Ground Motion Characteristics of the 2015 Gorkha, Nepal, Earthquake and Its Effects on a Prototype Unreinforced Masonry Building

The 7.8-magnitude Nepal earthquake on April 25, 2015, caused more than 9,000 fatalities and tremendous damage to civil infrastructures. Some unique characteristics of this earthquake and its effects on a prototype unreinforced masonry (URM) building have been investigated in this paper. The ground motion has short period components in the period range of T < 0.5 s as well as long-period components in the period range of 4-6 s. This characteristic is unique with respect to recorded ground motions in other parts of the world and with respect to the design response spectra in the Kathmandu region. Effects of this particular composition of frequency contents are discussed within the context of both elastic and inelastic response spectra. Common ground motion parameters for this earthquake have been investigated to compare the destructiveness of this earthquake to other historical earthquakes. In addition to this, acceleration spectrum intensity (ASI), which has been typically utilized for seismic evaluation of concrete dams, has been investigated to show unique characteristics of this earthquake. The long-period motion in the recorded time histories can be approximated by an analytical pulse model available in the literature. Frequency contents of this earthquake have also been investigated by using the empirical mode decomposition (EMD) approach, which provides insight into the contributions of various frequency contents to the recorded ground motion. It is also demonstrated that, although the record motion has a long predominant period, it is capable of severely damaging stiff, short-period, unreinforced masonry structures with timber diaphragm because of the presence of short-period components in the ground motion.