Development of magnitude-bound relations for paleoliquefaction analyses: New Zealand case study

Abstract

a b s t r a c tMagnitude-bound relations are often used to estimate paleoearthquake magnitudes from paleoliquefaction data. This study proposes New Zealand-based magnitude-bound curves that are developed using (a) liquefaction field observations and (b) a newly proposed back-calculation approach that combines the simplified liquefaction evaluation procedure with a regionally appropriate ground motion prediction equation. For (b) both deterministic and probabilistic frameworks are proposed. The magnitude bound curves back-calculated using either the deterministic or probabilistic frameworks are advantageous in that they can be used to predict the spatial distribution of liquefaction in regions where historical liquefaction field observations are limited or poorly documented, and because soil-and site-specific conditions can be incorporated into magnitude-bound analyses. Moreover, curves developed using the probabilistic framework allow for the range of possible causative earthquake magnitudes to be better understood and quantified. To demonstrate the use of the proposed relations, paleoliquefaction features discovered in eastern Christchurch (NZ) are analyzed. The 1869~M w 4.8 Christchurch earthquake and/or 1717~M w 8.1 Alpine Fault earthquake are found to be the most likely candidates amongst known historical and paleoearthquakes for triggering liquefaction over the permissible time range (ca. 1660 to 1905 A.D.). This study demonstrates the potential of the proposed magnitude-bound curves to provide insight in to past, present, and future hazards, proving their utility even in cases of limited evidence. The approach of developing and applying magnitude bound curves proposed herein is not limited to parts of New Zealand, but rather, can be applied worldwide.

Liquefaction Features Produced by the 2010–2011 Canterbury Earthquake Sequence in Southwest Christchurch, New Zealand, and Preliminary Assessment of Paleoliquefaction Features

“…These results suggest high probabilities (16%-93% and 31%, respectively) that sources within a 60 km radius of Lincoln as well as the much more distant (135 km) Alpine fault can produce extensive liquefaction. Maurer et al (2015) show similar results for a site in eastern Christchurch.…”

“…As a first approximation to excluding some of these seismic-source candidates, we used a PGA 7:5 threshold approach (e.g., Quigley et al, 2013;Santucci de Magistris et al, 2013) and the new magnitude-bound relations developed from historic New Zealand liquefaction data (Maurer et al, 2015). For the PGA 7:5 threshold approach, we used two different ground-motion prediction equations (GMPEs, McVerry et al, 2006;Bradley, 2013) to calculate the PGA 7:5 (magnitude weighted; Youd et al, 2001) at our site from modeled ruptures of each fault (Table 1).…”

“…The probabilities of liquefaction at Lincoln for various seismic sources based on the magnitude-bound relations developed by Maurer et al (2015) are shown in Table 1. These results suggest high probabilities (16%-93% and 31%, respectively) that sources within a 60 km radius of Lincoln as well as the much more distant (135 km) Alpine fault can produce extensive liquefaction.…”

“…However, given that there is a rich set of recorded PGA data close to our site, we consider that using this approach in conjunction with Maurer et al (2015) may bring some more insights into what earthquake sources could have produced paleoliquefaction at Lincoln. To assess the threshold PGA 7:5 at which liquefaction may occur at our study site, we used the Canterbury records at the nearby LINC seismic station (∼3 km away from the site), which is located on similar soil (type D soil of the New Zealand Standard NZS1170, 2004), and information on historic earthquakes.…”

“…Figure 14 and Table 1 can also help to assess this question. We calculated the possible PGA 7:5 and the probabilities of liquefaction (from Maurer et al, 2015) for these two events using the mean distance and M w values (there is great uncertainty in these two parameters). Our calculations suggest that it is highly likely that the 1870 Lake Ellesmere event produced liquefaction at Lincoln.…”