Rapid determination of the magnitude and tsunami potential of large earthquakes, and implications for source physics 1. Mwpd and high-frequency, apparent rupture duration T0 2. Tsunamigenic earthquakes: T0 > 50s 3. P-wave dominant period calculation Td 4. Tsunamigenic earthquakes: the Td∙T0 discriminant 5. Importance of identifying length and depth of faulting
Anthony Lomax
ALomax Scientific, Mouans-Sartoux, France
Alberto Michelini Istituto Nazionale di Geofisica e Vulcanologia Roma, Italy
Mwpd and high-frequency, apparent rupture duration T0
Amplitude
HF Rupture Duration, T0 Duration
2 min
Mwpd processing steps: 12 September 2007, M8.4 Sumatra
(Lomax & Michelini 2009A) velocity seismogram
1.5 Hz, HF seismogram T0 T0 estimate: HF envelope
Mwp
ground-displacement M0 estimate: integral of displacement over duration T0
Mwpd OT+8-15min
Duration-amplitude magnitude Mwpd Raw Mwpd compared to MwCMT for 79 recent, large earthquakes. 9.5
interplate thrust events ▼ tsunami earthquakes ■ other event types ♦
9.0
Mwpd
8.5 8.0 7.5 7.0 6.5 6.0 6.0
6.5
7.0
7.5
8.0
MwCMT
8.5
9.0
9.5
Duration-amplitude magnitude Mwpd Raw Mwpd compared to MwCMT for 79 recent, large earthquakes. 9.5
interplate thrust events ▼ tsunami earthquakes ■ other event types ♦
9.0
Mwpd
8.5
Raw Mwpd underestimates MwCMT for largest interplate thrust and tsunami earthquakes
8.0 7.5 7.0 6.5 6.0 6.0
6.5
7.0
7.5
8.0
MwCMT
8.5
9.0
9.5
Duration-amplitude magnitude Mwpd with moment scaling Comparison of MwCMT with Mwpd corrected with moment scaling for interplate thrust and tsunami earthquakes.
Mwpd (moment scaled)
9.5
interplate thrust events ▼ tsunami earthquakes ■ other event types ♦
9.0
M
pd 0
= M 0 M 0 / M
cutoff 0.4 0
M0cutoff ≈7.5x1019 N-m (equivalent to Mw≈ 7.2)
8.5 σ = 0.11 m.u.
8.0
Mwpd
7.5
OT+8-15min
MwCMT
7.0
OT+30min 6.5 6.0 6.0
6.5
7.0
7.5
8.0
MwCMT
8.5
9.0
9.5
Implications of moment scaling: large earthquake rupture Moment scaling → deficiency in down-going (teleseismic) P-wave amplitude and energy
less mass in upper plate
destructive interference of pP or sP waves with down-going P waves
Implications of moment scaling: large earthquake rupture Moment scaling → deficiency in down-going (teleseismic) P-wave amplitude and energy → trapped energy... re-absorbed at rupture front? helps to drives rupture?
Discriminating Tsunamigenic earthquakes: T0 > 50s
broadband
50s
2006, Mw7.7, T0=180s, It=19
Indonesia tsunami earthquake
HF 1-5Hz
50s broadband
2009, Mw7.6, T0=39 s, It=1 Tonga Islands
HF 1-5Hz
Discriminating Tsunamigenic earthquakes: T0 > 50s
broadband
50s
2006, Mw7.7, T0=180s, It=19
Indonesia tsunami earthquake
T0>>50s HF 1-5Hz
50s broadband
2009, Mw7.6, T0=39 s, It=1
T050s exceedance estimate Td∙T50Ex discriminant
Mwp
Tdominant (sec)
To>50s Exceedance
Event location
http://s3.rm.ingv.it/
Real-time monitor: Tonga Islands 2009, Mw7.6, T0=39s, It=1 INGV monitor simulation, IRIS realtime data, OT+9min, rapid To>50s exceedance estimate Td∙T50Ex discriminant
Mwp
Tdominant (sec)
To>50s Exceedance
Event location
http://s3.rm.ingv.it/
Importance of identifying length and depth of faulting Two ruptures with similar seismic potency LWD
1 e r u t rup
z Mo = μLWD; μ ∝ z “seismic” faulting model Mo1 ≤ Mo2 p ru
e t ur
2
Importance of identifying length and depth of faulting Tsunami potential ← seafloor uplift: “tsunami” faulting model (Satake 1994)
ru
loor f a e s 1 e r u t p
t uplif
L1 z
if t l p ru o o l f sea
Mo = μLWD; μ ∝ z “seismic” faulting model Mo1 ≤ Mo2 p ru
e t ur
2
L2
Importance of identifying length and depth of faulting rupture duration: To ← L / Vr ; Vr ∝ z → To grows with increasing L and decreasing z → TdTo discriminant identifies seafloor uplift, “tsunami” faulting model (Satake 1994)
ru
loor f a e s 1 e r u t p
t uplif
“tsunami” faulting model TdTo1 >> TdTo2
L1 z
if t l p ru o o l f sea
Mo = μLWD; μ ∝ z “seismic” faulting model Mo1 ≤ Mo2 p ru
e t ur
2
L2
Rapid determination of the magnitude and tsunami potential of large earthquakes, and implications for source physics The duration-amplitude magnitude Mwpd: available
