Constraints on rupture speed of the 2001 MS 8.1 West Kunlun Mountain Pass earthquake by co-seismic surface rupture slip displacements based on the slip-weakening mechanism with frictional undershoot involved

With co-seismic surface rupture slip displacements provided by the field observation for the 2001 MS8.1 West Kunlun Mountain Pass earthquake, this paper estimates the rupture speed on the main faulting segment with a long straight fault trace on the surface based on a simple slip-weakening rupture model, in which the frictional overshoot or undershoot are involved in consideration of energy partition during the earthquake faulting. In contrast to the study of Bouchon and Vallée, in which the rupture propagation along the main fault could exceed the local shear-wave speed, perhaps reach the P-wave speed on a certain section of fault, our results show that, under a slip-weakening assumption combined with a frictional undershoot (partial stress drop model), average rupture speed should be equal to or less than the Rayleigh wave speed with a high seismic radiation efficiency, which is consistent with the result derived by waveform inversion and the result estimated from source stress field. Associated with the surface rupture mechanism, such as partial stress drop (frictional undershoot) associated with the apparent stress, an alternative rupture mechanism based on the slip-weakening model has also been discussed.

Imaging the rupture process of the 10 January 2018 Mw7.5 Swan island, Honduras earthquake

The 10 January 2018 Mw7.5 Swan island,Honduras earthquake occurred on the Swan island fault,which is a transform plate boundary between the North American and Caribbean plates.Here we back-project the rupture process of the earthquake using dense seismic stations in Alaska,and find that the earthquake ruptured at least three faults(three stages)for a duration of~40 s.The rupture speed for the longest fault(stage 3)is as fast as 5 km/s,which is much faster than the local shear wave velocity of~4 km/s.Supershear rupture was incidentally observed on long and straight strike-slip faults.This study shows a supershear rupture that occured on a strike-slip fault with moderate length,implying that supershear rupture might commonly occur on large strike-slip earthquakes.The common occurrence of supershear rupture on strike-slip earthquakes will challenge present understanding of crack physics,as well as strong ground motion evaluation in earthquake engineering.

RUPTURE OF THIN METAL TUBES BY NORMAL AND OBLIQUE IMPACT OF BLUNT CONICALNOSED MISSILES:EXPERIMENTS

Impact tests at both normal and oblique angles of incidence were conducted on thin mild tubes using a moderate size of 90 degrees conical-nosed missiles. The minimum impact speed that generated cracks through the thickness of the wall, termed the speed for rupture, was measured, and various modes of rupture were identified. For a thin tube hit by a missile at a normal angle of obliquity at the speed for rupture, the contact region spreads across the nose of the missile, and the transverse shear deformation is predominant in the final failure process. If the angle of obliquity is 30 degrees, the missile pierces a hole through the wall of the tube. At the speed for rupture, the kinetic energy of the missile for oblique angle 30 degrees is only about 45% that required for plugging at a normal angle of obliquity.

Bounding of near-fault ground motion based on radiated seismic energy with a consideration of fault frictional mechanisms

The energy radiated as seismic waves strongly depends on the fault rupture process associated with rupture speed and dynamic frictional mechanisms involved in the fault slip motion. Following McGarr and Fletcher approach, we derived a physics-based relationship of the weighted average fault slip velocity vs apparent stress, rupture speed and static stress drop based on a dynamic circular fault model. The resultant function can be approximately used to bound near-fault ground motion and seismic energy associated with near-fault coseismic deformation. Fault frictional overshoot and under- shoot mechanisms governed by a simple slip-weakening constitutive relation are included in our consideration by using dy- namic rupture models named as M- and D-models and proposed by Madariaga （1976） and Boatwright. We applied the above function to the 2008 great Wenchuan earthquake and the 1999 Jiji （Chi-Chi） earthquake to infer the near-fault ground motion called slip weighted average particle velocity and obtained that such model-dependent prediction of weighted average ground velocities is consistent to the results derived from the near-fault strong motion observations. Moreover, we compared our re- sults with the results by McGarr and Fletcher approach, and we found that the values of the weighted average particle veloci- ties we obtained for these two earthquakes are generally smaller and closer to the values by direct integration of strong mo- tion recordings of the near-fault particle velocity waveform data. In other words, if this result comes to be true, it would be a straightforward way used to constrain the near-fault ground motion or to estimate source parameters such as rupture speed, static and dynamic stress drops.