Jieyuan Ning

Pole-Tide Modulation of Slow Slip Events at Circum-Pacific Subduction Zones

Episodic slow slip (ESS) events have been detected at several circum- Pacific subduction zones, such as Cascadia, Japan, and Mexico. Notably, at least eight ESS events along the northern Cascadia subduction zone recurred with a period of 13-16 months. We study the relationship between pole-tide (associated with Chan- dler wobble with a period of 14 months)-induced stress and the occurrence of the ESS events. Our quantitative analysis shows that 14 of the 20 documented ESS events occurred during the ascension phase, prior to the maximum, of a pole-tide-induced Coulomb failure stress change, and three events occurred at the stress-change peak. The pole tides modulate the stress field at the downdip edge of the transition zone along the plate interface and may trigger ESS events when conditions are favorable. The phase advance of the triggered events with respect to the induced Coulomb failure stress change may reflect that the fault slip is dictated by a rate- and state- dependent friction law inferred from laboratory experiments.

Upper mantle tomography in the northwestern Pacific region using triplicated P waves

We conducted delay time tomography of the upper mantle beneath the northwestern Pacific using P data from NorthEast China Extended SeiSmic Array, F-net, and nearby available stations. To improve resolution and accuracy in the vicinity of mantle discontinuities, we extracted traveltimes of both initial and secondary phases observed at triplication distances by using a waveform fitting technique. Compared with the model obtained by using only the initial phase, the resolution just above the 410 km discontinuity is especially improved, and low-velocity anomalies beneath the Changbai Volcano are clearly observed down to the 410 km discontinuity. Compared with previous models, low-velocity anomalies atop the 410 are more pronounced. The results of this study together with the previous receiver function analysis provide further support that we have hot material beneath the Changbai Volcano.

Simultaneous Determination of Crustal Thickness and P Wavespeed by Virtual Deep Seismic Sounding (VDSS)

The method of virtual deep seismic sounding (VDSS) uses the large amplitude, postcritical reflection off the Moho, the SsPmp phase, to probe the Moho. In this study, we augment VDSS using the change in differential travel times between phases SsPmp and Ss ( T ) as a function of distance (moveout) to determine simultaneously both the thickness ( H ) and overall P wavespeed ( V P ) of the crust. Tests using synthetic data show that for typical uncertainties in measuring T (1 standard deviation of ±0.2  s), a minimum uncertainty of ∼±1.1  km and ±0.06  km/s can be reached for nominal values of H and V P , respectively. We then demonstrate its utility with field data recorded by two permanent stations in Australia.