will be a suburb of Los Angeles. Each is adjacent to the fault line, but on opposite sides. The two plates are moving transverse.

Interesting question though, I've been watching this post with interest.

 

[civilperson]

Buy Arizona land for future seashore use.