Adv Advanced anced Worksho shop p on n Ea Earthquake Fa Fault - PowerPoint PPT Presentation

Adv Advanced anced Worksho shop p on n Ea Earthquake Fa Fault Mechanics: The Theory, , Simulation on and Observation ons ICTP, Trieste, Sept 2-14 2019 Lecture 6: macroscopic source properties Jean Paul Ampuero (IRD/UCA Geoazur)

Overview Macroscopic source properties constrained by seismology: • seismic moment • source time function • corner frequency • radiated energy à stress drop, rupture speed, rupture size

Moment (N − m) on the fault Detailed space-time distribution of slip Outputs of dynamic rupture models : = 4.67 x 10 21 Nm =60.3 , =58.3 GT.DBIC. P 10 20 φ =77.1 ° , ∆ =71.8 E r = 5.16e+16 II.ASCN.00 P E r /M 0 = 1.10e − 05 = 67.7 s, T d = 109.5 s φ =89.4 ° , ∆ =58.4 f c = 5.2 mHz IU.TSUM.00 P 10 19 φ =108.8 ° , ∆ =85.9 n 0 = 1.46 II.SUR.00 P n 1 = 1.74, r 1 = 0.17 φ =122.3 ° , ∆ =85.1 n 2 = 1.58, r 2 = 0.23 II.HOPE.00 P 10 18 φ =151.5 ° , ∆ =47.6 σ p = 0.11 MPa IU.PMSA.00 P φ =174.6 ° , ∆ =48.9 10 − 3 10 − 2 10 − 1 10 0 120 140 IU.SPA.00 P Detailed source parameters φ =180.0 ° , ∆ =73.8 Frequency (Hz) IU.CASY.00 P φ =181.7 ° , ∆ =97.7 IU.SBA.00 P φ =190.7 ° , ∆ =80.1 4.9 G.DRV.00 P φ =192.7 ° , ∆ =93.6 IU.SNZO.00 P φ =224.5 ° , ∆ =94.8 IU.PTCN.00 P φ =250.6 ° , ∆ =53.2 Depth (km) 17.2 G.PPT. P φ =256.3 ° , ∆ =72.2 IU.KIP.00 P φ =292.1 ° , ∆ =90.8 CI.BAR. P = 310.0 , = 18.0 , = 63.0 676 + seismograms & ground displacements G.ECH. SH φ =41.4 ° , ∆ =96.0 ° 1143 IU.PAB.00 SH φ =46.4 ° , ∆ =85.1 ° 763 IU.LSZ.00 SH = 5.12 MPa φ =108.1 ° , ∆ =96.7 ° 1527 II.SUR.00 SH φ =122.3 ° , ∆ =85.1 ° = 3.05 MPa 794 IU.CASY.00 SH φ =181.7 ° , ∆ =97.7 °

From ground motion recordings … Seismograms = ground velocity

From ground motion recordings to the rupture process How much did the fault slip? How did it slip? Fast/slow? Smooth/tortuous? Loud/silent?

