Origin of intraplate earthquakes
- 1. Geodynimacs Term Project Origin of Intraplate Earthquakes Jia Zhang 12.01.2016
- 2. Geodynimacs Term Project Outline Introduction Case studies 1.Intraplate Earthqukes in North China 2.Intraplate Earthquake in New Madrid Seismic Zone Unified model for intraplate earthqukes in the world Conclusions CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 2
- 3. Geodynimacs Term Project Introduction CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 3
- 4. Geodynimacs Term Project CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 4 understanding of how strain accumulates/releases and what the associated seismic potential and hazard are
- 5. Geodynimacs Term Project Proposed mechanisms pre-existing zones of weakness I. localized build-up of stress, i.e. stress amplification near plutons(Champion,1977); II. superposition of a triggering stress, i.e. postglacial rebound(Basham,1977) reduction of strength by mechanical and/or chemical means, i.e. increased pore pressure or hydrolytic weakening (Talwani, 1985) CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 5
- 6. Geodynimacs Term Project Case study 1/2 Intraplate Earthqukes in North China Seismicity Velocity Filed CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 6
- 7. Geodynimacs Term Project CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 7 Case study 1/2
- 8. Geodynimacs Term Project Case study 1/2 Spatiotemporal patterns of the intraplate earthquakes Ⅰ Long-distance roaming CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 8
- 9. Geodynimacs Term Project Case study 1/2 Spatiotemporal patterns of the intraplate earthquakes Ⅱ Fault coupling and interaction CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 9
- 10. Geodynimacs Term Project Case study 1/2 Geodynamic Modelling CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 10
- 11. Geodynimacs Term Project Case study 1/2 Geodynamic Modelling CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 11
- 12. Geodynimacs Term Project Case study 1/2 Stress Evolution and Triggering of Large Earthquakes in North China CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 12
- 13. Geodynimacs Term Project Intracontinental deformation in China and the associated seismicity are strongly influenced by the Indo-Asian collision. western China: indentation of the Indian plate; central and east china: the compressive stress arising from gravitational spreading of the Tibetan; High strain rates and intense seismicity within the circum-Ordos rifts the weakness in the crust; 80% of large (M ≥ 6.5) earthquakes have occurred within regions of increased earthquake-triggered Coulomb stresses. CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 13 Case Study 1/2
- 14. Geodynimacs Term Project Case Study 2/2 Intraplate Earthquake in New Madrid Seismic Zone hypotheses: crustal weakness zone(Sykes,1978) localized stress concentration (Stuart,1994) low cumulative lithospheric strength resulting from relatively high temperatures at depth (Liu and Zoback,1997) CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 14 Chen et al, 2014
- 15. Geodynimacs Term Project Case study 2/2 Hotspot origin of Mississippi Embayment CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 15Cox et al. 2002
- 16. Geodynimacs Term Project Case study 2/2 Heat Flow and Geotherms in NMSZ and Surrounding Area CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 16 Liu et al. 1997
- 17. Geodynimacs Term Project Case study 2/2 Lithospheric Strength Models for the NMSZ and Surrounding Region CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 17 Liu et al. 1997
- 18. Geodynimacs Term Project Case study 2/2 CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 18
- 19. Geodynimacs Term Project CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 19 Case study 2/2
- 20. Geodynimacs Term Project Triggering mechanism Sudden seismicity increase during the Holocene: Deglaciation trigger (Zoback et al. 2001) Weak zone in NMSZ: a residual thermal dome (Liu et al. 1997) associated with the passage of the Bermuda hotspot during early Late Cretaceous time (Cox et al. 1997). CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 20 Case study 2/2
- 21. Geodynimacs Term Project CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 21 the perturbation caused by ice loading is to suppress seismicity, whereas ice melting enhances seismic strain release. Case study 2/2
- 22. Geodynimacs Term Project Unified model for intraplate earthqukes two orders of stress in the continental lithosphere: 1. first-order stress field, extending over thousands of kilometers, is associated with plate tectonic forces. 2. second-order stress fields is superposed on the regional stresses with wave lengths of hundreds of kilometers associated with specific geologic and tectonic features. a stress buildup at suitable geological features, referred as Local Stress Concentrators in response to a uniform far-field regional stress field, associated with plate margin forces. CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 22
- 23. Geodynimacs Term Project Unified Model Inferring crustal stress magnitudes from stress rotations CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 23
- 24. Geodynimacs Term Project Unified Model Intraplate earthquake occurs when magnitude of SL approaches that of the regional stress, ST. This buildup of SL and its interaction with ST can result in a detectable rotation. CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 24 Talwani, 2015
- 25. Geodynimacs Term Project CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 25 Faults and local stress directions in the NMSZ (Johnson et al, 2014) local stress SL associated with the LSC (the intersection of BF and RF, solid lines) and SF has a clockwise rotation of 27° relative to ST(Talwani, 2015) Unified Model
- 26. Geodynimacs Term Project Temporal growth of SL as a predictor of earthquakes? with uncertainties in focal mechanisms, the accuracy with which γ can be detected is 15° Apparent absence of strain accumulation GPS measurements in the NMSZ have failed to provide a consensus that such pockets of elevated strain rate exist CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 26 Unified Model Constrains and improvement needed
- 27. Geodynimacs Term Project Conclusion Roaming and aperiodicity of intraplate earthquakes Mechanism Hypothesis: Weakness zone & Localized stress concentration Unified model: build up of pockets of local stress accumulation and interacts with regional stress may lead to the seismicity CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 27
- 28. Geodynimacs Term Project Conclusion Tectonic loading in mid-continents is shared by a complex system of interacting faults Reid’s elastic rebound theory: cycles of energy accumulation and release on a given fault. CENTER FOR EARTHQUAKE AND RESEARCH INFORMATION 28 Calais et al. 2016
Editor's Notes
- #4: recurrence time is longer; rarely recognized at the surface; release more stress; shallow location
- #23: Two general types of models: the localizing structures close to failure and a small stress perturbation, due to a regional stress source[erosion or deposition at the surface (Calais et al. 2010), glacial isostatic adjustment (Zoback 1992), stress transfer to the brittle upper crust (Liu and Zoback 1997)], triggered the earthquake; observed spatial association of Eqs with identifiable geologic features, e.g., with buried plutons (Long 1976), and buried rift pillows (Zoback and Richardson 1996) not address the basic cause of the stress buildup that brought the structure close to failure.
- #25: Fig. 1 In an intraplate setting the interaction of the local stress, SL, associated with the local stress concentrator (LSC), with the uni- formregional stress field ST, causes the final (ambient) stress, SF,to be rotated by γ° with respect to the regional stress field. The direction of SF is determined by in situ measurements or by the inversion of focal mechanism data
- #26: when the magnitude of this local stress buildup is comparable with the regional stress, it can lead to seismicity.
- #27: a temporal increase in SL manifests itself as an increase in the associated rotation, γ . Conversely, after a major earthquake and a release of the accumulated stress there will be a decrease in both SL and γ . Currently, with uncertainties in focal mechanisms, the accuracy with which γ can be detected is 15° the presence of local stress build-up in the vicinity of LSCs should be associated with local pockets of elevated strain. However, two decades of GPS measurements in the NMSZ have failed to provide a consensus that such pockets of elevated strain rate exist
- #29: However, tectonic loading in mid-continents is shared by a complex system of interacting faults spread over a large region