SUBSIM Radio Room Forums - View Single Post - Southern California earthquakes of 6.4 on July 4th and 7.1 July 5th

vienna · 07-06-19, 02:53 PM

Here in Hollywood, we are about 150 miles away from the epicenters of the quakes from the past two days, but we definitely felt them, and some of the aftershocks. I'm originally from San Francisco and, in Northern CA, people are used to earthquakes; I usually don't give much attention to anything under a 5 on the Richter Scale. On the morning of July 4th, I was sitting down on an office chair in my home; I had minutes earlier nearly tipped over the chair with me on it when I had dropped something on the floor and awkwardly tried to lean over and pick it up; when the 6.4 hit, at first I thought the chair was slipping away again, but I immediately realized every thing else in the room was jerking about; the felling was not a hard jolt or jolts, but more like being in a small boat when a larger boat's wake hits it, a sort of shifting side to side and up and down motion; this went on for a good thirty seconds and I became a bit concerned about two-thirds of the way through we might be having a repeat of the Northridge earthquake of 1994. Interestingly, there was no sound of any kind, such as accompanies good-sized earthquakes. After it stopped, I knew whatever it was, it was a really strong quake and I turned on the TV to see if there were any reports about location, damage, etc. I flipped around the dial a few times and saw nothing other than the scheduled; apparently, the news personnel at the stations had ducked and covered at the time of the quake and it took sveral minutes for them to get it together. The magnitude was given as 6.4, the largest in SOCal in 20 years:

Early the next morning, July 5th, I woke up, for no reason, at a couple of minutes past 4:00 am; I lay there for a bit wondering why I was awake and trying to go back to sleep when the 5.4 aftershock hit, with the same 'bobbing boat' effect; that quake was about 15 seconds in length and, after briefly checking the TV news to see if there was anything to be concerned about, I went back to sleep...

Last night, I was in bed, watching TV, when the 7.1 quake hit; at first I thought it was another after shock, but it built up steam and really began to move, with the same 'bobbing boat' motion and lasting at least 30 seconds; almost immediately, the TV stations cut to news coverage and were in a better position to report since they still had news crews at the location(s) in the Ridgecrest epicenter area; some of the reporters on the scene, who had just moments before been at the center of the quake looked a bit apprehensive as they made their reports...

Ridgecrest is about 150 miles away fro LA, so for us to feel the quake that sharply give you an idea of how really powerful the quakes have been. The best news is that there have been no fatalities or major injuries and damage has been at a minimum considering the size of the quakes; the area is on the edge of the desert area in the East and is the home of the China Lake Naval Weapons Station, a major defense installation:

Naval Air Weapons Station China Lake --

https://en.wikipedia.org/wiki/Naval_...ion_China_Lake

The base is now closed due to the quakes, pending assessment:

Navy’s China Lake base closed, assessing damage after earthquakes --

https://www.stripes.com/news/us/navy...uakes-1.589148

Two factors of good fortune serving to minimize damage at the epicenter have been the fact the bedrock in the area is solid granite and able to endure shock with minimal fracturing and the fact most of the heavily populated areas are of recent development and the vast majority of the structures are low-rise and built to codes put in place after other devastating quakes in other ares of CA. If the same quakes had occurred in more densely populated areas with larger numbers of pre-code structures, the results would have been far less fortunate...

One of the things being talked about here in LA in the wake of the quakes has been a 'quake early-warning' system initiated in recent years and in early use via cellphone app(s). Basically, when sensors at the quake site detect a quake, a warning notification is sent to the app(s) alerting the users of possible ripple shocks headed their way; the amount of time of the warning varies by distance from the sensors; in LA, the time margin for the recent quakes was about 15 seconds. This may not sound like much, but there was a practical impromptu demonstration last night when, during a press conference at CalTech (Calif. Institute of Technology, 'home' to Sheldon Cooper) in Pasadena adjacent to LA,, a sensor alarm went off signalling an approximately 5.0 aftershock; the speaker noted the alarm and all assembled waited to see how long it took for the quake's shock to hit Pasadea; after 15 seconds the shock was felt; while watching this and waiting, 15 seconds was a surprisingly "long" time; I could have easily left my building and been outside away from any danger if I so chose; I may have to add that app to my cell (and I do hate to use apps)...

I have been through about a half-dozen major, damaging quakes since I came here to LA in 1970 and this is the first time in my life I have ever felt/seen a situation where what would be considered by accepted metrics as a major quake (6.4 magnitude) become 'demoted to a 'pre-shock' by a later quake (7.1 magnitude); it has always been major shock followed by diminishing after shocks; there are many, including myself, mulling over the possibility of yet larger shock to come and further 'demote' the current shocks...

@ mapuc: the Ridgecrest quakes are on 'small' faults in CA; the 'Big One' everyone is expecting and dreading would come from activity on the San Andreas Fault which is roughly 1,200 Km long and runs almost the entire length of CA:

San Andreas Fault --

https://en.wikipedia.org/wiki/San_Andreas_Fault

There have been past ruptures in areas of the fault, causing past major quakes, with the largest being The Great San Francisco Earthquake of 1906 which left 80% of the city in rubble and killed at least 3,000 people; there was a fire caused by effects of the Quake which consumed much of what was left of the city. We are still waiting for the 'Big One' on the San Andreas...

