We present a new global model of plate motions and strain rates in plate boundary zones constrained by horizontal geodetic velocities. This Global Strain Rate Model (GSRM v.2.1) is a vast improvement over its predecessor both in terms of amount of data input as in an increase in spatial model resolution by factor of ∼2.5 in areas with dense data coverage. We determined 6739 velocities from time series of (mostly) continuous GPS measurements; i.e., by far the largest global velocity solution to date. We transformed 15,772 velocities from 233 (mostly) published studies onto our core solution to obtain 22,511 velocities in the same reference frame. Care is taken to not use velocities from stations (or time periods) that are affected by transient phenomena; i.e., this data set consists of velocities best representing the interseismic plate velocity. About 14% of the Earth is allowed to deform in 145,086 deforming grid cells (0.25° longitude by 0.2° latitude in dimension). The remainder of the Earth's surface is modeled as rigid spherical caps representing 50 tectonic plates. For 36 plates we present new GPS-derived angular velocities. For all the plates that can be compared with the most recent geologic plate motion model, we find that the difference in angular velocity is significant. The rigid-body rotations are used as boundary conditions in the strain rate calculations. The strain rate field is modeled using the Haines and Holt method, which uses splines to obtain an self-consistent interpolated velocity gradient tensor field, from which strain rates, vorticity rates, and expected velocities are derived. We also present expected faulting orientations in areas with significant vorticity, and update the no-net rotation reference frame associated with our global velocity gradient field. Finally, we present a global map of recurrence times for Mw=7.5 characteristic earthquakes.

A geodetic plate motion and Global Strain Rate Model

[1] It has been known for a long time that slip accompanying earthquakes accounts for only a fraction of plate tectonic displacements. However, only recently has a fuller spectrum of strain release processes, including normal, slow, and silent earthquakes (or slow slip events) and continuous and episodic slip, been observed and generated by numerical simulations of the earthquake cycle. Despite a profusion of observations and modeling studies the physical mechanism of slow slip events remains elusive. The concurrence of seismic tremor with slow slip episodes in Cascadia and southwestern Japan provides insight into the process of slow slip. A perceived similarity between subduction zone and volcanic tremor has led to suggestions that slow slip involves fluid migration on or near the plate interface. Alternatively, evidence is accumulating to support the notion that tremor results from shear failure during slow slip. Global observations of the location, spatial extent, magnitude, duration, slip rate, and periodicity of these aseismic slip transients indicate significant variation that may be exploited to better understand their generation. Most slow slip events occur just downdip of the seismogenic zone, consistent with rate- and state-dependent frictional modeling that requires unstable to stable transitional properties for slow slip generation. At a few convergent margins the occurrence of slow slip events within the seismogenic zone makes it highly likely that transitions in frictional properties exist there and are the loci of slow slip nucleation. Slow slip events perturb the surrounding stress field and may either increase or relieve stress on a fault, bringing it closer to or farther from earthquake failure, respectively. This paper presents a review of slow slip events and related seismic tremor observed at plate boundaries worldwide, with a focus on circum-Pacific subduction zones. Trends in global observations of slow slip events suggest that (1) slow slip is a common phenomena observed at almost all subduction zones with instrumentation capable of recording it, (2) different frictional properties likely control fast versus slow slip, (3) the depth range of slow slip may be related to the thermal properties of the plate interface, and (4) the equivalent seismic moment of slow slip events is proportional to their duration (Moατ), different from the Moατ3 scaling observed for earthquakes.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2006RG000208

Slow slip events and seismic tremor at circum-Pacific subduction zones

Wide plate margin deformation, southern Central America and northwestern South America, CASA GPS observations

Linear Differential Operators By Prof. Cornelius Lanczos. Pp. xvi + 564. (London: D. Van Nostrand Co., Ltd.; New York: D. Van Nostrand Company, Inc., 1961.) 80s.

Linear Differential Operators

Velocities from 153 continuously-operatingGPS sites on the Caribbean, North American, and Pacic plates arecombinedwith61newlyestimatedPacic-Cocosseafloor spreading rates and additional marine geophysical data to deriveanewestimate of present-dayCocos-Caribbean plate motion. AcomparisonofthepredictedCocos-Caribbean di- rectiontoslipdirectionsofnumerousshallow-thrustsubduc- tion earthquakes from the Middle America trench between Costa Rica and Guatemala shows the slip directions to be deflected 10 clockwise from the plate convergence direc- tion, supporting thehypothesisthatfrequentdextralstrike- slip earthquakes along the Central American volcanic arc result from partitioning of oblique Cocos-Caribbean plate convergence. Linear velocity analysis for forearc locations in Nicaragua and Guatemala predicts 14 2m m yr 1 of northwestward trench-parallel slip of the forearc relative to theCaribbean plate, possibly decreasing inmagnitude inEl Salvador and Guatemala, where extension east of the vol- canic arc complicates the tectonic setting.

/pdf/a-new-estimate-for-present-day-cocos-caribbean-plate-motion-2etuxhy7i5.pdf

A new estimate for present-day Cocos-Caribbean Plate motion: Implications for slip along the Central American Volcanic Arc

Global Positioning System (GPS) observations in Costa Rica from 1994 to 1997 reveal a complex pattern of motion consistent with the superposition of seismic cycle and secular plate margin deformation. In the south, velocity vectors are consistent with motion of the Panama Block plus postseismic deformation following the 1991 Limon earthquake and interseismic strain due to partial locking of the Middle America Trench (MAT) thrust. In the northwest, sites west of the volcanic arc are moving to the NW as a forearc sliver. Superimposed on this sliver motion are vertical and horizontal interseismic deformations from the adjacent Nicoya segment of the MAT. We apply two different inverse methods to understand the source of the seismic strain in NW Costa Rica. We compare fault-locking models derived using a singular value decomposition inversion with that of a simulated annealing global optimization approach. Both methods yield similar models for partial locking of the thrust interface beneath the Nicoya Peninsula. Our results define an area of nearly fully locked fault beneath the outer coast of the southern portion of the peninsula, with somewhat lower coupling beneath the northern half and with low coupling elsewhere. These initial results show the promise for detailed imaging of the locked portion of a thrust interface responsible for future large subduction zone earthquakes.

Seismic cycle and plate margin deformation in Costa Rica: GPS observations from 1994 to 1997

https://www.cpp.edu/~marshall/costa_rica_reading/Iinuma_04_Nicoya_GPS.pdf

E. Hernandez

Papers

Seismic cycle and plate margin deformation in Costa Rica: GPS observations from 1994 to 1997

Inter-plate coupling in the Nicoya Peninsula, Costa Rica, as deduced from a trans-peninsula GPS experiment

Vent , Voluminous Lava Emissions, Steep Slopes and Pyroclastic Flows at Arenal Volcano, Costa Rica