earthquake

[songbird]

wow! first one i've been awake for.

songbird

[David E. Ross]

Where are you? What was the magnitude?

[songbird]

...

mid-Michigan, it was 4ish, down near Gaylesburg which is near Kalamazoo (SW side of the state). this area is fairly stable, so it's not something that happens often.

first one i've noticed, i know there have been a few smaller ones before that i wasn't sure i felt, but this one definitely shook the house for about 5 seconds. no damage...

not like the ones you get out there all the time.

songbird

[Frank]

Saw your post and saw it noted on internet:

Brother in law in Cleveland said he did not feel it or know anything about it.

I remember one here in Delaware over 40 years ago. I was woken up by what I thought was a big truck rumbling down the street. Found out the next day, it was an earthquake.

[songbird]

[Boron Elgar]

Family still there felt it.

Last time they had one this big was 1947. Damn near the same epicenter, too.

[David E. Ross]

In the past 24 hours, there were 12 earthquakes around the world with magnitudes greater than 4.2. Depending on the depth of the actual event and the local geology, however, 4.2 can be a very serious quake.

Living in southern California all my life, I recall 3 very significant earthquakes:

* On 21 July 1952 shortly before 4:00am local time, a 7.3 quake hit near Tehachapi in the Central Vally and killed 12 people. In Los Angeles, the shaking damaged a major electrical substation less than a mile from our house (about 115 miles from the epicenter). My mother said she saw the flashes as the transformers shorted. We were without electricity for several hours. Over a period of two months, 188 aftershocks had magnitudes of greater than 4.0. Property damage estimates were about $60,000,000. * On 9 February 1971 at about 6:00am, a 6.6 quake hit Sylmar in the north end of the city of Los Angeles and killed 65. My house (about 20 miles from the epicenter) suffered minor hairline cracks around windows. My son's bedroom was a mess because a large coffee can filled with crayons fell off his bookcase and spilled over his floor. We did not lose electricity, but water service was questionable because the dams for two major reservoirs within the city of Los Angeles began to fail. Two hospitals were destroyed, including one that tipped over. Parts of the freeway system collapsed. In the Angeles National Forest just north of Sylmar, the center stripe on a road was offset several feet. Property damage estimates were about $505,000,000.

Interestingly, this earthquake occurred very close to the time of a spectacular lunar eclipse. Not only were the sun, earth, and moon in a straight line; but also the moon in its elliptical orbit was at its closest point to the earth. Furthermore the earth was just a month from its closest to the sun. A geophysicist at the California Institute of Technology (CalTech) agreed with my speculation that this quake might have been triggered by the tidal stresses caused by the sun and moon. No, they did not cause the quake; but they might have been the trigger.

* On 17 January 1994 at about 4:30am, a 6.7 quake hit Northridge in the north-western end of the city of Los Angeles and killed 57. Repairs to the structure of my house (about 20 miles from the epicenter) cost over $70,000, and we had to move to an apartment while most of the repairs were underway. We were without electricity for most of a day. Freeways collapsed. Property damage estimates range from $13,000,000,000 to more than $20,000,000,000 (yes, billions of dollars) and nearly bankrupted several insurance companies that had issued insurance against earthquake damage.

Interestingly, all three quakes occurred at night, waking us from our sleep.

[David Hare-Scott]

[songbird]

David E. Ross wrote: ...

no damage reported other than a few broken windows or mirrors.

did they actually give way?

i was young enough that i don't recall this one, but the others i've some recall of them.

i would believe it. when you think about how the tidal forces can attract the water and how heavy water is that it surely does place some stresses on the earth.

another interesting tidbit of how things can go on the earth, there's so much ice in the south pole that it attracts the water from the surrounding oceans.

that would certainly be no fun, i'm glad you weren't injured.

i don't think i'd like that sort of wake up call...

songbird

[songbird]

David Hare-Scott wrote: ...

interesting, but perhaps your continent is fairly solid and stable? seems like i never hear of earthquakes in England either.

oops! those people from that area really had a rough time of it too (and still are as far as i'm concerned).

songbird

[David E. Ross]

On 5/3/2015 2:56 PM, songbird wrote [in part]:

I am not sure about the Pacoima reservoir because all of the attention was focused on the lower Van Norman reservoir. If the dam at the lower Van Norman reservoir had actually failed, a large part of the central San Fernando Valley of Los Angeles would have been destroyed, affecting an area of almost 1,000,000 residents. Both the upper and lower Van Norman reservoirs were quickly but carefully drained. A few years later, a smaller, single Van Norman reservoir was created with a dam that is more earthquake resistant.

My conjecture -- supported by the geophysicist (for whom I provided computer programming services at UCLA in the 1960s) -- was that the tidal stresses were not in the ocean but in the crust of the earth. A tidal bulge in the crust is known to exist. That bulge is raised by the moon's gravity. The bulge is increased when there is a solar or lunar eclipse, as the sun adds to the pull of the moon; it is also increased when the moon is closest to the earth and when the earth is closest to the sun, both the moon and earth having elliptical orbits.

The earth's rotation draws the bulge ahead of the earth-moon line, and it keeps moving back towards that line but not fast enough to reach it. The effect of this is causing a gradual slowing of the earth's rotation. It is also causing the moon to accelerate in its orbit around the earth and thus increasing the size of the moon's orbit, slowly moving the moon farther from the earth.

When I was a computer programmer at UCLA, some of the software I wrote modeled the effects the tidal bulge.

[songbird]

the past few months i've been going through various references/books about the development of the water sources out there and how that has gone. a few notable dam failures, can't say i'd want to be downhill from a large reservoir out there. even if designed to withstand an earthquake doesn't mean it actually will if a big enough one comes along. and if a really big one does come along, to have a dam failure on top of the damage already done... wowie... can't believe they haven't made a movie about this one yet...

in recent years i'm loving the river restoration efforts where they are starting to figure out that yes indeed those river flood plains have a real useful purpose besides being places to collect plastic bags.

yes, for sure. i should have been clearer in my comment in saying that if the tidal forces could move that much water then you know it's acting on the crust too even if it isn't so visible. with today's satellites they can probably follow it in realtime...

the other thing that changes it is the water impoundments... at least i recall someone writing an article about it a few years back.

:)

songbird

[David Hare-Scott]

Although on the coast not at the edge of a plate (which is at New Zealand) so i doubt anywhere in Oz has a building code for it.