Author Topic: Earthquake! (Read 2368 times)

Raoul76 · « **Reply #10 on:** August 10, 2012, 12:58:16 AM »

Lefebvre is the second-most common name in France after Dupont, I believe.

Raoul76 · « **Reply #11 on:** August 10, 2012, 01:03:34 AM »

If that comment gets a thumbs-down it's most likely from Tele :wink:

catherineofsiena · « **Reply #12 on:** August 10, 2012, 01:53:24 AM »

LOL

Back on the subject, I guess Lefebvre is the French version of Smith or Jones :-)

Neil Obstat · « **Reply #13 on:** August 10, 2012, 03:11:46 AM »

When you consider the big picture these two (actually five) quakes in Los Angeles
are no big deal, as it's pretty much everyday stuff worldwide:

USGS Earthquake Tracker for Monday and Tuesday PDT (GMT -7)

   MAG    UTC DATE-TIME
y/m/d h:m:s     LAT deg    LON deg    DEPTH km     Region

MAP    2.6     2012/08/08 23:27:16     38.833     -122.880    2.6     NORTHERN CALIFORNIA
MAP    5.3     2012/08/08 22:42:12     -55.779     -26.095    20.1     SOUTH SANDWICH ISLANDS REGION
>MAP    2.6     2012/08/08 19:22:13     33.903     -117.784    8.7     GREATER LOS ANGELES AREA, CALIFORNIA
MAP    4.9     2012/08/08 17:45:33     44.431     -128.639    10.0     OFF THE COAST OF OREGON
>MAP    2.8     2012/08/08 17:36:26     33.904     -117.781    9.1     GREATER LOS ANGELES AREA, CALIFORNIA
MAP    2.8     2012/08/08 16:59:25     52.685     -168.237    22.5     FOX ISLANDS, ALEUTIAN ISLANDS, ALASKA
>MAP    3.4     2012/08/08 16:51:04     33.901     -117.789    9.5     GREATER LOS ANGELES AREA, CALIFORNIA
>MAP    4.5     2012/08/08 16:33:22     33.904     -117.789    9.7     GREATER LOS ANGELES AREA, CALIFORNIA
MAP    4.7     2012/08/08 16:14:05     -6.287     146.612    104.8     EASTERN NEW GUINEA REG, PAPUA NEW GUINEA
MAP    5.6     2012/08/08 14:05:19     54.980     -161.222    55.5     ALASKA PENINSULA
MAP    4.9     2012/08/08 12:08:19     -15.987     177.852    9.5     FIJI
MAP    5.8     2012/08/08 10:57:44     -16.041     178.141    12.3     FIJI
MAP    4.7     2012/08/08 10:09:17     -54.975     -27.725    9.2     SOUTH SANDWICH ISLANDS REGION
MAP    3.8     2012/08/08 09:43:17     52.719     -169.647    1.8     FOX ISLANDS, ALEUTIAN ISLANDS, ALASKA
MAP    2.7     2012/08/08 09:12:38     62.376     -151.309    105.1     CENTRAL ALASKA
MAP    4.5     2012/08/08 09:00:45     -5.823     154.787    163.2     BOUGAINVILLE REGION, PAPUA NEW GUINEA
MAP    2.6     2012/08/08 08:50:45     40.128     -122.759    10.7     NORTHERN CALIFORNIA
MAP    4.5     2012/08/08 08:35:14     -9.593     -75.566    93.6     CENTRAL PERU
MAP    3.3     2012/08/08 07:44:06     19.620     -67.925    34.0     DOMINICAN REPUBLIC REGION
MAP    5.5     2012/08/08 07:11:03     25.882     125.037    135.0     SOUTHWESTERN RYUKYU ISLANDS, JAPAN
>MAP    4.5     2012/08/08 06:23:34     33.907     -117.790    10.4     GREATER LOS ANGELES AREA, CALIFORNIA
MAP    4.7     2012/08/08 05:57:21     48.118     146.378    486.3     SEA OF OKHOTSK
MAP    2.7     2012/08/08 02:56:56     41.160     -123.396    40.0     NORTHERN CALIFORNIA

Notice: there were 8 earthquakes in the same time period that were larger in
magnitude than the L.A. quakes.

Note: the correct term to use is "magnitude" not "on the Richter Scale" because
the Richter Scale is obsolete for larger quakes and is only used for very small
ones anymore. To make it simple, seismologists have abandoned its use, and
you'll only hear it from reporters out of ignorance or a desire to appeal to the
audience and therefore sell copy.

Neil Obstat · « **Reply #14 on:** August 10, 2012, 03:36:43 AM »

Seismologists would look at this data and notice first of all that these 5 quakes
occurred at approximately the same area on the surface, that is, at the respective
epicenters, but they were "moving" in a generally consistent direction.

The depth became increasingly shallow, first of all. The first quake was at 10.4 km,
and the second moved up to 9.7 km, the third to 9.5 km and followed by 9.1 and
8.7 respectively. Therefore, the 5 quakes, as they generally became less strong,
were originating at less depth, one after the other.

As for location, longitutde of 33.907 to 33.903 doesn't make for much difference -
about a few hundred feet north/south. And latitude of -117.790 to 117.781 isn't
much either, about a quarter mile, east/west. So they can all be said to have been
in the same locality without distinction.

The depth having been reduced and the magnitude coming down as well, would
have given the residents of the area the impression that the quakes were very
much the same, for a weaker quake at a shallower depth has the feeling of the
same sort of quake as a stronger one at greater depth, when you are standing
directly above them both, as those people at the epicenters were.

The second and third quakes would have seemed to be strong and weaker, but
the fourth and fifth quakes would have seemed the same as the third. So if you
ask a local, he would say there were 5 quakes, and they each got a little less
strong, but not much.