Curious if anyone out there has any experience with fault lines? We are looking for a house in particular area of Houston and we know there is a fault line running through neighborhood. I obviously don't want a house directly over the line but I am curious if there is some rule of thumb as to how far away is far enough. Any help would be greatly appreciated.

I would not worry about any fault lines in the Houston area. Most of the lines are inactive. I can provide more information if you can specify what area of Houston you are talking about. I have done geologic work over the greater Houston area, and this has never been a concern. I would be more concerned with subsidence caused by oil extraction.

Thanks a lot. We are looking in the Memorial area just outside the beltway. Between Wilcrest and Kirkwood and between I10 and Memorial. Any info you have would be great. I found a study online done by a couple of UH grad students which helped.

Growing up in california, southern and northern, the distance from a fault line is not something to worry about. We had just moved into a new house that was roughly 100 miles from san francisco when the 1989 quake hit during the world series. It cracked our wall and our pool deck.

Long story short, you probably aren't going to pick a place in houston that is over 100 miles from a fault. If you are truly concerned about faults, get earthquake insurance that will be DIRT cheap in Houston.

Fault lines cause plenty of foundation problems in the Houston area. There's an older neighborhood just outside Beltway 8, north of Westheimer, with a fault line running right through it. Most of the homes have cracked slabs. Houston's a big enough place with such a large number of options that you shouldn't have to buy a house close to a fault line (the same stance I take on flood plain homes).

[This message has been edited by Buck Turgidson (edited 8/23/2009 8:01p).]

Sorry but some of you guys are dead wrong.

faulting remains a serious concern in the Houston Area. Yes many of the larger ones are currently not moving or have slowed down drastically but thats no guarantee of future behavior. That logic is like saying it's safe to build at the top of a volcanoe because it quit erupting last year. You're looking to buy a home that you'll own for years. That fault has been there for millions of years and will be there long after your home is gone.

What neighborhood are you looking in? My father used to work as a civil engineer and spent the last half of his career doing fault work in Houston, and I'm a geologist and have studied some of the Houston faults when I was in school.

edit to add, Cal... The danger in Houston is not earthquakes as the soil and bedrock (yes there is rock under houston it's just deep) does not store the stress required for a brittle failure. The faults do not move in earthquake producing stick/slip events rather by creeping.

Also, if the Houston Galveston Coastal Subsidence District is ever sunset by the TX Legislature you can guarantee that the City of Houston and others will return to greater use of groundwater since it's so much cheaper than surface water. Although there's data that shows the faults are not a barrier to the aquifers and drawdown is the same on both sides of the faults, their movement does seem to correlate to excesive pumping. At least when the pumping stopped they stopped or slowed. Faults in Montgomery County are still moving pretty good and pumping is ongoing & increasing there.

[This message has been edited by Kenneth_2003 (edited 8/24/2009 9:27a).]

Thanks for all the comments...

I am not worried about earthquakes more about the location of the fault line and how it may damage my foundation. I obviously don't want a house directly over the fault but was wondering how far I should try to get. Am I safe being next door?

The house we are looking at, the fault does not touch the property but runs reasonably close. I think it runs under the neighbors garage(all garages are detached and at rear of property).

Thoughts???

Walk every square inch of that property. And walk every accessable inch of the blocks around the property. Depending on the size of the fault (and I'm guessing this is a pretty good one) it'll be easy to see. You're looking for ridges or swales in yards, broken or even just cracked sidewalks. Broken or cracked or repaired streets. If you can track that sucker down on two blocks and through the neighbors place you should be able to get a good handle on exactly where it goes. They do not follow straight lines, but they aren't going to wiggle like a snake in 1 block either. Also keep in mind that sometimes these faults will lie "en echelon." One will die out, move over some distance and pick up again.

The thing that really distroys a house isn't the vertical movement along these faults. Of course the vertical movement doesn't do the house any good either. What really rips the house apart is the horizontal movement. The faults in the Houston area reach the surface at ~70* - 80* so there is a small horizontal component to the motion. If you're not on top of the fault some regional deformation can get you but it likely shouldn't be too bad. The down-thrown side of these faults tends to "roll over" into the fault rather than just sliding straight down. So because of this the land away from the fault will tilt gradually towards the fault scarp. Really though if the place is level now and movement remains low or non-existant you'll be fine.

