[Duffy]

(10-30-2015, 09:43 PM)Skywise Wrote:

(10-28-2015, 09:23 PM)Duffy Wrote: Thanks for your responses guy's, appreciated ,,,,  Unfortunately,  I think the actual posting Its self may not have been intended for listing under "Significant Earthquakes......last 30 days", as I have recently checked the USGS 2015 archive and it isn't listed , I could be wrong but all the other quakes are there !!.

Many times events are updated as new information arrives and is analyzed. Sometimes when there is a larger quake somewhere the automated systems may get confused and put phantom quakes in odd places. Those get deleted later when a human looks at the data. Most quakes you see on the map, especially new ones, are automatically plotted by computers and the algorithms aren't perfect.

(10-28-2015, 09:23 PM)Duffy Wrote:   I'm sorry the question seemed irelevant  considering the magnitude, but I'd noted in resent weeks there had been a couple of 5.9's at 10 kms deep and wanted to understand how a 5.8 at 106 km deep could supersede them ! 

Location. Location. Location. A 5.9 under LA (or London!) would be very significant. A 5.9 out in the middle of the ocean doesn't get much attention other than being logged. Perhaps a better example magnitude might be a 4.0. In a place with good building codes like California or Japan, it gets noted in the local news but that's about it. In a 3rd world country where homes are made of mud brick, it can be devastating.

A note about depth. That "10km" you see is almost certainly a 'placeholder' depth. Depth is harder to determine than lat/lon, so the automatic solution may just use 10km as a temporary number unless it has enough data. And when more data arrives and is checked, the depth gets updated with a more accurate value.

Sometimes these updates can take a few days. The USGS folks do take the weekends and holidays off, and unless the quake is 'significant' it won't get checked until Monday. Sometimes they don't even show in the listings until then, or in the case of phantoms, get removed.

Brian

Amazing how much you take at face value, when your unaware of how the data is actually compiled. Thanks Brian, that's been really helpful.

Duffy,