Rapid rupture and complex faulting of the May 12, 1990, Sakhalin deep earthquake: Analysis of regional and teleseismic broadband data

Abstract

A large (Mw=7.1) deep earthquake (606 km) occurred beneath Sakhalin Island, about 200 km away from the nearest well‐defined Wadati‐Benioff zone in southwestern Kurile. Moment tensors obtained in various frequency bands using the teleseismic data show that the Sakhalin event produced double‐couple radiation over a very broadband frequency range, and the P waveforms appear simple at most teleseismic stations (Δ=30–90°). On the other hand, many broadband seismometers successfully recorded the seismic waves at regional distances (Δ=3–25°) in Japan, showing two significant arrivals in the P wave seismograms whose time interval is about 3 s. The two P wave arrivals have the same polarity, the same apparent velocity, and similar amplitudes, which suggests that the two arrivals are the result of two sub‐events in the source process of the Sakhalin event. Analysis of the regional and teleseismic waveform data suggests an anomalously rapid slip propagation in the source process of the Sakhalin deep event. The difference in P waveform between the regional and teleseismic stations can be explained by having a long distance (>14–15 km) and short time interval (<1.5–2 s) between the two subevents, which implies that the apparent rupture velocity is larger than the S wave velocity unless the two subevents occurred simultaneously. The observation that the source duration of the Sakhalin event is shorter than those of other deep events of the same size supports the notion of rapid slip‐propagation for the Sakhalin event.

Fault plane orientations of intermediate‐depth and deep‐focus earthquakes in the Japan‐Kuril‐Kamchatka subduction zone

“…After accounting for the errors bars, only one of our earthquakes (event 12) can be categorized as having a supershear rupture, while several other earthquakes possibly have supershear rupture velocities. Supershear rupture has previously been observed for other deep earthquakes, including the 12 May 1990 [ Kuge , ] and 24 May 2013 M W 6.7 events [ Zhan et al , ] in our study area, and may be an actual characteristic of some ruptures. Rupture can propagate quickly when the fracture energy is low and most of the energy is radiated away rather than used to break or melt rock.…”

“…This hypothesized vertical tear is associated with rotated focal mechanisms and a fold in the slab geometry [ Myhill , ]. Several deep‐focus earthquakes also ruptured along subhorizontal planes [ Kuge , ; Glennon and Chen , ; Chen et al , ; Antolik et al , ; Tibi et al , ; Chen and Wen , ]. However, an M W 6.7 aftershock of the previously mentioned 24 May 2013 Sea of Okhotsk earthquake may have slipped on a vertical plane [ Zhan et al , ].…”

Rupture velocity estimation of large deep‐focus earthquakes surrounding Japan

“…Rupture velocities as a function of thermal parameter. Triangles indicate the values from Tibi et al [2003], asterisks are from Kuge [1994] and Wu and Chen [2001], and circles are for the values in this study.…”

Implications of seismic waveforms: Complex physical properties associated with stagnant slab

“…However, the P waveform of T1 (Δ∼14.5°) shows anomalously long duration (∼12 sec) or broadening and cannot be synthesized with M3.11 although the seismic rays propagated through the same HVA area as that for T4 and T3 (Figure 1). The duration of the source time function of T1 is basically short, i.e., ∼4 s that is determined using waveforms at other regional and teleseismic stations [ Kuge , 1994].…”