Also, the aftershocks have already slowed considerably. Taken together, the 6,000 aftershocks still account for only 10 percent of the energy released during the sequence, while the mainshock accounts for 90 percent. We cannot say when it will end, but we can say that the aftershocks have already grown far less frequent.Ī little perspective: While aftershocks can cause a great deal of anxiety for many, they are nothing compared to the mainshock in terms of destructive power. We are not surprised that strong aftershocks are still happening, and they do not suggest that a larger earthquake is on its way. Below, we will try to answer them as plainly and non-technically as possible.įirst, the short version: There is nothing unusual about this aftershock sequence. 30, and grew more insistent after the magnitude 5 aftershock on New Year's Eve. All of those questions popped up again Friday after the magnitude 4.9 aftershock, which was the largest since the night of Nov. 30 Anchorage earthquake, we’ve fielded far more questions about the aftershock sequence than we have about the magnitude 7.1 mainshock that started them. The article, "Consecutive Ruptures on a Complex Conjugate Fault System During the 2018 Gulf of Alaska Earthquake," was published in Scientific Reports at DOI: 10.Since the Nov. This method represents a promising step forward in modeling earthquake rupture processes in complex fault systems based only on seismic body waves, which may improve modeling of seismic wave propagation and mapping of complex fault networks in tectonically active areas. "Our findings show that irregular rupture stagnation 20 kilometers north of the earthquake's epicenter may have been promoted by a fault step across the seafloor fracture zone," explains co-author Assistant Professor Ryo Okuwaki, "They also indicate a causal link between rupture evolution and pre-existing bathymetric features in the Gulf of Alaska." These features caused discontinuities in the fault geometry that led to irregular rupture behavior. "Our model further suggests that this rupture tended to occur along weak zones in the sea floor: fracture zones that extend east-west, as well as plate-bending faults that run parallel to north-south-oriented magnetic lineaments." "Our results confirm previous reports that this earthquake ruptured a conjugate fault system in a multi-shock sequence," says study first author Shinji Yamashita. The main rupture stage of the earthquake, which lasted for 27 seconds, affected fault segments oriented both north-south and east-west. This approach allows us to analyze seismic P waves and estimate the focal mechanisms and rupture evolution of geometrically complex earthquakes involving rupture of multiple fault segments."īased on the distribution of aftershocks within one week of the main shock of the Gulf of Alaska earthquake, this method was applied to represent slip along a horizontal plane at a depth of 33.6 km. They then applied this method to the magnitude 7.9 earthquake that struck the Gulf of Alaska near Kodiak Island on January 23, 2018.Īs study co-author Professor Yuji Yagi explains, "Our method uses a flexible finite-fault inversion framework with improved smoothness constraints. In a new study published in Scientific Reports, a research team led by the University of Tsukuba developed a new method to model the details of complex earthquake rupture processes affecting systems of multiple faults. Of course, given the complexity of the environments where these ruptures typically occur, the reality is often much more complicated. Tsukuba, Japan - An earthquake is generally viewed to be caused by a rupture along a fault that is transmitted outward from its point of origin in a uniform, predictable pattern. The dashed rectangles highlight the rupture events recognised by this study. Lower-right panel shows the spatiotemporal distribution of the slip migration, projected along the north-south direction. Blue lines are our estimate of the faults, along with the fault movements indicated as arrows. Lower-left panel show the enlarged map of our result. Upper panels summarise the regional map of the study area, showing plate boundary (dashed line), seafloor fracture zones (solid lines), the epicentre (star) of the 2018 Gulf of Alaska earthquake and the aftershocks (dots).
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