NOAA Hydroacoustic recordings of an EPR Swarm

1
NOAA Hydroacoustic recordings of an EPR Swarm
EPR and Salton Trough Transform Fault Seismicity
Cataloged Strike Slip Swarms
Mw 5.8
Mw 5.9
Mw 5.9
Mw 5.8

• Swarms with durations of hours to days and
  maximum magnitudes ranging from 4 to 6 dominate
  strike slip faults from the EPR to the Salton
  Sea.

2
EPR Transform Fault Prediction Algorithm
If for 5.5 years, starting on on May 23rd, 1996,
every time there was a Mgt2.5 (i.e. ASLgt207)
earthquake on the Discovery or Gofar faults, you
issued a prediction of a magnitude 5.4-6.2
earthquake within 15 km and one hour of the
potential foreshock, you would have achieved a
probability gain of 500-1000
3

• 2005 Swarm
• Obsidian Buttes

M 5.1
Largest EQ M 5.1 Total M 5.3
4

• Microseismicity Migration and Geodetic
  Deformation Signals precede the
• largest EQ

M 5.1 EQ
5
InSAR Data Synthetics
6
Aseismic Fault Slip Model
profile
Aseismic slip shallower than seismicity
Lohman and McGuire, 2006
7
Stressing rate and seismicity

• Assume stressing-rate history
• Exponential decay
• Vary As
• Prefer range 15-25
• Vary stress jump magnitude
• Consistent with InSAR coulomb stress change
• 3bars/5 days

8
Previous Swarms
9
New GPS

• This study
• CRRS-GLRS
• New PBO stations in October 2005
• Could constrain swarm evolution next time

Swarm
10
The Galapagos Transform

• Two major swarm episodes in t-phase catalog,
  one of which was also recorded by a temporary
  seismometer array on the islands.
• The magnitude vs time pattern cannot be
  explained by a superposition of aftershock
  sequences

Roland et al., 2004