Cali. Quake

[Ubersheist]

Someone asked whether Mt. St. Helens and the earthquake could be related. Absolutely. I'm sort of an amateur geologist, have been studying the stuff for decades....I've concluded that periods of high precipitation followed by great heat (that's September in the Central Valley for you!) seem to cause more earth movement.
Julie

Um.... as a working geologist, I can aver that the two incidents have nothing to do with each other. The seismic forces at work for this recent 5.9 quake has nothing to do with the volcanic seismic forces at Mt. St. Helens. They're too different mechanisms created by two entirely different tectonic situations.

In addition, the theory that earthquakes are more frequent after periods of high precipitation is shakey (pun intended) at best and ONLY relates to seismic activity from a tectonic source, not from volcanism. While there is some physical and theorhetical evidence to support this line of thought, the general consensous amoung geologists is that the increased likelyhood is very slight at best. There is no evidence that I know of that indicates that volcanic activity or related seismic activity is influenced to a measureable or percievable amount due to climactic fluxuations. It's not my forte as a geologist, so there may be some recent studies in the last few years that say differently, but I highly doubt it. Are there any?

[Skidancer]

Damn, now I have to go look for my sources of information. I can't remember if it was in Scientific America or...... Anyway, I thought earthquake prediction was a VERY inexact science. I remember all the debate in the 70's: do frequent small earthquakes lead to bigger, subsequent ones or do they relieve pressure? I've had a number of colleagues look at data on rain, volcanic activity and earthquakes. There seems to be a connection, but we may never be able to actually quantify it.

I wasn't trying to step on anyone's toes or question your expertise, just throwing out some fodder for thought. What are some correlations with earthquakes and anything else??????

Say what you want, I never jumped too high while living in SoCal (LOL)

[Ubersheist]

What are some correlations with earthquakes and anything else??????

Earthquakes correlate to the ground shaking and, if it's a big one, subsequent interviews conducted by television reporters with the biggest, dumbest, shirtless oafs or house-fraus (usually with thier hair up in curlers even if it's 3:00 in the afternoon) in thier dundies that they can find!

No toes were stepped on. I just wanted to set the record straight as I saw it!

Our understanding of tectonic earthquakes (the ones resulting from shifts in the plates, etc) is terrible. It's a part of the science that's still in it's infantile stages. We know general areas where tectonic earthquakes occur, and that's about it. Forget about trying to predict where, when or to what intensity. The only true correlations that earthquakes have is that they almost all occur adjacent to plate boundaries or in areas of volcanic activity. There's a few other places that they occur, but they're fairly rare.

Also, someone mentioned that they're expecting "The Big One" sometime on the San Andreas Fault. This is only sort of true.

The pseudo-prediction says that "The Big One" will likely happen somewhere near Cajon Pass or San Bernardino, which is many hundreds of miles away from where this latest quake occured. In addition, the "Big One" scenario is based on a slip-rate for the San Andreas that came about from a paper written by a geologist named Kerry Sieh back in the early '80s on offset peats in a prehistoric bog north of Los Angeles. While it's a well written paper, many geologists have been questioning it's relativity to the rest of the San Andreas Fault. In predicting the location of "The Big One," a whole lot of other data is used, as well as a whole lot of assumptions. As such, most geologists (especially ones studying the Los Angeles Area) refute the credibility of the "Big One."

I, too, don't think the idea of the "Big One" holds much water. I'm not saying that I don't think it will happen, just that we don't have any idea if it will or not, or even where it will occur if it should occur. I certainly wouldn't avoid areas like Los Angeles or San Francisco because of earthquakes. My thought is that no matter where you live, there's always a threat of some sort of natural disaster.

[Ogre]

Earthquakes correlate to the ground shaking and, if it's a big one, subsequent interviews conducted by television reporters with the biggest, dumbest, shirtless oafs or house-fraus (usually with thier hair up in curlers even if it's 3:00 in the afternoon) in thier dundies that they can find!

No toes were stepped on. I just wanted to set the record straight as I saw it!