I THINK when my father was doing detailed "fault hazard investigations" for clients he deliniated a "fault hazard band" across the fault. If the fault had a visible scarp the band was fairly narrow. If there was no visible scarp (not in your case) and he found it by drilling and logging borings across it then the band would be wider.

There's a chance I've seen the house you're looking at but I'll never know. Without doing a site visit I can't personally guarantee you'll be fine. If you really like the house it won't set you back too much $$ to hire a local qualified and liscensed geologist or civil engineer to take a look at it. I can recommend a few if you'd like.

Kenneth... Thanks... Recommendations would be great

I have tracked it throughout the neighborhood and feel very comfortable as to where it is. The house we are looking at is on the "highside".

If I understand you correctly, the more verticle the movement the less horizontal movement and visa versa???

We are going to have home inspected this week and I am going to call out some foundation folks to get their opinions as well.

Yes, as the "dip" (angle into the ground) gets steeper there is more vertical displacement and less horizontal displacement. There should also be less defformation on the high (or upthrown) side since it's the more stable side. The upthrown side isn't moving, rather the downthrown side is moving away. So if you're on the upthrown side you should be safer.

I'll get you a couple of names when I get home this evening.

1Aggie99... Contact Richard Howe with Terrain Solutions, Inc. They're in Houston

713-467-2900
rghowe @ terrainsolutionsinc . com

I know that he's done a lot of fault hazard mapping in that area as well as worked with the Subsidence District folks on various fault related projects. Dr. Carl Norman with UH (ret) is also a local expert on Houston's faulting and they've worked extensively together as well.

Best of luck!

Kenneth... Thanks a lot

I just sent him an email. I really appreciate everyones help

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There should also be less defformation on the high (or upthrown) side since it's the more stable side. The upthrown side isn't moving, rather the downthrown side is moving away. So if you're on the upthrown side you should be safer.

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This is assuming the fault is a hanging wall fault and not a strike-slip. Strike slip faults are subject to horizontal movements (ie: north south).

The reason I previously downplayed the fault location is based on my experience that most of the greater Houston area lies on clays and sands (some of them fluid sands). Unless your property lies in one of the subsiding regions near extraction sites, I would not be as concerned with fault zones as I would in the Hill Country (where bedrock can be at the surface). The flowing sands and substrate tends to be more forgiving than bedrock.

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Fault lines cause plenty of foundation problems in the Houston area. There's an older neighborhood just outside Beltway 8, north of Westheimer, with a fault line running right through it. Most of the homes have cracked slabs.

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I am interested in this and your attribution to the fault line as the cause of cracked slabs. In my experience, I have drilled up to 120 feet down and found only sands and clays. I detected more than 3 different water layers that could contribute towards subsidence. I do not have experience in this area deeper than 200 feet. Would you please tell me why you feel that the cracked slabs are fault based? I would like to know, as a geologist, why you feel this is so. I don't want to call anyone out on this thread, but I am always willing to learn. If you don't want to post your response, you can e-mail me at 99stefan@gmail.com.

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faulting remains a serious concern in the Houston Area.

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Where is this a concern outside the petroleum/water related subsidence zones? Contact me at my previously posted e-mail above if you do not wish to post on this forum.

Gahh!!! 20 min's typing up a reply/explanation and server error when I went to post. I'll retype it tonight 10thyr.

Dang! I hate it when that happens.

Sorry, got busy last night...

