1 / 17

Guided Seismic Waves from the Indonesian Subduction Zone to the Australian Craton

Guided Seismic Waves from the Indonesian Subduction Zone to the Australian Craton. T. Furumura Earthquake Research Institute, University of Tokyo B.L.N. Kennett Research School of Earth Sciences, The Australian National University. Stochastic wave guides in continental lithosphere.

skule
Download Presentation

Guided Seismic Waves from the Indonesian Subduction Zone to the Australian Craton

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Guided Seismic Waves from the Indonesian Subduction Zone to the Australian Craton T. Furumura Earthquake Research Institute, University of Tokyo B.L.N. Kennett Research School of Earth Sciences, The Australian National University

  2. Stochastic wave guides in continental lithosphere • Seismic wave propagation from the Indonesian subduction zone into cratonic Australian lithosphere shows a characteristic of low frequency onsets followed by a long duration high frequency coda • Such effects are observed at the permanent array WRA and at portable stations • The detailed character depends on the source position along the subduction zone system WRA ERI ANU

  3. P and S coda at WRA from Banda Sea event ERI ANU

  4. Record Sections of P and S arrivals with complex coda ERI ANU

  5. Onsets of scattered arrivals showing frequency separation ERI ANU

  6. Strong stochastic waveguide effects D C B A Many paths into Northern Australia show strong high frequency coda for both P and S waves with very high Q. Similar effects are also seen from Australian sources to stations further south. ERI ANU

  7. Subduction zone structure variations The nature of the transition between the thick Australian Lithosphere and the subduction zone varies with position along the arc as illustrated here in sections from the model of Widiyantoro & van der Hilst (1997) The character of the seismic records at stations in Northern Australia depend on the source location and the structural setting Zone A B C D ERI ANU

  8. Examples of seismogram character: zone A 3-component frequency-time analysis showing slow decay of high frequency coda for both P and S waves ERI ANU

  9. Examples of seismogram character: zones A,B A B The rate of decay of high frequency arrivals is slightly slower for sources in zone B, but in each case the P coda is still significant at the arrival of S ERI ANU

  10. Examples of seismogram character: zones C,D D C The longest coda trains tend to come from Banda Sea events where the Australian lithosphere abuts the subduction zone. P coda tends to be particularly strong in zone D, which may be related to a change in focal mechanisms. ERI ANU

  11. 2D FDM Simulation with stochastic random heterogeneities -njp3 Australian standard model -earth flattening - Dx/Dz=62.5m/62.5m - 16th-order Staggered-grid - Parallel FDM - Double-couple source, 16Hz (then convolved with 6Hz triangle SVF) - ES 32node 5hour Stochastic Random Heterogeneity: VK Upper Crust: 5.0 / 0.25 (Ax/Az, km) Lower Crust: 5.0 / 0.25 Mantle 1: 20.0 / 0.5 Mantle 2: 20.0 / 0.5 WRA Crust Mantle 1 100. Mantle 2 Depth [km] 200. 300. 1500. 1000. 500. 0. Distance [km] ERI ANU 150.

  12. 2D FDM Simulation with stochastic random heterogeneities WRA WRA WRA P/SV Wave Crust Mantle 1 100. Mantle 2 Depth [km] 200. 300. Movie 1500. 1000. 500. 0. Distance [km] ERI ANU

  13. Effect of Mantle Q Crust Mantle 1 Mantle 2 The development of high-f coda is rather insensitive to Q in Mantle 1/2. With very low-Q in the mantle, a change in amplitude and coda decay appears. ERI ANU

  14. Crust and Mantle Heterogeneity Crust Mantle 1 Mantle 2 Larger heterogeneity in the lower crust enhances coda amplitude and duration very significantly, but the effect is rather mild for the Mantle. ERI ANU

  15. Models of transition from subduction zone to craton Neck model 120 E (A) Base model 125 E (B) Wedge model 130 E (C) Wedge2 model 135 E (D) ERI ANU

  16. Effect of structure at the subduction zone Base B A Neck C Wedge D Wedge2 The nature of the structure between the subduction zone and the Australian craton plays an important role in developing both a large and lengthy coda for P and S. ERI ANU

  17. Guided wave effects • The 2-D simulations to high frequency capture many of the characteristics of the observed seismograms • Comparisons of 2-D and 3-D calculations suggest that with the propagation along the grain of heterogeneity the coda duration and amplitude will be well approximated • A combination of mantle heterogeneity and lower crustal heterogeneity is needed to achieve the long durations and sustained frequency content of the P and S codas • The nature of the transition structure from the subduction zone to the Australian craton influences the character of the arrivals. ERI ANU

More Related