Anna Kaiser

Rapid Earthquake Characterization Using MEMS Accelerometers and Volunteer Hosts Following the M 7.2 Darfield, New Zealand, Earthquake

We test the feasibility of rapidly detecting and characterizing earthquakes with the Quake-Catcher Network (QCN) that connects low-cost microelectromechan- ical systems accelerometers to a network of volunteer-owned, Internet-connected com- puters. Following the 3 September 2010 M 7.2 Darfield, New Zealand, earthquake we installed over 180 QCN sensors in the Christchurch region to record the aftershock se- quence. The sensors are monitored continuously by the host computer and send trigger reports to the central server. The central server correlates incoming triggers to detect when an earthquake has occurred. The location and magnitude are then rapidly esti- mated from a minimal set of received ground-motion parameters. Full seismic time series are typically not retrieved for tens of minutes or even hours after an event. We benchmark the QCN real-time detection performance against the GNS Science GeoNet earthquake catalog. Under normal network operations, QCN detects and characterizes earthquakeswithin9.1softheearthquakeruptureanddeterminesthemagnitudewithin 1 magnitude unit of that reported in the GNS catalog for 90% of the detections.

Strong shaking in recent New Zealand earthquakes

On 4 September 2010 a surface-rupturing crustal earthquake (Mw 7.1) struck the Canterbury Plains region of New Zealands South Island [Gledhill et al., 2011]. The Canterbury Plains is a region of relatively low seismicity in New Zealand, and the structure that ruptured was a previously unmapped fault (Figure 1a). Fortunately, even though parts of the region experienced liquefaction of unconsolidated sediments and sands—including neighborhoods of the city of Christchurch (population 377,000)—no fatalities occurred. Compared to the average New Zealand aftershock decay model, the aftershock sequence for the 2010 earthquake was relatively underproductive for the first 5 months. But on 22 February 2011 anMw 6.2 aftershock (teleseismic and regional estimates range from (Mw 6.1 to (Mw 6.3 with regional inversions favoring higher values) occurred within kilometers of the center of Christchurch (A. E. Kaiser et al., The (Mw 6.2 Christchurch earthquake of February 2011: Preliminary report, submitted to New Zealand Journal of Geology and Geophysics, 2011). The event increased the productivity of other aftershocks (Figure 1b). This particular aftershock was devastating, generating much more destruction than theMw 7.1 event, including more than 180 fatalities. Recorded peak ground acceleration (PGA) in the city was more than double the acceleration of gravity (g). Many of the poorly consolidated, low-shear-wave-velocity soils liquefied during the shaking. Damage estimates reached approximately US

The 2016 Kaikōura, New Zealand, Earthquake: Preliminary Seismological Report

15 billion, making the aftershock New Zealands costliest natural disaster.