Patricia Alvarado's Research Page
Crustal seismicity in the back-arc region of the Southern Central Andes from historic to modern timesThe Andean Cordillera is the result of the compression between the Nazca and South America tectonic plates. The convergence rate between the two plates of 85 mm/yr at an azimuth of 78° generates a large number of earthquakes. In the south-central Andes, four seismogenic zones are identified: the outer-rise region located in the subducting plate seaward from the trench, the plate interface, within the down-going slab, and within the overriding South America plate. While the largest magnitude earthquakes are the interplate subduction zone events, the historically most devastating earthquakes have been the moderate-to-large magnitude crustal earthquakes in the South American plate. |
|
The subducting slab under the South Central Andes exhibits some significant along-strike changes in
the subduction geometry. One of these changes occurs around 33°S where the Nazca slab subducts near
horizontally north of 33°S and inclines ~30° south of this latitude. The region above the flat
subduction is marked by a shutoff of the active volcanic arc, and has a wider back-arc region of
active deformation and earthquakes. My studies will focus on the crustal seismicity and crustal
structure in the back-arc region of the Sierras Pampeanas of Argentina above the flat slab. I m
studing crustal earthquakes using broadband seismic data collected during the Chile-Argentina
Geophysical Experiment (CHARGE) between November 2000 and May 2002. During that period, 75
crustal earthquakes with magnitudes greater than 4.0 occurred under the main cordillera and in the
backarc region. I obtained the moment tensor solutions and depths for as many of these
events as possible using a regional moment tensor inversion technique. |
|
For more details see: |
|
In addition to providing seismotectonic information, these continental earthquakes can also be
used to determine the crustal structure. Some geologic studies suggest that the Paleozoic terrane
sutures, some of them later reactivated during the Mesozoic extension, have an important
control on the present day Andean deformation. One of my goals is to study the crustal seismic
velocity structure by utilizing raypaths that sample different geologic provinces in the region.
With the available event-station paths, I will be able to compare crustal velocities
from the western and eastern Pampean ranges, as well as in the Cordillera and Precordillera.
The basement rocks exposed in the western Sierras Pampeanas are more mafic than the basement
exposed in the eastern Sierras Pampeanas. If this is representative of the entire crust,
then I should be able to map out these differences using crustal earthquake data. For more details see: |
|
The Sierras Pampeanas and Precordillera have a long history of devastating earthquakes in Argentina.
Within the past century, at least three crustal earthquakes with magnitudes larger than 7.0 have
caused approximately 5,000 deaths and major economic losses. Only the 1977 earthquake has been
studied in any detail. I will study these previous large events using historic seismograms recorded
at teleseismic distances, which will require collecting and digitizing historic paper seismograms,
and developing techniques to constrain their source parameters. Although a time-consuming process,
this will allow me to extend my study of the crustal seismicity from the present day to a 60-year-long
period. The longer period of time will be very important to evaluating the seismic hazards of
the region. For more details see: |
<< Back to Home Page |
|
Latest revision: January 9, 2005 |