Moment (N − m) + seismograms & ground displacements on the fault Detailed space-time distribution of slip Outputs of dynamic rupture models : = 4.67 x 10 21 Nm =60.3 , =58.3 GT.DBIC. P 10 20 φ =77.1 ° , ∆ =71.8 E r = 5.16e+16 II.ASCN.00 P E r /M 0 = 1.10e − 05 = 67.7 s, T d = 109.5 s φ =89.4 ° , ∆ =58.4 f c = 5.2 mHz IU.TSUM.00 P 10 19 φ =108.8 ° , ∆ =85.9 n 0 = 1.46 II.SUR.00 P n 1 = 1.74, r 1 = 0.17 φ =122.3 ° , ∆ =85.1 n 2 = 1.58, r 2 = 0.23 II.HOPE.00 P 10 18 φ =151.5 ° , ∆ =47.6 σ p = 0.11 MPa IU.PMSA.00 P Fine vs. coarse source parameters φ =174.6 ° , ∆ =48.9 10 − 3 10 − 2 10 − 1 10 0 120 140 IU.SPA.00 P φ =180.0 ° , ∆ =73.8 Frequency (Hz) IU.CASY.00 P φ =181.7 ° , ∆ =97.7 IU.SBA.00 P φ =190.7 ° , ∆ =80.1 4.9 G.DRV.00 P φ =192.7 ° , ∆ =93.6 IU.SNZO.00 P φ =224.5 ° , ∆ =94.8 IU.PTCN.00 P φ =250.6 ° , ∆ =53.2 Depth (km) 17.2 G.PPT. P φ =256.3 ° , ∆ =72.2 IU.KIP.00 P φ =292.1 ° , ∆ =90.8 CI.BAR. P = 310.0 , = 18.0 , = 63.0 φ =331.2 = 2.40 km/s, Var. = 0.1772 IU.RSSD.00 P φ =336.7 = 29.6 km, H c = 18.1 km IU.CCM.00 P • • • • • Macroscopic source parameters : φ =343.5 IU.DWPF.00 P Average rupture speed Rupture duration Rupture size Seismic moment rate (source time function) Seismic moment φ =350.3 IU.SSPA.00 P φ =356.2 6.8 10.2 13.6 17.0 CN.SCHQ. SH Coseismic Slip(m) = 4.1 , =58.3 ° φ =356.2 ° , ∆ =56.7 ° 636 =71.8 ° 835 II.ASCN.00 P 0 30 60 =58.4 ° 481 IU.TSUM.00 P Time (s) =85.9 ° 527 =85.1 ° 717 II.HOPE.00 P =47.6 ° 384 IU.PMSA.00 P =48.9 ° 292 =73.8 ° 113 IU.CASY.00 P =97.7 ° 331 =80.1 ° 166 =93.6 ° 130 IU.SNZO.00 P =94.8 ° 543 IU.PTCN.00 P =53.2 ° 373 =72.2 ° 121

Distance along dip (km) G.ECH. SH 676 φ =41.4 ° , ∆ =96.0 ° Depth (km) − 40 17.2 1143 IU.PAB.00 SH φ =46.4 ° , ∆ =85.1 ° 763 IU.LSZ.00 SH ∆σ 0.15 = 5.12 MPa φ =108.1 ° , ∆ =96.7 ° II.SUR.00 SH 1527 ∆σ E = 3.05 MPa φ =122.3 ° , ∆ =85.1 ° 0 29.6 794 IU.CASY.00 SH φ =181.7 ° , ∆ =97.7 ° φ =331.2 = 2.40 km/s, Var. = 0.1772 IU.RSSD.00 P φ =336.7 Trade-offs in earthquake source studies = 29.6 km, H c = 18.1 km IU.CCM.00 P φ =343.5 IU.DWPF.00 P φ =350.3 IU.SSPA.00 P φ =356.2 Less uncertainty High fidelity 6.8 10.2 13.6 17.0 CN.SCHQ. SH Coseismic Slip(m) = 4.1 , =58.3 ° φ =356.2 ° , ∆ =56.7 ° 636 =71.8 ° 835 II.ASCN.00 P 0 30 60 =58.4 ° rate Moment 481 IU.TSUM.00 P Time (s) =85.9 ° 527 =85.1 ° 717 II.HOPE.00 P =47.6 ° 384 IU.PMSA.00 P =48.9 ° Time 292 =73.8 ° 113 IU.CASY.00 P =97.7 ° 331 =80.1 ° 166 =93.6 ° 130 IU.SNZO.00 P =94.8 ° 543 IU.PTCN.00 P =53.2 ° 373 =72.2 ° 121 High definition Moment (N − m) More detail = 4.67 x 10 21 Nm =60.3 , =58.3 GT.DBIC. P 10 20 φ =77.1 ° , ∆ =71.8 E r = 5.16e+16 II.ASCN.00 P E r /M 0 = 1.10e − 05 = 67.7 s, T d = 109.5 s φ =89.4 ° , ∆ =58.4 f c = 5.2 mHz IU.TSUM.00 P 10 19 φ =108.8 ° , ∆ =85.9 n 0 = 1.46 II.SUR.00 P n 1 = 1.74, r 1 = 0.17 φ =122.3 ° , ∆ =85.1 n 2 = 1.58, r 2 = 0.23 II.HOPE.00 P 10 18 φ =151.5 ° , ∆ =47.6 σ p = 0.11 MPa IU.PMSA.00 P φ =174.6 ° , ∆ =48.9 10 − 3 10 − 2 10 − 1 10 0 120 140 IU.SPA.00 P φ =180.0 ° , ∆ =73.8 Frequency (Hz) IU.CASY.00 P φ =181.7 ° , ∆ =97.7 IU.SBA.00 P φ =190.7 ° , ∆ =80.1 4.9 G.DRV.00 P φ =192.7 ° , ∆ =93.6 IU.SNZO.00 P φ =224.5 ° , ∆ =94.8 IU.PTCN.00 P φ =250.6 ° , ∆ =53.2 Depth (km) 17.2 G.PPT. P φ =256.3 ° , ∆ =72.2 IU.KIP.00 P φ =292.1 ° , ∆ =90.8 CI.BAR. P = 310.0 , = 18.0 , = 63.0