Our understanding of tectonic earthquakes (the ones resulting from shifts in the plates, etc) is terrible. It's a part of the science that's still in it's infantile stages. We know general areas where tectonic earthquakes occur, and that's about it. Forget about trying to predict where, when or to what intensity. The only true correlations that earthquakes have is that they almost all occur adjacent to plate boundaries or in areas of volcanic activity. There's a few other places that they occur, but they're fairly rare.

Also, someone mentioned that they're expecting "The Big One" sometime on the San Andreas Fault. This is only sort of true.

The pseudo-prediction says that "The Big One" will likely happen somewhere near Cajon Pass or San Bernardino, which is many hundreds of miles away from where this latest quake occured. In addition, the "Big One" scenario is based on a slip-rate for the San Andreas that came about from a paper written by a geologist named Kerry Sieh back in the early '80s on offset peats in a prehistoric bog north of Los Angeles. While it's a well written paper, many geologists have been questioning it's relativity to the rest of the San Andreas Fault. In predicting the location of "The Big One," a whole lot of other data is used, as well as a whole lot of assumptions. As such, most geologists (especially ones studying the Los Angeles Area) refute the credibility of the "Big One."

I, too, don't think the idea of the "Big One" holds much water. I'm not saying that I don't think it will happen, just that we don't have any idea if it will or not, or even where it will occur if it should occur. I certainly wouldn't avoid areas like Los Angeles or San Francisco because of earthquakes. My thought is that no matter where you live, there's always a threat of some sort of natural disaster.

GRRRRRRRRRRRRRR!!! You're starting to PISS ME OFF!!!!

[Skidancer]

Yep, Ubersheist (how do you umlaut?). Living for years in the Inland Empire, we would always observe a moment of silence as we passed over Cajon Pass (San Andreas/San Jacinto Faults). I'm familiar with the studies of which you speak and agree with most everything you say (especially correlations with dumbshit reporters, eyewitnesses, etc.

I'm getting all tingly knowing someone else interested in geology is on the boards. People usually stare at me dumbly and ask, "what's so interesting about a bunch of rocks?...." When I tell them I'm especially interested in Meteorology, they nod in a "She's crazy and weird but I'll humor her" sort of way.

Anyway, I enjoyed the discourse.

Hope things settle down in Cali so people have a chance to collect themselves and let everyone know how they're doing. Our attempts at "scientificizing" natural catastrophes is by no means an attempt to downplay our sympathies and concern.

Take care all

[ak_powder_monkey]

5.8s are pretty fun nice lttle jolt I've felt 7s they were pretty far away but long kinda freaked me out cause the '64 quake was a long about 7 and then it jolted like hell... Earthquakes are fun

[FollowMe]

... Earthquakes are fun

Yeah, i bet the poor fuck that didn't quite clear this gap thought it was fun...

http://wrgis.wr.usgs.gov/dds/dds-29/screens/016sr.jpeg

http://www.metroactive.com/urbanview...uide1-0237.jpg

I still remember dropping my jaw when I saw the home video footie of that lucky mother...

[Arty50]

That was just because NorCal engineers are morons.

Gee...let's build a very large bridge on top of wooden piling that will eventually rot. We are so SMRT!!!!

And don't get me started on the Nimitz freeway. That took over a decade and a half to rebuild. LA got up and running months after the Northridge quake.

The 5/14 interchange didn't fare so well either, so naturally I'm just joking.

As far as offering symapathies and stuff, it's appreciated. However, I'd say most earthquakes in the US are non-events. Sure the house shakes and you run into a doorjamb. Maybe a few glasses break too. But the devastation is generally nothing in comparison to the havoc hurricanes and tornados wreak on the rest of the country. After all, there's no such thing as a small hurricane.

