Abstract. Changes in stress in southern California are modeled from 1812 to 2025 using as input (1) stress drops associated with six large (7.0 < M < 7.5) to great (M > 7.5) earthquakes through 1995 and (2) stress buildup associated with major faults with slip rates > 3 mm/yr as constrained by geodetic, paleoseismic, and seismic measurements. Evolution of stress and the triggering of moderate to large earthquakes are treated in a tensoffal rather than a scalar manner. We present snapshots of the cumulative Coulomb failure function (ACFF) as a function of time for faults of various strike, dip, and rake throughout southern California. We take ACFF to be zero everywhere just prior to the great shock of 1812. We find that about 95% of those well-located M > 6 earthquakes whose mechanisms involve either strike-slip or reverse faulting are consistent with the Coulomb stress evolutionary model; that is, they occurred in areas of positive ACFF.
Space geodesy showed that broad-scale postseismic deformation occurred after the 1992 Landers earthquake. Three-dimensional modeling shows that afterslip can only explain one horizontal component of the postseismic deformation, whereas viscoelastic flow can explain the horizontal and near-vertical displacements. The viscosity of a weak, about 10-km-thick layer, in the lower crust beneath the rupture zone that controls the rebound is about 10(18) pascal seconds. The viscoelastic behavior of the lower crust may help to explain the extensional structures observed in the Basin and Range province and it may be used for the analysis of earthquake hazard.
A number of different Euler poles have been proposed by various authors during the past 20 years to describe the relative motion of Caribbean (CA) and North American (NA) plates. These different solutions are a consequence of the small number of focal mechanism solutions of earthquakes, the short length of the plate boundaries of the Caribbean that consists of an active spreading center, the complicated and multibranched fault systems of several parts of the plate boundaries, and biases introduced in using slip vectors along the Middle American Trench to close plate motion circuits in computing CA-NA Euler poles. Slip vectors from focal mechanisms are now the strongest constraints on the direction of current plate motion. We use 66 slip vectors derived from 117 focal mechanisms of shallow earthquakes located on or near the boundaries between the Caribbean and either the NA or South American (SA) plates to calculate a best fitting, present-day rotation pole for CA-NA. It is located at 68.4øN, 126.3øW, near Barrow, Alaska. In making this calculation, we effectively extended the length of the plate boundary considered in the calculation by using data from the CA-SA plate boundary and rotating them to the CA-NA reference frame using the Nuvel 1 pole for NA-SA motion and 20 mm/yr as the rate of CA-SA plate motion along the southeastern Caribbean. The result is not very sensitive to CA-SA rates. The azimuth of plate motion is about N70øE along most of the CA-NA boundary. For example, along the Puerto Rico Trench, several focal mechanisms indicate highly oblique motion with a small component of plate convergence along shallow, south dipping thrust faults. The highly oblique plate motion along the inner wall of the Puerto Rico Trench is indicative of strong coupling of that forearc with the Caribbean plate and of the potential of that zone to generate great earthquakes. Slip vectors are very consistent with one another in areas in which at least one of the interacting plates is oceanic. Focal mechanisms and the distribution of earthquakes exhibit greater scatter, however, in areas such as Hispaniola where continental or thick island arc lithosphere is being deformed and is present on both sides of that complex plate boundary. In addition, other mechanisms indicate northerly subduction of the Caribbean beneath southeastern Hispaniola along the western Muertos Trough, nom•al faulting to the east of the Lesser Antilles associated with the bending of the downgoing plate, and normal faulting or reverse faulting in more localized areas near the plate boundary. As part of the analysis, we also calculated Euler poles for CA-SA motion at 52øN, 81øW and Cocos-Caribbean (CO-CA) at 22øN, 120øW. These poles are consistent with recent models of transtensional development since about 10 m.y. ago along the plate boundary zone of the southeastern Caribbean and with CO-CA motion that involves subduction along the Middle America Trench as well as right-lateral, strikeslip faulting and extension along the volcanic zone of Central America. T...
Abstract. We calculate the evolution of stresses in southern California, extending the study of Deng and Sykes [1997] by increasing from 6 to 36 the number of earthquakes for which coseismic changes in stress are computed and by expanding from M > 6 to M > 1.8 the range of magnitudes M of events whose focal mechanism solutions are examined in the context of the evolving stress field. The cumulative stress on a given date is calculated with respect to an arbitrary zero baseline just before the 1812 Wrightwood earthquake. By taking into account the long-term stress loading associated with 98 fault segments and coseismic stress changes for 36 significant The fact that the locations of most moderate-, small-, and micro-size earthquakes are still related to stress changes remaining from large historical events might be used to constrain slip distribution of some of those earthquakes and to constrain the locations of future significant events.
Abstract.Following the M•o 6.7 Northridge earthquake, significant postseismic displacements were resolved with GPS. Using a three-dimensional viscoelastic model, we suggest that this deformation is mainly driven by viscous flow in the lower crust. Such flow can transfer stress to the upper crust and load the rupture zone of the main shock at a decaying rate. Most aftershocks within the rupture zone, especially those that occurred after the first several weeks of the main shock, may have been triggered by continuous stress loading from viscous flow. The long-term decay time of aftershocks (about 2 years) approximately matches the decay of viscoelastic loading, and thus is controlled by the viscosity of the lower crust. Our model provides a physical interpretation of the observed correlation between aftershock decay rate and surface heat flow.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.