Geochemistry, Geophysics, Geosystems, Jul 4, 2014
Normal faulting earthquakes play an important role in the deformation of continents, and pose sig... more Normal faulting earthquakes play an important role in the deformation of continents, and pose significant seismic hazard, yet important questions remain about their mechanics. We use InSAR and bodywave seismology to compute dislocation models and centroid moment solutions for four normal-faulting earthquakes (Mw 5.7–6.2) that occurred in the Pumqu-Xainza Rift (PXR), southern Tibet, a region where lowangle normal faulting has previously been inferred. We also use the fault locations and slip to investigate the correlation between earthquakes and surface topography, and to calculate stress interactions between the earthquakes. The InSAR and body-wave models give consistent focal mechanisms except for the magnitude of the 1996 event, which may be overestimated due to postseismic deformation in the long-interval interferograms. We calculate the static stress changes due to coseismic slip and find that the 1993 event was too distant to cause triggering of the later events, but that the 1998 event pair occurred in regions of increased Coulomb stress resulting from the 1996 event. All the fault planes found here dip at 40–60, reinforcing the absence in observations for low-angle normal faulting earthquakes (dip < 30) whose focal planes can be determined unambiguously. The fault planes of the 1993 and 1996 events are not associated with any obvious surface geomorphology, suggesting that sometimes it is unreliable to resolve the focal plane ambiguity by geomorphology, even for Mw 6.2 events. Furthermore, these events occurred outside the center of the rift, indicating that the active faulting is more distributed and over a length-scale at least 25–50 km east-west in extent, rather than confined to the 20 km width seen in the current mapped faulting and topography. These results suggest that seismic hazard in other extensional zones worldwide might also be more broadly distributed than suggested by geomorphology.
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lithosphere is predominantly in the upper seismogenic layer. However, the distribution of geodetic observations is biased towards weaker areas, and faults can also modify the local rheology. Postseismic results could therefore be sampling weak regions within an otherwise strong crust or mantle."
sorts of boundaries.We hope that this response to our commentary will not undermine let alone deter the efforts of applied scientists engaging in interdisciplinary research with practitioners."
The most damaging natural disasters occur at the intersection between the world's poorest citizens and environmental hazards such as earthquakes, floods or drought. These hazards have a disproportionate impact on communities in the global South where people often lack the financial capacity to cope with, or be resilient to, the hazards they face (Kahn 2005).
In 2011 two significant earthquakes tested the world's most seismically resilient communities: the Christchurch earthquake in New Zealand and the Tohoku earthquake in Japan. These events challenged some of the best enforced, high-quality seismic building codes in the world and shocked two resilient communities. Although both countries coped extremely well, the concern lies with the many seismically vulnerable countries that are becoming rapidly industrial and urban centric. This commentary briefly examines the Christchurch and Tohuku earthquakes and considers what makes a community resilient and what can be learnt about resilience from ‘disasters’ in the global North? That is not to say that the global North's way is the only path to resilience, but if patterns of urbanisation continue to be emulated by the global South, some of the practices regarding built resilience should also be equally copied."
lithosphere is predominantly in the upper seismogenic layer. However, the distribution of geodetic observations is biased towards weaker areas, and faults can also modify the local rheology. Postseismic results could therefore be sampling weak regions within an otherwise strong crust or mantle."
sorts of boundaries.We hope that this response to our commentary will not undermine let alone deter the efforts of applied scientists engaging in interdisciplinary research with practitioners."
The most damaging natural disasters occur at the intersection between the world's poorest citizens and environmental hazards such as earthquakes, floods or drought. These hazards have a disproportionate impact on communities in the global South where people often lack the financial capacity to cope with, or be resilient to, the hazards they face (Kahn 2005).
In 2011 two significant earthquakes tested the world's most seismically resilient communities: the Christchurch earthquake in New Zealand and the Tohoku earthquake in Japan. These events challenged some of the best enforced, high-quality seismic building codes in the world and shocked two resilient communities. Although both countries coped extremely well, the concern lies with the many seismically vulnerable countries that are becoming rapidly industrial and urban centric. This commentary briefly examines the Christchurch and Tohuku earthquakes and considers what makes a community resilient and what can be learnt about resilience from ‘disasters’ in the global North? That is not to say that the global North's way is the only path to resilience, but if patterns of urbanisation continue to be emulated by the global South, some of the practices regarding built resilience should also be equally copied."