Surprise earthquake alert
By Denise
@petatonicsca (7070)
Japan
October 3, 2018 7:14pm CST
While America was "looking forward" to a test of their system, Tokyo got an emergency earthquake alert in the middle of the night. It woke most of us up, scared us out of any more sleep, and nothing happened.
The earthquake was a 4.6 off Chiba shore and very much like earthquakes that happen at least twice a week in the same location.
I don't know what happened, but I'm going to be sleepy today. Anyway, I'm glad that we do have an automated system that will warn us, even if it glitches occasionally.
Do you have any theories about why an automated system would send out an alert for a usual small earthquake?
12 people like this
12 responses
@petatonicsca (7070)
• Japan
5 Oct 18
Yes, true enough. The last alert I got that was not for an earthquake was for flooding along river banks (I'm not along the river) and that elderly and children should evacuate just in case. That was an alert from my city office at 11:45 p.m.
2 people like this
@petatonicsca (7070)
• Japan
5 Oct 18
We have an alert system that works well 98% of the time.
1 person likes this
@May2k8 (19788)
• Indonesia
4 Oct 18
@petatonicsca We in Indonesia do not yet have an alert system, maybe in Japan it just trial, so every time there is a disaster they will send you alert immediately.
@petatonicsca (7070)
• Japan
5 Oct 18
@May2k8 It is definitely not just trial, it's been operative since the late 1990s. Every once in a while it messes up but usually it functions quite well unless you are near an epicenter of a large quake, in which case you feel it and then get an alert.
1 person likes this
@LadyDuck (502148)
• Italy
5 Oct 18
@petatonicsca It's better to receive an alert and no shakes than not to be informed.
@petatonicsca (7070)
• Japan
5 Oct 18
I think it was a bug in the system. Last year we got an alert for a major quake that was triggered by two small quakes on opposite sides of the island happening at exactly the same time. One week later we had a real shake and fortunately the system worked well for that one (I had 20 seconds warning.)
2 people like this
@petatonicsca (7070)
• Japan
4 Oct 18
It's supposed to be seismic intensity (how hard it shakes) and not Richter. This was estimated at a 4. Usually a seismic intensity 5 for your area triggers it. I think this one got loose because it was a seismic intensity 0 or 1 in my area.
1 person likes this
@josie_ (10033)
• Philippines
4 Oct 18
@petatonicsca _It's a good thing nothing serious occur. I went through a harrowing experience in 1990 when a magnitude 7.7 earthquake hit our region in the Philippines.
@peavey (16936)
• United States
4 Oct 18
I don't know much about these systems or earthquakes either, for that matter, but if the alarm is computer controlled and supposed to be sensitive to certain input, things can go wrong.
I have a fire alarm that tends to go off at random times and I have yet to discover what causes it.
In other words, I don't know. 
@Hate2Iron (15724)
• Canada
4 Oct 18
That has to be pretty scary. I hope that all is well. Will be thinking about you for the rest of the evening!!
1 person likes this
@ridingbet (66854)
• Philippines
5 Oct 18
my son wanted to work there in japan but the visa of his friend was not approved. he ditched the idea and now he is a Philosophy teacher in the school where i am also employed. he teaches senior high school students.
one thing i told him that might have changed his mind on working there is that Japan is sometimes having earthquakes.
@petatonicsca (7070)
• Japan
5 Oct 18
I'm just counting it as a good drill. I did manage to get under my desk in less than 5 seconds from a sound sleep.
1 person likes this
@Starmaiden (9308)
• Canada
4 Oct 18
How would anyone know the magnitude of an earthquake before it happened?
I can understand why they'd give an alert, given the earthquake and tsunami in Indonesia about a week ago. Natural phenomena like earthquakes, hurricanes, tornadoes, typhoons and tsunamis are happening more often in these times, and they are expected to get worse. It's a good system to have during these times.
@petatonicsca (7070)
• Japan
5 Oct 18
It sends the alert when it happens. A sensor senses the P waves (first to arrive) and if they are large it estimates how large the magnitude will be. After the earthquake, the seismologists analyze all the data and come up with a final magnitude. Usually it is pretty close to what the automated sensors detected. In Japan the automated sensors are in the NIED High-Sensitivity system.
1 person likes this