Small earthquakes however comprise most of the events out here. Every couple of decades you have a larger one hit though, and it will cause some damage. But it's not like entire neighborhoods are leveled and whole cities are evacuated. In the last 28 years there have only really been 3 earthquakes of note damage wise: Whittier Narrows (5.9), Northridge (6.7), and Loma Prieta (6.9). This most recent quake occurred in a relatively unpopulated area. The three I mentioned above were all in major metropolitain areas. Now compare this to the number of hurricanes that hit Florida this year alone. I'll take earthquakes thank you very much.

Things don't start getting interesting until you hit around 6 and up. I've been in a couple of 5s and they weren't a big deal. In fact you can sleep through most of the smaller ones. Whittier scared the shit out of me, but it was also my first earthquake. I was on the opposite end of the state for the Northridge and Loma Prieta quakes luckily.

What people also forget to mention is that one's proximity to the quake is very important. I once met a seismology professor at CalTech and he explained that a "Big One" (say an 8.0 on the San Andreas) really wouldn't be that big of a deal. By the time it reached say Pasadena, it would feel similar to how the Whittier quake felt in the same city. Depending on who you talked to about the Northridge quake, it was either horrible or not that bad. The answer would always correlate with distance from the epicenter.

There is one more thing to add, there are different types of quakes also. I don't know the technical terms, but some are very jarring while others have more of a rolling motion. The rolling ones aren't so bad. They kinda shake you back and forth in a wavy motion. It's the jarring ones that fuck with your head. They're much more violent It's similar to being on a flight with really bad turbulence. They're really quick shocks that make you feel like your going to fly straight up out of your seat and hit your head.

[gravitylover]

It's not just the distance from the epicenter it's also the type of ground you're standing on, the depth of the shock and the wavelength the shock has generated.

[Skidancer]

Don't forget the San Fernando earthquake of '71 (a 6.6). It really messed a lot of things up (near LA). It's where the Valley girls used to jive.

P-waves cause alternating compressions and expansions (like smashing into the side of a tectonic plate with a really big truck). S-waves are shear waves that oscillate at right angles to their direction of motion and supposedly cannot travel well through liquids. P waves travel faster than Ss. Then there are surface (or L)waves which travell along the top of the crust that toss things in a way similar to what the ocean does to boats, etc. They also have a side to side component that causes the most damage to buildings and foundations.

[Ubersheist]

Sure the house shakes and you run into a doorjamb.

This is a dangerous misconceptions. Door jams tend to be attached to doors that get violent in big quakes. A hallway is a much safer place.

I once met a seismology professor at CalTech and he explained that a "Big One" (say an 8.0 on the San Andreas) really wouldn't be that big of a deal. By the time it reached say Pasadena, it would feel similar to how the Whittier quake felt in the same city. Depending on who you talked to about the Northridge quake, it was either horrible or not that bad. The answer would always correlate with distance from the epicenter.

This is only half true. Yes, it does matter how far away you are. However, a huge often overlooked factor is the geology that you're on at the time of the quake. If you're on top of a thick sequence of unconsolidated alluvial material, the ground acts sort of like a spring, making the shaking far more intense then if you were built on solid bedrock, like granite or sandstone. This is in part why some houses (probably built on man-made fill) in the Northridge quake crumbled, while the house next to it (with it's foundations firmly placed on natural soils or solid rock) withstood the shaking.

Also, if you did get an 8.0 in the Inland Empire, you'd get the shit scared out of you for sure in Pasadena. No question. That would be about the same distance from the Northridge Quake's epicenter as I was during that quake's shaking. It scared the daylights out of me. Mind you, the condo I was living in was probably built on fill...

There is one more thing to add, there are different types of quakes also. I don't know the technical terms, but some are very jarring while others have more of a rolling motion. The rolling ones aren't so bad. They kinda shake you back and forth in a wavy motion. It's the jarring ones that fuck with your head. They're much more violent It's similar to being on a flight with really bad turbulence. They're really quick shocks that make you feel like your going to fly straight up out of your seat and hit your head.

Actually, there's two types of earthquakes - tectonic (which we're talking about here) and ones related to volcanic (obviously not what we're talking about here). Niether one has a "rolling" effect greater then the other.

