Seismology and Isostasy#

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Downloads from the Internet#

We will need some files from the internet that will be used in this assignment. If you get errors in the following cell block, it probably means the machine (or the node in a cluster) you are calling this command from does not have direct internet access.

Note: If you are on the Adroit cluster in Princeton, please make sure you are within a Jupyter on Adroit Vis session since this node has internet access. You can use any other session for the remaining cells in this notebook; Jupyter for classes is suggested since a dedicated class environment (GEO203) with all necessary modules has been created for this course.

import os
import requests
from pathlib import Path

# Define the list of remote files to retrieve\n",
remote_urls = ['https://portal.globalseismology.org/files/DATA/GLOBALTOPO/ETOPO1_Ice_g_gmt4.grd']
path = '../PS_Plate_Tectonics/Files/'

# loop through all remote URL and download the files
for remote_url in remote_urls:
    # Define the local filename to save data
    # get the trailing filename after the last / of the path
    local_file = path + os.path.basename(remote_url)
    
    if not Path(local_file).is_file():
        # mke the directory if it does not exist
        if not os.path.isdir(path): os.makedirs(path)
    
        # Download remote and save locally
        r = requests.get(remote_url, allow_redirects=True)
        open(local_file, 'wb').write(r.content)

Part I: Mountain building and isostasy#

Mountain ranges are created at present subduction zones (for the Andes or the Himalayas) or past subduction zones (for the Appalachians). These are regions where the lithosphere is thickening due to the compressional stress, crustal thickening and volcanism, facilitated by the relatively lower strength of the lower crust (i.e. think of strength envelopes of continental crust).

../_images/Subduction_Zone.gif

Figure: Anatomy of a subduction zone setting. Source: USGS

In the schematic above, note that the continental crust at the mountain belt is thickened not only upward but also downward into the mantle asthenosphere. Mountain building causes relief, the elevation difference between peaks and adjoining areas which may already be above sea level.

import os
os.environ['PROJ_LIB'] = os.path.join(os.environ['CONDA_PREFIX'],'share/proj') # This is required for Basemap plotting to work

from mpl_toolkits.basemap import Basemap
import numpy as np
import matplotlib.pyplot as plt

fig = plt.figure(figsize=[14, 7])
# lon_0 is central longitude of projection.
# resolution = 'c' means use crude resolution coastlines.
m = Basemap(projection='robin',lon_0=0,resolution='c')
m.drawcoastlines()
# draw parallels and meridians.
m.drawparallels(np.arange(-90.,90.,30.))
m.drawmeridians(np.arange(-180.,180.,60.))
m.drawmapboundary()
m.etopo()
plt.title("Earth's Topography and Bathymetry",fontsize=20)
plt.show()
Clipping input data to the valid range for imshow with RGB data ([0..1] for floats or [0..255] for integers).
../_images/Seismology_Isostasy_4_1.png

Let us first explore surface topography from the [ETOPO1 model] and focus on the Andes mountain range in South America. We will make a cross-section that cuts through the mountain range so that we may calculate the local refief.

import xarray as xr
import numpy as np
import matplotlib.pyplot as plt
import plotly
plotly.offline.init_notebook_mode()