Bulk, shear and scattering attenuation beneath Hawaiian Volcanos and in the oceanic crust extending to the Aloha Cabled Observatory

SUMMARY Seismic attenuation is measured from a swarm of 50 earthquakes in Kīlauea volcano in 2018, associated with caldera collapse. The traverse extends at nearly constant azimuth to the saddle between Mauna Loa and Mauna Kea, continuing to Maui beneath the distal flanks of three dormant volcanos. From Maui the traverse then extends seaward to the Aloha Cabled Observatory (ACO) on the seafloor north of O‘ahu. The effective attenuation is measured with respect to an ${\omega ^{ - 2}}$ earthquake source model. Frequency dependent ${Q_P}$ and ${Q_S}$ are derived. The initial path is shallow and uphill, the path to Maui propagates at mid-crustal depths, and the path to ACO extends through oceanic crust. The observations of ${Q_P} \le {Q_S}$ over each traverse are modelled as bulk attenuation ${Q_K}$. Several attenuation processes are observed, including ${Q_\mu }$, ${Q_K}$, $Q\sim f$, constant Q and scattering. The observation of bulk attenuation is ascribed to contrasting physical properties between basalt and water saturated vesicles. The ratio of Q values between shallow and mid-crustal propagation is used to derive an activation energy E* for the undetermined shear attenuation mechanism. A Debye relaxation peak is fit to the ${Q_S}( f )$ and ${Q_K}( f )$ observed for the mid-crustal pathway. A prior high-frequency attenuation study near Wake Island compares well with this Hawaiian Q data set, which in general shows lower values of Q than observed for Wake.

The Mw7.8 2016 Kaikōura earthquake

We provide a summary of the surface fault ruptures produced by the Mw7.8 14 November 2016 Kaikōura earthquake, including examples of damage to engineered structures, transportation networks and farming infrastructure produced by direct fault surface rupture displacement. We also provide an overview of the earthquake in the context of the earthquake source model and estimated ground motions from the current (2010) version of the National Seismic Hazard Model (NSHM) for New Zealand. A total of 21 faults ruptured along a c.180 km long zone during the earthquake, including some that were unknown prior to the event. The 2010 version of the NSHM had considered multi-fault ruptures in the Kaikōura area, but not to the degree observed in the earthquake. The number of faults involved a combination of known and unknown faults, a mix of complete and partial ruptures of the known faults, and the non-involvement of a major fault within the rupture zone (i.e. the Hope Fault) makes this rupture an unusually complex event by world standards. However, the strong ground motions of the earthquake are consistent with the high hazard of the Kaikōura area shown in maps produced from the NSHM.

Comparison of Near-Fault Effect Considered in Seismic Design Codes for Building

This paper compares the provisions of near-fault effect factors considered in the representative design codes in the world. It is found that the different codes carry out different near-fault effect values. Chinese, American, and New Zealand seismic design codes clearly present the near-fault effect factors, and Chinese seismic design code relatively presents the smallest near-fault effect values among the three codes. While Japanese code accounts for near-fault effect using empirical method and strong motion evaluation employing earthquake source model. The consideration of the near-fault effects in European Standard is the simplest among the five codes.

GENERATION OF SYNTHETIC ACCELEROGRAMS USING ENGINEERING EARTHQUAKE SOURCE MODEL

The strong motion records available during an earthquake can be treated as the response of the earth as a structural system to unknown forces acting at unknown locations. Thus, if the part of the earth participating in ground motion is modeled as a known finite elastic medium, one can model the source location and forces generated during the earthquake as an inverse problem. Based on this analogy, a simple model for the earthquake source is proposed, by assuming the source to be a sequence of impulses acting at locations yet to be found. These impulses and their locations are found using the normal mode expansion along with a minimization of mean squared error. The medium is assumed to be finite, elastic, homogeneous, layered and horizontal with specified boundary conditions. Detailed results are obtained for the Uttarkashi earthquake of 20th October 1991, in India. The impulse locations are shown to be closely associated with the underlying fault mechanism. The proposed model is then used to simulate the acceleration time histories at a few recording stations. The earthquake source expressed in terms of a sequence of impulses acting at different locations is applied to a 2D finite elastic medium. The acceleration time histories found from this model agree well with with the accelerations recorded for the earthquake.