There is a significant body of evidence for these faults in the area. They have been extensively mapped. **Disclaimer... No one publishes a "fault hazard map" because not every location has been studied, and the level of detail on a map depends on the scale. Every investigation is unique based on the land owners or developers desire for the land. Each site needs to be individually investigated. End Disclaimer** Generally they fall into two broad categories:
Long Regional Faults -- These faults or system of faults can generally be traced over great distances and strike roughly parallel to the coast. Most of them are "down to the coast" so their hanging wall (side that's moving down) is on the coast side of the fault. Some of the larger fault systems have twin up to the coast faults associated with them. The up to the coast faults will be a short distance south of its partner. These faults have been extensively mapped in both the subsurface and the surface. If you look at some BW aerial photos around I-10 just W of Bltwy8 (pre development) you will see a break in ground color running east/west across the photo. THe soil on the down-thrown side of the fault stay's everso slightly moister so the grass was greener when the photo was taken. THis fault has also been mapped in the subsurface using shallow 100 -- 500 ft holes that were logged for electrical resistivity and natural gamma. This fault traveled through the parking lot of the old Igloo Plant. During the I-10 widening the lot was dug up and that area was turned into a detention pond. During the initail excavation, Richard Howe and Dr. Carl Norman (mentioned in an earlier post) mapped the fault in the open pit and wrote up a short article in the Houston Geological Society Bulliten. You can track the fault through BMC Softwares parking garage (it's being monitored regularly) and then to the SW into a neighborhood where you can easily map it through broken streets, sidewalks, lawns, and cracked houses. As a side note, the cracks in the houses are exceptionally sever because of the horizontal component of motion. So not only is one piece of the home is moving down, it's being moved away from the rest of the house.
These faults all dip steeply into the earth and then at depth (10,000 -- 20,000 feet) they flatten out and become horizontal. Their origin is unsure but likely falls into one of the following
1) They're associated with the original opening of the Gulf of Mexico during the early Jurassic. Motion along them would indicate that this part of the basin is growing and continuing to open.
2) They have been created due to the migration of the Louanne Salt. This salt is the first rocks deposited in the young GOM as the first water began to fill the basin, but wasn't flowing in fast enough to outpace evaporation. As you probably know, at high temp and pressure solid salt is extremely ductile and flows like a very viscous liquid. All geologists agree that teh Louanne is deffinately on the move.
3) These faults are the landward expression of an extremely large slope failure of the continental shelf into the Sygsbee Deep.

Local Faults --> These normal faults are shorter in nature. They are frequently associated with salt dome features and radiate outward from the dome. Ask the folks at Beckendorff Elementary School what happens when a wing of your brand new school is built across one of these faults that outcropps near the Tomball Salt Dome. In addition to inches of vertical displacement, when the building was surveyed it was noticeably LONGER than it was orignally constructed (this is not the approved method for adding sq footage to your home). Everything mentioned above about recogntion of them applies here as well.

Relation to subsidence & oil/gas --> In the wake of rampant and at the time unexplained subsidence during the 50's, 60's, and 70's the Harris-Galveston Coastal Subsidence District was created and given regulatroy authority by the Texas Legislature. They have conducted and continue to sponsor extensive research. With resepect to the salt dome faults it's easy to see how oil and gas exploration contributes to subsidence. In these cases the reservoirs are located only on 1 side of the fault since the fault itself is part of the trapping mechanism. Fortunately it's been observed that subsidence wanes as exploration moves deeper and deeper. This is because the deeper sands/shales are stroger and more well cemented than the shallower ones that more closely resemble an accumulation of loose sand. It's a more complicated question with water. The water wells that are used for municipal and industrial supply are on average 3,000' deep and pump from overpressured confined aquifers. Research has shown that the faults do not form barriers to aquifer flow. Never-the-less when the pumping was cut down or stopped, the subsidence stopped or slowed immediately. Whether or not this is a coincidence, it's not a bet I'm willing to take until additional research is conducted. This research is happening since the HGCSD is working closely with the local USGS to study the problem. Of interst is Montgomery county which is outside the regulatory authority of the HGCSD and the faults are continuing to move and all of those communities are using ground water. One of the worst examples of combined oil/gas exploration and groundwater use caused subsidence is the Brownwood Subdivision in Baytown. Drive over there and take a look some time. Hurricane Alecia (1983) did to that subdivision what Katrina did to NO. They had been sinking for years and had actually constructed a 3' levvee around the subdivision to keep the bay out at high tide. They'd been flooded before, but Alecia was the final coffin nail and the homes were all abandoned and demolished. It's now a nature preserve, and some of it's been used as artificial wetlands. Go by sometime and get out of the public areas it's wierd to see peoples slabs underwater. Interestingly just north of the subdivision is a very large rise in the land. As you drive north over that rise, you just drove over a fault scarp. This is one of the large regional faults. It crosses underneath the bay and some think it's the same one that cuts through the San Jacinto Battlegrounds (the Battlegrounds Fault).