<O>

07-06-19, 02:53 PM	#6
vienna Navy Seal Join Date: Jun 2005 Location: Anywhere but the here & now... Posts: 7,506 Downloads: 85 Uploads: 0	Here in Hollywood, we are about 150 miles away from the epicenters of the quakes from the past two days, but we definitely felt them, and some of the aftershocks. I'm originally from San Francisco and, in Northern CA, people are used to earthquakes; I usually don't give much attention to anything under a 5 on the Richter Scale. On the morning of July 4th, I was sitting down on an office chair in my home; I had minutes earlier nearly tipped over the chair with me on it when I had dropped something on the floor and awkwardly tried to lean over and pick it up; when the 6.4 hit, at first I thought the chair was slipping away again, but I immediately realized every thing else in the room was jerking about; the felling was not a hard jolt or jolts, but more like being in a small boat when a larger boat's wake hits it, a sort of shifting side to side and up and down motion; this went on for a good thirty seconds and I became a bit concerned about two-thirds of the way through we might be having a repeat of the Northridge earthquake of 1994. Interestingly, there was no sound of any kind, such as accompanies good-sized earthquakes. After it stopped, I knew whatever it was, it was a really strong quake and I turned on the TV to see if there were any reports about location, damage, etc. I flipped around the dial a few times and saw nothing other than the scheduled; apparently, the news personnel at the stations had ducked and covered at the time of the quake and it took sveral minutes for them to get it together. The magnitude was given as 6.4, the largest in SOCal in 20 years: Early the next morning, July 5th, I woke up, for no reason, at a couple of minutes past 4:00 am; I lay there for a bit wondering why I was awake and trying to go back to sleep when the 5.4 aftershock hit, with the same 'bobbing boat' effect; that quake was about 15 seconds in length and, after briefly checking the TV news to see if there was anything to be concerned about, I went back to sleep... Last night, I was in bed, watching TV, when the 7.1 quake hit; at first I thought it was another after shock, but it built up steam and really began to move, with the same 'bobbing boat' motion and lasting at least 30 seconds; almost immediately, the TV stations cut to news coverage and were in a better position to report since they still had news crews at the location(s) in the Ridgecrest epicenter area; some of the reporters on the scene, who had just moments before been at the center of the quake looked a bit apprehensive as they made their reports... Ridgecrest is about 150 miles away fro LA, so for us to feel the quake that sharply give you an idea of how really powerful the quakes have been. The best news is that there have been no fatalities or major injuries and damage has been at a minimum considering the size of the quakes; the area is on the edge of the desert area in the East and is the home of the China Lake Naval Weapons Station, a major defense installation: Naval Air Weapons Station China Lake -- https://en.wikipedia.org/wiki/Naval_...ion_China_Lake The base is now closed due to the quakes, pending assessment: Navy’s China Lake base closed, assessing damage after earthquakes -- https://www.stripes.com/news/us/navy...uakes-1.589148 Two factors of good fortune serving to minimize damage at the epicenter have been the fact the bedrock in the area is solid granite and able to endure shock with minimal fracturing and the fact most of the heavily populated areas are of recent development and the vast majority of the structures are low-rise and built to codes put in place after other devastating quakes in other ares of CA. If the same quakes had occurred in more densely populated areas with larger numbers of pre-code structures, the results would have been far less fortunate... One of the things being talked about here in LA in the wake of the quakes has been a 'quake early-warning' system initiated in recent years and in early use via cellphone app(s). Basically, when sensors at the quake site detect a quake, a warning notification is sent to the app(s) alerting the users of possible ripple shocks headed their way; the amount of time of the warning varies by distance from the sensors; in LA, the time margin for the recent quakes was about 15 seconds. This may not sound like much, but there was a practical impromptu demonstration last night when, during a press conference at CalTech (Calif. Institute of Technology, 'home' to Sheldon Cooper) in Pasadena adjacent to LA,, a sensor alarm went off signalling an approximately 5.0 aftershock; the speaker noted the alarm and all assembled waited to see how long it took for the quake's shock to hit Pasadea; after 15 seconds the shock was felt; while watching this and waiting, 15 seconds was a surprisingly "long" time; I could have easily left my building and been outside away from any danger if I so chose; I may have to add that app to my cell (and I do hate to use apps)... I have been through about a half-dozen major, damaging quakes since I came here to LA in 1970 and this is the first time in my life I have ever felt/seen a situation where what would be considered by accepted metrics as a major quake (6.4 magnitude) become 'demoted to a 'pre-shock' by a later quake (7.1 magnitude); it has always been major shock followed by diminishing after shocks; there are many, including myself, mulling over the possibility of yet larger shock to come and further 'demote' the current shocks... @ mapuc: the Ridgecrest quakes are on 'small' faults in CA; the 'Big One' everyone is expecting and dreading would come from activity on the San Andreas Fault which is roughly 1,200 Km long and runs almost the entire length of CA: San Andreas Fault -- https://en.wikipedia.org/wiki/San_Andreas_Fault There have been past ruptures in areas of the fault, causing past major quakes, with the largest being The Great San Francisco Earthquake of 1906 which left 80% of the city in rubble and killed at least 3,000 people; there was a fire caused by effects of the Quake which consumed much of what was left of the city. We are still waiting for the 'Big One' on the San Andreas... <O> __________________ __________________________________________________ __ Last edited by vienna; 07-06-19 at 03:03 PM.