The "rolling" effect has to do with the fact that there's three sorts of seismic waves eminating from any earthquake's epicenter. First you get Primary Waves (or P-waves). These physically travel faster then the other types of waves and shake the ground back and forth without much up and down movement. The second fastest type of seismic wave (and the second to hit you) is uncreatively called Secondary Waves (or S-waves). These give you the horizontal shaking or "rolling" feeling. The third type is a wave whose name I can't remember - it's named after some dead scientist's name. They shake side to side. They're generally not as strong as the two other seismic wave types.

If you feel a rolling sensation, you're probably a good distance away from the epicenter. P-waves dissapate faster then S-waves because P-waves can travel through the liquid mantle of the planet. S-waves must remain in the crust, as they get reflected back as soon as they hit the crust/mantle contact and maintain more of thier energy over a distance. As such, 30 miles or so away from an epicenter will have more of a "rolling" feeling then a back and forth or side to side feeling. With that sort of distance, the earthquake has had enough area to disipate over. Therefore, the "rolling" wouldn't seem quite as bad as your "jarring" quake.

Hope that clears stuff up!

[The AD]

In the last 28 years there have only really been 3 earthquakes of note damage wise: Whittier Narrows (5.9), Northridge (6.7), and Loma Prieta (6.9).

Hey, don't leave us in the PNW out. The Nisqually quake on Feb. 28, 2001 was pretty good (6.8). It caused a fair amount of damage in Seattle and elsewhere.

[gageyk]

Fault types are also a factor in the type of earthquake. The Northridge earthquake was on a reverse or normal fault, I can remember exactly but the motion is similar. The San Andreas and most off-shoot faults are strike-slip.

Reverse and Normal faults have an up and down slip characteristic, think mountain building. Strike/Slip slide next to each other, the reason LA & SF will be suburbs of each other one day.

The Northridge quake was on a previously unknown Reverse fault. In my opinion the reason there was more widespread and severe damage with this quake was that most of the earthquake engineering in So Cal is designed for strike/slip motion.

I was in the 6.6 Sylmar quake of 1971, living in Northridge ironicaly enough. I was 9 years old. I can recount every second (61 of them) as if it happened yesterday. Our house slipped forward 2 inches, the driveway buckled, the chimney fell, all brick fences in the neighbor collapsed, the curb seperated from the street 2 inches. We had no power for 2-3 days and no water for 8 days. People often say a 6.6 isn't that big but from my experience it was huge and was the impetus for me to get my degree in Geology.

A thought to ponder for the other geo nerds. Is there a link between the increased activity in the Long Valley Caldera(Mammoth area) a couple of weeks a go and Mt St. Helens reawakening? Huge magma river?

[Ubersheist]

Fault types are also a factor in the type of earthquake. The Northridge earthquake was on a reverse or normal fault, I can remember exactly but the motion is similar. The San Andreas and most off-shoot faults are strike-slip.

The fault type has no bearing on an "earthquake type." Remember, there are essentially only two types of earthquakes:

• Tectonic, most commonly due to movement along any type of fault
• Volcanic - which is related to the movement of magma underneath the ground.

The only discernable differences in the seismic waves (earthquakes) produced by different fault types only is apparent in data from sensitive measuring equiptment (seismographs and other equiptment). There's no discernable damages, experiences or differences between a 6.0 from a thrust fault or a 6.0 from a strike/slip fault.

Reverse and Normal faults have an up and down slip characteristic, think mountain building. Strike/Slip slide next to each other, the reason LA & SF will be suburbs of each other one day.

This may be true about 10 million years from now or more. Here's an interesting thought:

There's a strong contingency of geologists that think the plate boundary between the Pacific and North American Plates will jump from the current San Andreas Fault, and create a new fault from the Salton Sea area up to the Owens Valley Fault area, and then northwards, possibly up to Reno, and cutting back somewhere that's undefined and unknown at this time. With this scenario, Mammoth may become a suburb of Reno in a few million years. However, the mountain will surely blow up by then, so the point will be moot!

