Preliminary Results From the November 25, 1988 Saguenay (QUEBEC) Earthquake

Abstract

The November 25, 1988 Saguenay, Québec earthquake (mb 5.9) was preceded by a foreshock 62 hours earlier (mb 4.4) and followed by over 50 aftershocks, of which only two have been larger than magnitude 3. The unusually large 29 km depth of the main shock is well determined using a field network deployed after the foreshock. Nearly all of the aftershock activity is shallower than the main shock, suggesting that the rupture propagated upwards. The event produced unexpectedly large amounts of high frequency energy, as evidenced by the value of mbLg (6.5) and by high accelerations observed at distances ranging from 40 to 800 km. Focal mechanisms for the foreshock, main shock and largest aftershock indicate thrust faulting. The felt area exceeds 3.5 million km2 and closely approaches that of the 1925 Charlevoix earthquake. The location of the Saguenay event in a region with little historic seismicity, its depth, and its large high-frequency generation, pose several problems for existing models of seismic zoning and hazard assessment for Eastern North America.

Earthquake-triggered submarine landslides in the St. Lawrence Estuary (Québec, Canada) during the last two millennia and the record of the major 1663 CE M ≥7 event

“…In addition to the 1663 CE earthquake, four earthquakes with M 5.9 to 6.6 occurred in the CKSZ in 1860, 1870, 1925and 1988CE (Smith, 1962Lamontagne et al, 2003;Lamontagne et al, 2018) (Fig. 1).…”

Modified frequency-wavenumber algorithm for regional seismograms using Filon's quadrature: modelling ofLgwaves in eastern North America

“…The weak motions are recorded on the short-period Eastern Canadian Telemetered Network (ECTN, Fig. 1) stations at distances from 300 to 700 km (North et al 1989). In this study, we used seismograms from eight stations: SBQ, GRQ, KLN, WBO, GGN, CKO, LMN and EEO.…”

Modeling Regional Seismic Waves

“…The HRV recording of the Saguenay earthquake, at an epicentral distance of 825 kin, Is one of the first such unclipped recordings of a sizable earthquake occurring in a predominantly shield region. This event is the largest earthquake to occur in over 50 years in Eastern North America and was recorded both loca!ly and teleseismically ( e. g. North et al, 1989;and Somerville et al, 1989 ). These studies provide seismic source parameters for the event ( strike -323', dip 65, rake -78#, moment ,5.0X10 2 4 dyne-cm, depth -28 kin ), as well as some constraints on the time history.…”

“…Thus far, we have assumed that the earthquake source parameters were well determined by other studies, namely that the strike, dip and rake angles are roughly 323", 65" and 78' respectively. The source depth was estimated by regional P., and telesesmic depth phases to be near 28 km ( Somerville et a., 1989;North et al, 1989 ). The source time history is not so well known nor are the rupture properties.…”