Friday, March 18, 2011

Aquifer Update and the Japan Earthquake connection

Drought Status: non-drought (but fast-approach Alarm Stage)
Barton Springs: 41 cfs (38 cfs 10-day average for Alarm Stage threshold)
Lovelady: 167.95 ft depth to water (175 ft is threshold for Alarm Stage)

The tragic earthquake in Japan on 3/11/11 was recorded in some water levels changes in the Edwards Aquifer. The Edwards Aquifer Authority (EAA) measured a water level change of about 1 foot related to the Japan Quake in their J17 drought index well. See chart below. A good summary as a audio clip is provided by the USGS here.

This information came from the EAA in the San Antonio segment of the Edwards Aquifer (courtesy of the EAA and Geary Schindel). People naturally asked if we saw something similar in the Barton Springs segment. The short answer is no, our instruments don't allow us to measure those short-term effects. See chart below. The instruments the EAA have in their well is an old-fashioned (oldie but goodie) analog chart recorder that records data continuously, and behaves similar to a seismograph.

My guess is that the instruments we use here (pressure transducers) lack the precision and have longer sampling frequency (we record hourly data) that don't allow us to measure these short-duration effects--although they almost certainly do occur here too. I've looked into this before at other wells for a few other quakes (Mexico, Chile etc) when the EAA recorded similar effects. We didn't see it in any of our wells for the same reason described above (I believe).

In addition, I looked at Barton Springs (gage and flow) and we also can't see any discernible effects. They record data every 15 minutes, but their instrumentation also samples at a certain frequency and the hydrologic setting (semiconfined? interference from pool fluctuations) may influence whether you can measure those effects at that location.

If we had a chart recorder, and perhaps if Barton Springs had instruments in the spring that measured water velocity, we might actually see a measureable change.

Click here for a Keye-TV interview about the quake. (no there is not a risk of large earthquakes in Central Texas).

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