The Northridge quake was on a previously unknown Reverse fault. In my opinion the reason there was more widespread and severe damage with this quake was that most of the earthquake engineering in So Cal is designed for strike/slip motion.

The Northridge quake was located on a "blind thrust fault." These are relatively newly discovered phenomena that has only been recognized in the last 10 to 15 years. Essentially, it's an active fault that's been buried with sediment, and therefore has no evidence of it's existance at the surface. They're extremely hard to find. You are right, though... No one knew about the blind thrust fault that produced the Northridge Quake.

Most of the damage occurred on buildings that were either relatively old and were built when certain modern building practices were not used, or on newer buildings that used poor building practices (i.e. the contractors got away with putting in substandard rebar in the footings, interiors were not built to code, etc.)

I was in the 6.6 Sylmar quake of 1971, living in Northridge ironicaly enough. I was 9 years old. I can recount every second (61 of them) as if it happened yesterday. Our house slipped forward 2 inches, the driveway buckled, the chimney fell, all brick fences in the neighbor collapsed, the curb seperated from the street 2 inches. We had no power for 2-3 days and no water for 8 days. People often say a 6.6 isn't that big but from my experience it was huge and was the impetus for me to get my degree in Geology.

A 6.6 is PLENTY big. I'll bet your draws were brown after that episode.

A thought to ponder for the other geo nerds. Is there a link between the increased activity in the Long Valley Caldera(Mammoth area) a couple of weeks a go and Mt St. Helens reawakening? Huge magma river?

Huge magma river? Where'd that come from? Convection cells?

The volcanic activity at Mammoth is essentially entirely unrelated to the volcanism at Mt. St. Helens. If you have been recently working in geology, you should know this. Remember volcanism as it relates to subduction zones versus hot spots? Mammoth is on top of a hot spot of sorts. Mt. St. Helens is a result of the small Juan De Fuca Plate (a small relic tectonic plate of the former Farallon Plate wedged in between the Pacific Plate and the North American Plate) being subducted under the North American Plate. The two have extremely little to do with each other.


Man - I do like rocks! My boss would be PISSED to see me writing all this crap on the board instead of making him money!

[CS]

We just got another one.

A bit softer than yesterdays, but longer.

[Arty50]

Ok, so I just got the smack laid down on me. But the bottom line is this, it takes a fairly large quake to wake me up and an even bigger one to get me out of bed. So in essence, I'm creating a new scale. The Arty Scale. So the next time there's a quake, NBC should call me. If I woke up, it's worth reporting. If I ran out of bed, they should cancel all other stories and go exclusive.

As for the Sylmar quake, I wasn't born yet. So that doesn't make the Arty Scale. Same goes for the Seattle quake. Those coffee drinking yuppies needed a wakeup call. (Is there a limit on smilies?)

[Skidancer]

I've never gotten a good answer to this question: when is it an aftershock? When we have 6ers and then feel little 1ers and 2ers afterwards, the latter are obviously considered aftershocks (the plates settling into position again or .....). What about this rash of 4ers and 5ers following the 6.0? I didn't have access to the internet way back in the days of college (eons ago!), but it seems that these are a lot of very large aftershocks coming on the tail of a fairly robust earthquake.

I'm seeing a lot of 3-5s all along the San Andreas and a few other areas where I can't find a known fault. Baja is having some activity as well. Just wondered what anyone knows about this. It just doesn't look good to me. Did they finally get everyone to jump off a chair at noon central time?

[tuffy109]

got my first wake-up quake last night.

[Ubersheist]

Aftershocks are a result of the fault settling in to it's new position. I could go on and on in detail about this, but I have a TPS report to produce by the end of the day. Here's how I'd put it in layman's terms:

When the main earthquake occurs (and the rocks along a fault physically shift in order to relieve built up stress or tension), it's never a perfect fit or position for the rocks. As such, they adjust (or have aftershocks) to better fit into thier new position. Sometimes these adjustments are nearly as great as the original move (or main earthquake), or they're relatively small.

