If you could combine this preccursor with the EM studies
I have seen around San Francisco You might have a 1,2
combination for foreshadowing coming events.


On 3/25/2012 1:04 PM, Brett Nordgren wrote:
> Geoff and Wayne,
>
> The filter artifacts you describe sound like what you get from
> non-causal digital filtering. Non-causal just means that the usual
> relationship that effects can only occur after their causes, is
> violated; that is, that some change in the filter output can precede the
> input that "caused" it. I have seen data published before, suggesting
> that someone was seeing earthquake precursors which I believe were
> almost certainly the result of using some type of non-causal (IIR)
> digital filter. Although such types of filters have certain advantages,
> they probably shouldn't be used when seeking precursors.
>
> Of course you can't really get causes coming before effects. These
> filters are being applied, a little after the fact, to recorded, data.
> The filtered output data for a point at, say, 3 seconds are in effect,
> computed from data points recorded both before and after 3 seconds, so
> the filter apears to have some knowledge of what is coming in the future.
>
> Though the kinds of time intervals the researcher seems to be talking
> about would appear to be greater than you'd expect to get from
> non-causal filtering.
>
> I'd want to see a great many more examples before I'd get too excited
> about this. Although he apparently saw this phenomenon before one or two
> quakes, how often does it occur with no quake following, and how often
> do quakes occur without seeing it?
>
> Brett
>
> At 06:22 AM 3/25/2012, you wrote:
>> On 3/24/2012 3:03 PM, Wayne wrote:
>>> BBC video segment on analyzing GPS signals as precursors to equakes.
>>>
>>>
>>> 
>> I just hope the GPS predictor curve is happening
>> on a system not filtering the incoming data signal.
>>
>> That predictor curve may be a filter artifact
>> and not what they think it to be.
>>
>> I have seen defective precursors to earthquakes
>> arrival times using filtered geophone signals.
>> The filtering does something to add a undulation
>> before the actual signal has arrived.
>> But it is only a second or so of time.
>> Unfiltered signals do not seem to show this.
>>
>> geoff
>
>
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