It sounds like you're drilling water wells or monitor wells? When geologists and civil engineers are mapping thse faults they'll use holes the depth you said that you've drilled because the log correlation at those depths will show the faults. These shallow aquifers are not the ones that are contributing to either the fault motion or subsidence. They're simply not big enough. The deep aquifers have a high piezeometric pressure. (If you drill into the aquifer, say 3000', the water will rise and only have to be pumped from say 2000'). The system is in equilibrium with that additional pressure. IF you depressure the aquifer by over-pumping so the water will only rise say 500', a new equilibrium must be met with the weight of the overlying sand/clay. The result is collapsing pores within the aquifer whose space was once supported by water pressure. That is subsidence. We just still don't know why or how the faults are involed. The data shows that they are, we just don't know the why.

www.hgsubsidence.org

If you've got more questions let me know.

Edit to add: These continue to be important for several reasons. There are implications for existing construction, redevelopment, and new development. Structures and civil works that were built on these faults prior to their discovery must be at a minimum monitored, and frequently repair or modification is required. The elemenatary school I mentioned earlier lost a couple of classrooms when the building had to be cut in two and covered walkway built over the gap because the structural damage was so severe it threatened the integrity of the building. In cases of redevelopment the lessons learned by the original developer must be remembered by those working today. In 1958 Baytown built a new City Hall. A fault was known to be in the area (small local one) because of damage to local streets and a few homes. McClelland Engineers was hired and they identified where they thought it crossed the property and dug a series of 5 trenches across it. In every trench but the very last one they could clearly see the offset in some shallow soil layers and were able to accurately map teh fault across the property until it died out short of the last trench. The city buildings were built with an open courtyard on the fault. Years later a veterans group was granted permission to build a memorial fountain. Today the fountain is inopperable due to leaks caused by fault movement. The city apparently forgot why the buildings were separated and the fountain was built directly on top of the fault. Finally new developments must have their properties investigated to prevent loss. This is especially important if they are in an area where the faulting is known to occur. Even in areas where the faults are not currently moving, we don't know if or when they might move again. I'm not willing to take a gamble building a home, a business, a landfill, or any other critical infastructure on a fault because "it's not moving today." Ask BFI how they felt when they didn't do the full investigation and now they're opperating an extensive pump&treat and monitoring program in the watertable aquifers immediately down-dip of their landfill because a fault cut moved and cut their clay liner.

One last note... In the shallow soils the clean sands are cohesionless. There is no cementation between the grains to hold them together. Clays and silts do have cohesion and will move/fail based on their individual physical properties. Highly plastic clays in the near surface (~100' or so) can fail in a single plane and develop "slickensides." Other times they may fail in a more ductile manner and simply roll across the fault. There's a lot of variables in play that determine their response.

[This message has been edited by Kenneth_2003 (edited 8/27/2009 9:14a).]

Thanks for your reply Kenneth. I appreciate it greatly. I had neglected considering pressurized salts for some reason. As I stated before, most of my experience is with subsurface up to 200 feet. I had assumed that any fault movement in a region with flowing sands would be negated by the upward force of the pore pressure. I don't recall finding many flowing sands west of the beltway. Do you know of any fault information that occurs below flowing sands? The largest layer of flowing sands I have found is near the intersection of 59 and 610 (specifically at the intersection of Renwick and Gulfton), Do you have any fault data for this region? Thanks again for your post!

[This message has been edited by 10thYrSr (edited 8/28/2009 2:01a).]

*Disclaimer -- This is not to be considered engineering or geolocial consulting for anyone looking to build in this specific area*

Now that thats out of the way, no I do not know of any faults in the area around 59 & 610 or specifically the interesection you mentioned. That area is several miles south of the Long Point and Eureka Heights Fault System and there are no active salt domes in the Bellaire, Meyerland area.