In addition, there are usually aftershocks and smaller earthquakes on nearby faults, since the tension or stress has changed. In extremely rare cases, they can cause an even larger quake then the original quake (either on the same fault or on a nearby fault).

[Truckee Joe]

MAP 5.0 2004/09/30 11:54:28 35.984N 120.550W 10.1 14 km ( 9 mi) NW of Parkfield, CA
MAP 3.5 2004/09/29 22:02:27 35.953N 120.506W 9.7 9 km ( 6 mi) NW of Parkfield, CA
MAP 5.0 2004/09/29 15:54:54 35.389N 118.621W 5.6 17 km (11 mi) NNW of Keene, CA
MAP 4.5 2004/09/29 10:12:06 35.952N 120.492W 10.2 8 km ( 5 mi) NW of Parkfield, CA
MAP 5.0 2004/09/29 10:10:04 35.953N 120.502W 11.5 9 km ( 5 mi) NW of Parkfield, CA
MAP 3.1 2004/09/29 09:11:51 36.139N 120.207W 7.8 12 km ( 7 mi) SW of Huron, CA
MAP 3.2 2004/09/29 02:04:07 36.644N 120.880W 0.0 27 km (17 mi) ENE of Pinnacles, CA
MAP 3.3 2004/09/28 23:27:19 37.971N 118.661W 7.1 39 km (24 mi) SSW of Qualeys Camp, NV
MAP 3.4 2004/09/28 18:53:35 35.893N 120.446W 5.8 1 km ( 1 mi) WSW of Parkfield, CA
MAP 3.0 2004/09/28 12:59:27 35.903N 120.449W 6.2 2 km ( 1 mi) W of Parkfield, CA
MAP 4.0 2004/09/28 12:31:27 35.839N 120.387W 9.3 8 km ( 5 mi) SSE of Parkfield, CA
MAP 3.1 2004/09/28 12:23:39 35.830N 120.379W 6.6 9 km ( 6 mi) SSE of Parkfield, CA
MAP 3.6 2004/09/28 10:35:17 35.947N 120.489W 10.2 7 km ( 5 mi) NW of Parkfield, CA
MAP 3.7 2004/09/28 10:33:55 35.817N 120.359W 7.1 11 km ( 7 mi) SE of Parkfield, CA
MAP 3.2 2004/09/28 10:29:41 35.829N 120.369W 9.4 10 km ( 6 mi) SE of Parkfield, CA
MAP 3.3 2004/09/28 10:29:22 35.836N 120.380W 9.0 8 km ( 5 mi) SSE of Parkfield, CA
MAP 3.4 2004/09/28 10:29:15 35.852N 120.401W 5.3 6 km ( 4 mi) SSE of Parkfield, CA
MAP 4.7 2004/09/28 10:24:15 35.806N 120.349W 6.7 13 km ( 8 mi) SE of Parkfield, CA
MAP 3.0 2004/09/28 10:22:22 35.910N 120.458W 6.6 3 km ( 2 mi) WNW of Parkfield, CA
MAP 4.1 2004/09/28 10:22:18 35.840N 120.388W 5.6 8 km ( 5 mi) SSE of Parkfield, CA
MAP 5.0 2004/09/28 10:19:06 35.855N 120.411W 8.6 5 km ( 3 mi) SSE of Parkfield, CA
MAP 6.0 2004/09/28 10:15:24 35.815N 120.374W 7.9 11 km ( 7 mi) SSE of Parkfield, CA
MAP 3.4 2004/09/26 19:00:06 36.160N 120.662W 5.5 27 km (17 mi) NE of San Ardo, CA
MAP 3.7 2004/09/26 08:54:05 36.155N 120.654W 5.0 27 km (17 mi) W of Coalinga, CA
MAP 3.1 2004/09/24 10:27:03 38.014N 118.673W 10.6 35 km (22 mi) SSW of Qualeys Camp, NV
MAP 3.2 2004/09/23 17:07:03 37.993N 118.702W 4.9 36 km (23 mi) SE of Bodie, CA