When Good Quakes Go Bad Or How Do

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When Good Quakes Go Bad Or How Do Small Quakes End Up Being Big And Why Can’t Something Be Done About It? David Oppenheimer Presented to CISN Steering and Advisory Committees at Caltech, 27 September 2007

Where do Noise Events Come from? • Case 1 – Bad radio repeater at Oroville causes interference on 7 stations – Automated picks associate into Cape Mendocino “quake” – Coda durations last for 300 -400 s (M 5)

Where do Noise Events Come from? • Case 2 – Small quake occurs at Geysers – Automated “picks” are ok, but Oroville noise adds 2 bad picks. – No codas on BG stations. Oroville again causes codas of 300 -400 s (M 5)

Chronology of Event #40201796 Time (GMT) (hr: mn: sec) 05: 32: 46 05: 33: 38 05: 35: 44 05: 39: 09 05: 40: 05 05: 41: 06 05: 41: 33 Elapsed (mn: sec) 00: 00 00: 52 02: 58 06: 23 07: 19 08: 20 08: 47 Action Md 5. 0 issued V 01 Ml 1. 9 update V 02 Shake. Map V 01 Delete message Shake. Map V 02 Shake. Map V 03 Shake. Map delete

Solutions • Make picker smarter • RT differentiation of noise from signal • Squash bad magnitudes faster • Stifle Shake. Cast generation

Making systems smarter

Making systems smarter… Or, better, eliminate the problem

What have we learned? • Fine tune criteria for generating Shake. Maps • Shake. Cast needs to get smarter • Need to dynamically remove bad stations from system • Clients ascribe (too? ) high level of reliability to CISN products. • CISN staff should work with clients to explain limitations

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