Research
2014–15:
Long-term acceleration of aseismic slip preceding the 2011 Mw 9 Tohoku-oki earthquake: Constraints from repeating earthquakes
A decadal-scale deformation transient preceding the 2011 Mw 9 Tohoku-oki, Japan earthquake was reported from continuous GPS data and interpreted as accelerating aseismic slip on the Japan Trench megathrust. Given the unprecedented nature of this transient, independent confirmation of accelerating slip is required. In this project we show that changes in the recurrence intervals of repeating earthquakes on the Japan Trench megathrust in the period 1996 to 2011 are consistent with accelerating slip preceding the Tohoku-oki earthquake. All sequences of repeating earthquakes with statistically significant trends in recurrence interval offshore south-central Tohoku occurred at an accelerating rate. Furthermore, estimates of the magnitude of slip acceleration from repeating earthquakes are consistent with the completely independent geodetic estimates. From a joint inversion of the GPS and seismicity data, we infer that a substantial portion of the megathrust experienced accelerating slip, partly surrounding the eventual rupture zone of the Mw 9 earthquake.
Publication:
Mavrommatis, A.P., Segall, P., Uchida, N., and K.M. Johnson (2015, accepted). Long-term acceleration of aseismic slip preceding the Mw 9 Tohoku-oki earthquake: Constraints from repeating earthquakes, Geophysical Research Letters. doi: 10.1002/2015gl066069 [ link
], SCEC 2015 [ poster ], AGU 2015 [link coming soon].
2012–14:
Decadal-scale transient deformation prior to the 2011 Mw 9 Tohoku-oki earthquake
GPS time series in northeast Japan exhibit nonlinear trends from 1996 to 2011 before the Mw 9.0, 2011 Tohoku-oki earthquake. After removing reference frame noise, we model time series as linear trends plus constant acceleration, correcting for coseismic and postseismic effects from the numerous Mw ~ 6.5+ earthquakes during this period. We find spatially coherent and statistically significant accelerations throughout northern Honshu. Large areas of Japan outside the Tohoku region show insignificant accelerations, demonstrating that the observation is not due to network-wide artifacts. While the accelerations in northern Tohoku (Sanriku area) can be explained by decaying postseismic deformation from pre-1996 earthquakes, the accelerations in south-central Tohoku appear unrelated to postseismic effects. The latter accelerations are associated with a decrease in average trench-normal strain rate and can be explained by increasing slip rate on the Japan trench plate interface and/or updip migration of deep aseismic slip in the decades before the 2011 Tohoku-oki earthquake.
Publication:
Mavrommatis, A.P., Segall, P., and K.M. Johnson (2014). A decadal-scale deformation transient prior to the 2011 Mw 9.0 Tohoku-oki earthquake, Geophysical Research Letters, 41, doi: 10.1002/2014GL060139. [ link
| pdf ]
The paper was selected as an Eos Research Spotlight and a UNAVCO Science Snapshot.
Press coverage: Stanford News, Real Clear Science, Science Daily, and phys.org
Conference presentations:
SCEC 2012 [ link
]
COLLABORATIONS & CONTRIBUTIONS
2013–2016:
Overlapping coseismic and postseismic slip on the northern Japan subduction interface
Study led by Kaj Johnson (Indiana University).
The canonical model of fault coupling assumes slip is fully partitioned into fixed asperities that display stick-slip behavior and regions that creep stably. We show that this simple asperity model is inconsistent with GPS measurements of deformation in northern Japan associated with interseismic coupling on the subduction interface and the transient response to M6.3-7.2 earthquakes from 1998-2011. Comparisons of GPS data with simulations of earthquakes surrounded by velocity-strengthening creep requires that afterslip following moderate earthquakes overlap areas of the fault that ruptured in previous earthquakes, including the 2011 M9 Tohoku-oki mega-thrust earthquake. We find that fully locked model asperities must be roughly 50% smaller than determined by source inversions to be consistent with the observed post-seismic deformation. These smaller asperities are consistent with strain accumulation in 2009, although more extensive locking is required a decade earlier in 1998.
Publication:
Johnson, K.M., Mavrommatis, A.P., and P. Segall (2016). Small interseismic asperities and widespread aseismic creep on the northern Japan subduction interface, Geophysical Research Letters.
Conference presentation: AGU 2013
2015–2016:
Paleogeodesy of the Southern Santa Cruz Mountains Frontal Thrusts, Silicon Valley, CA
Study led by Felipe Aron (Stanford University).
We have developed a method to infer long-term fault slip rate distributions using topography, by coupling a three-dimensional elastic boundary element model with a geomorphic incision rule. We used a 10 m-resolution digital elevation model (DEM) to calculate channel steepness (ksn) throughout the actively deforming southern Santa Cruz Mountains in Central California. We then used these values with a power-law incision rule and the Poly3D code to estimate slip rates over seismogenic, kilometer-scale thrust faults accommodating differential uplift of the relief throughout geologic time. Implicit in such an analysis is the assumption that the topographic surface remains unchanged over time as rock is uplifted by slip on the underlying structures. The fault geometries within the area are defined based on surface mapping, as well as active and passive geophysical imaging. Fault elements are assumed to be traction-free in shear (i.e., frictionless), while opening along them is prohibited. The free parameters in the inversion include the components of the remote strain-rate tensor (εij) and the bedrock resistance to channel incision (K), which is allowed to vary according to the mapped distribution of geologic units exposed at the surface. The nonlinear components of the geomorphic model required the use of a Markov chain Monte Carlo method, which simulated the posterior density of the components of the remote strain-rate tensor and values of K for the different mapped geologic units. Interestingly, posterior probability distributions of εij and K fall well within the broad range of reported values, suggesting that the joint use of elastic boundary element and geomorphic models may have utility in estimating long-term fault slip-rate distributions. Given an adequate DEM, geologic mapping, and fault models, the proposed paleogeodetic method could be applied to other crustal faults with geological and morphological expressions of long-term uplift.
Conference presentations:
SCEC 2015, AGU 2015.
2011–12:
Faulting processes during early-stage rifting: seismic and geodetic analysis of the 2009-2010 Northern Malawi earthquake sequence
Contribution to study led by James Gaherty (Lamont-Doherty Earth Observatory) and in collaboration with Matt Pritchard (Cornell University).
Conference presentation: AGU 2012
COLLABORATORS
Paul Segall (Stanford University) 2011 – present
Kaj Johnson (Indiana University) 2013 – present
Naoki Uchida (Tohoku University) 2013 – present
Felipe Aron (Stanford University) 2015 – present
Andrew Bradley (Stanford University, now Sandia National Labs) 2011 – 2014
Yo Fukushima (Kyoto University) 2012 – 2013
Shin'ichi Miyazaki (Kyoto University) 2012
Matt Pritchard (Cornell University) 2010 – 2011
Rowena Lohman (Cornell University) 2010 – 2011
William Barnhart (Cornell University, now University of Iowa) 2010 – 2011