Source time functions

Global source studies Ye et al (JGR 2016) . 116 M7+ shallow subduction zone thrust earthquakes . finite source inversions with teleseismic data , 0.005-0.9 Hz Robust source time functions (STF, m oment rate) . Uniform method and careful manual analysis .

Global source studies Ye et al (JGR 2016) . 116 M7+ shallow subduction zone thrust earthquakes . finite source inversions with teleseismic data , 0.005-0.9 Hz Robust source time functions (STF, m oment rate) . Uniform method and careful manual analysis .

̇ STF from deconvolution seismogram = (Green’s function)*(Source Time Function) ! " ($) = ' " ($) ∗ * + ($) * means convolution G can be synthetic or empirical Deconvolution: infer ̇ * + ($) from ! " ($) SCARDEC (by Martin Vallée, IPGP): real-time STF from teleseismic data large catalog of past events new events posted rapidly on Twitter by @geoscope_ipgp

Teleseismic waves https://www.iris.edu/hq/inclass/fact-sheet/

Questions to address: • What are the common features of earthquakes? • Do small and large earthquakes start equal? • Are earthquakes self-similar at all magnitudes? • How are earthquakes different from each other? • Is there such a thing as a freak event? • What do those similarities and differences tell us about earthquake dynamics?

Enabled by global earthquake source products by Lingling Ye (Caltech), Martin Vallée (IPGP) and Gavin Hayes 5USGS)

G eneral patterns of Source Time Functions . Bin STFs by magnitude, 20 nearest neighbour s . In each bin, at each point in time, compute median STF

G eneral patterns of Source Time Functions Median STFs have linear onset, same for all magnitudes Mw>7.2

G eneral patterns of STFs . Normalize ze ea each ST STF by by it its dura rati tion Scale them such that they integrate to 1 . Compute median of normalized STF . On average, all STFs can be scaled to a very simple, quasi-triangular shape

On average (median), all STFs can be scaled to a very simple, quasi-triangular shape Meier, Ampuero and Heaton (2017)

Implications for moment / duration scaling Linear growth suggests M 0 ~ T 2 scaling In contrast to the widely reported M 0 ~ T 3 scaling à scaling break !

Why is linear moment rate growth surprising? Self-similar model for small earthquakes: ∆ ! Circular rupture with constant stress drop and constant rupture speed ! ̇ 0 ∝ % 2 ! Ruptures become elongated after they break the whole seismogenic width: moment grows s sl slower than quadratic But the linear trend ( ! " ~$ ) is observed after ~5 s, before rupture sa saturates s the se seism smogenic width Seismogenic width Slip rate (m/s)

Implications for Rupture Growth Scaling . Observed STF growth is linear !"# ∝ & 1 . If rupturing area grows as ! ( ! ) ∝ ! ! … and average slip grows as . ! ( ! ) ∝ ! ! . Seismic moment ! ! ( ! ) ∝ ! ( ! ) ! ( ! ) ∝ ! ! ! ! Moment rate exponent . ! = ! + ! − 1 Since we observe linear growth . ! !"# ~ 1 → ! + ! ~ ! ! !! = 2 + 1 = 3 . Self-similar pulse or crack à How can we lower the moment rate growth? Lower alpha, lower beta, or combination of both? . Pulse-like rupture with areas of systematic slip deficits? .

Intermediate-size event unzipping part of the lower edge of the coupled zone (Junle Jiang, Caltech) Nucleation Pre-stress Propagation Final stress Arrest

All M>7 subduction earthquakes 2015 Mw 7.8 Gorkha, Nepal earthquake ? Avouac et al (Nat Geo, 2015)

Thingbaijam et al (2017) All M>7 subduction earthquakes Rupture length ? 1 = e p o l S W x 2 Rupture width L x 2.8

Fluctuations around the median STF Fit a function to STFs: Multiplicative noise STF residuals in magnitude bins normalized by fitting function STF residuals

STF fluctuations are multiplicative and Gaussian Empirical cumulative distribution of STF residuals