GPS crustal strain, postglacial rebound, and seismic hazard in eastern North America: The Saint Lawrence valley example

Abstract

We present Global Positioning System (GPS) measurements that constrain the amplitude, pattern, and origin of crustal deformation in the Saint Lawrence valley, Québec, one of the most seismically active regions of eastern North America. The GPS network shows coherent southeastward motion of 0.6 ± 0.2 mm yr−1, relative to North America, and uplift of 2.6 ± 0.4 mm yr−1. Network average horizontal strain rates are mostly ESE‐WNW shortening at (1.7 ± 1.0) × 10−9 yr−1. The shortening rate across the Charlevoix seismic zone is about twice as big as the regional average. These measurements are consistent with both postglacial rebound (PGR) models and the deformation style indicated by earthquake focal mechanisms. Although the GPS data do not discriminate between various models of crustal deformation, they provide important constraints on large earthquake recurrence. Assuming that the GPS strain estimates are representative of seismic moment release, they constrain the maximum magnitude of truncated Gutenberg‐Richter recurrence statistics in the Charlevoix seismic zone to MX = 7.8 ± 0.6 (one M ≥ 7 earthquake per 400–1300 years). The remarkable agreement between the GPS strain rates, seismic catalogue statistics, and PGR predictions suggests that in Charlevoix, most of the PGR‐driven crustal strain may be released by large (M ≥ 7) earthquakes. In the rest of the Saint Lawrence valley, PGR strain rates are significantly larger than seismic strain rates, suggesting either that PGR deformation remains mostly elastic or that large events are more frequent than indicated by small earthquake statistics (i.e., characteristic earthquakes).

Identification of Glacial Isostatic Adjustment in Eastern Canada Using S Transform Filtering of GPS Observations

“…It can be seen that almost 90% of the velocity vectors above a latitude of 44°N are directed up and most of the vectors below 44°N latitude are directed down. This velocity map is in accordance with other GIA observations for Canada (MAZZOTTI et al, 2005). There is a clear indication of a hinge line around 44°N that runs approximately parallel to the Saint Lawrence River in the east (PELTIER, 2002;TUSHINGHAM and PELTIER, 1991), where the lithosphere above the hinge line shows uplift and those portions below the hinge line show subsidence.…”

“…Figure 8 depicts the horizontal velocity map for the region (resultant velocity of the north-south and the east-west velocities). The horizontal velocity pattern is difficult to interpret, in part due to the short time periods for a significant number of the available stations (SELLA et al, 2007;MAZZOTTI et al, 2005;PELTIER and DRUMMOND, 2008).…”

Statistical significance of trends in Zenith Wet Delay from re-processed GPS solutions

“…An uncertainty of trend estimates for ZWD data can be used for climate applications only if the stochastic character, which is not a white noise model, is fully accounted for. An alternative would be to follow the approach presented by Mazzotti et al (2005) for the position time series. Take the uncertainties of ZWD trends estimated with WN process and multiply them by 8 to estimate the approximate uncertainty that the ZWD trend would have if computed with AR(1) + WN processes.…”

GeoStrain: An open source software for calculating crustal strain rates

“…This simplification is justified by the very low vertical velocity gradients compared to the horizontal velocities. However, this is not the case for the intraplate regions such as the Saint Lawrence valley, eastern Canada, in which the vertical velocities can be 5-10 times larger than the differential horizontal velocities (Mazzotti et al, 2005). In such a case, Malvern (1969) considers the vertical velocities and proposes a complete formulation to calculate the horizontal strain rate tensors as: is the position vector of the measuring stations in the local geodetic system, and r is earth's radius.…”

“…Haines et al (1998), Kreemer et al (2000), and Beavan and Haines (2001), among others, have used point displacement observations of geodetic networks and strain evaluated by geologic and geophysical information such as earthquake focal mechanisms to invert for the Euler pole that locally minimizes the strain rate and velocity field residuals along a regional curvilinear reference system. Mazzotti et al (2005) decomposed the velocity field into three components including a uniform horizontal strain rate, a translation (horizontal and vertical), and a horizontal rigid rotation. Then, they adjusted this seven-parameter model to the GPS velocities at the measuring points.…”