H/V Microtremor Response

The Meinong earthquake registered a magnitude of Mw 6.3 (ML6.4) with a focal depth of 16.7 km by Taiwan Central Weather Bureau (CWB) and 23 km by USGS. The focal mechanism to the main event was characterized as strike-slip with an oblique thrust component. Seven aftershocks were recorded within the 24-hour window after the main shock with all of the aftershocks occurring west of the mainshock and with much deeper focal depths.
No significant damage was reported in the epicentral region. However, damage was reported about 30 km (25 miles) west of the epicenter in Tainan City where more than 20 multi-story buildings constructed under relatively modern building codes were severely damaged, including seven that suffered a complete collapse. There were some unexpected structural performances, geographical damage patterns, and liquefaction manifestation from the Meinong earthquake compared with prior earthquakes of similar magnitude.
The Geotechnical Extreme Events Reconnaissance (GEER) team brought two sets of seismometers to Tainan and conducted horizontal-to-vertical (H/V) spectral ratio of microtremor measurements (Nakamura’s technique, referred to as H/V measurements here after) at 10 sites where structure, foundation, or slope damage from the Meinong earthquake was observed.