## Wednesday, May 4, 2016

### Plotting historical moment tensors from GCMT directly

I created this script for our earthquake of this week (There are some other scripts for different purposes, I may add them sometime later, but you can find them at my Github). The purpose of this script is that, a lot of times, when we look at an earthquake occured recently, we want to see the historical moment tensors in this region. These historical moment tensors can tell us a lot of things, i.e. tectonic setting, fault information, etc. Then using this script, all you need do is to specify the starttime, endtime, and region (for region, right now, I just use one recent earthquake location as the center, and expand them both in latitude and longitude a certain degree).
For example, the 2016 M7.8 Ecuador, if we want to see the historical moment tensors in this region, we can do as the followings. You can find the script on Qingkai's Github.
In [1]:
import warnings
warnings.filterwarnings('ignore')
from obspy import UTCDateTime
import urllib
import urllib2
import numpy as np
from collections import OrderedDict
import matplotlib.pyplot as plt
from mpl_toolkits.basemap import Basemap
from obspy.imaging.beachball import beach
from matplotlib.lines import Line2D
from BeautifulSoup import BeautifulSoup
%pylab inline

Populating the interactive namespace from numpy and matplotlib

In [3]:
def get_hist_mt(t1, t2, llat = '-90', ulat = '90', llon = '-180', ulon = '180',
lmw = 0, umw = 10, evla = None, evlo = None, step = 2.0, list_ = '6'):
'''
Function to query the GCMT and save the data for ploting. If evla and
evlo are provided, it will use this location as the center and adding
step to both latitude and longitude for the box.

t1 - starttime, example: UTCDateTime("1979-01-01")
t2 - endtime, example: UTCDateTime("2016-01-01")
llat - lower latitude
ulat - upper latitude
llon - left longitude
ulon - right longitude
lmw - the minimum magnitude to search
umw - the maximum magnitude to search
evla - latitude of the current earthquake
evlo - longitude of the current earthquake
step - from current earthquake location, expand lat/lon for a box
list_ - format of data you want to return from the GCMT
'''

yr = t1.year
mo = t1.month
day = t1.day
oyr = t2.year
omo = t2.month
oday = t2.day
mat = {}
locs = locals()

base_url = 'http://www.globalcmt.org/cgi-bin/globalcmt-cgi-bin/CMT4/form'

#note here, we must use the ordered Dictionary, so that the order in the
#url is exactly the same order
param = OrderedDict()
param['itype'] = 'ymd'
param['yr'] = yr
param['mo'] = mo
param['day'] = day
param['otype'] = 'ymd'
param['oyr'] = oyr
param['omo'] = omo
param['oday'] = oday
param['jyr'] = '1976'
param['jday'] = '1'
param['ojyr'] = '1976'
param['ojday'] = '1'

param['nday'] = '1'
param['lmw'] = str(lmw)
param['umw'] = str(umw)
param['lms'] = '0'
param['ums'] = '10'
param['lmb'] = '0'
param['umb'] = '10'

# now specify the region box
if evla and evlo is not None:
llat = evla - step
ulat = evla + step
llon = evlo - step
ulon = evlo + step

# save parameter for query
param['llat'] = llat
param['ulat'] = ulat
param['llon'] = llon
param['ulon'] = ulon

param['lhd'] = '0'
param['uhd'] = '1000'
param['lts'] = '-9999'
param['uts'] = '9999'
param['lpe1'] = '0'
param['upe1'] = '90'
param['lpe2'] = '0'
param['upe2'] = '90'
param['list'] = list_

# build the URL
url = "?".join((base_url, urllib.urlencode(param)))
print url

# grab data and parse it
page = urllib2.urlopen(url)
parsed_html = BeautifulSoup(page)
mecs_str = parsed_html.findAll('pre')[1].text.split('\n')

# string to array
def convertString(mecs_str):
return map(float, mecs_str.split()[:9])

psmeca = np.array(map(convertString, mecs_str))

# save the results for plotting
mat['psmeca'] = psmeca
mat['url'] = url
mat['range'] = (llat, ulat, llon, ulon)
mat['evloc'] = (evla, evlo)
return mat

def plot_hist_mt(psmeca_dict, figsize = (16,24), mt_size = 10, \
pretty = False, resolution='l'):
'''
Plot the historical moment tensor from the query of GCMT

psmeca_dict - dictionary that returned from get_hist_mt function
figsize - tuple of the size of the figure
mt_size - size of the moment tensor on the plot
pretty - boolean, whether want to plot nice maps
resolution - low or high as you want
'''

if psmeca_dict['psmeca'] != []:
psmeca = psmeca_dict['psmeca']
#get the latitudes, longitudes, and the 6 independent component
lats = psmeca[:,1]
lons = psmeca[:,0]
focmecs = psmeca[:,3:9]
depths =  psmeca[:,2]
(llat, ulat, llon, ulon) = psmeca_dict['range']
evla = psmeca_dict['evloc'][0]
evlo = psmeca_dict['evloc'][1]

plt.figure(figsize=figsize)
m = Basemap(projection='cyl', lon_0=142.36929, lat_0=38.3215,
llcrnrlon=llon,llcrnrlat=llat,urcrnrlon=ulon,urcrnrlat=ulat,\
resolution=resolution)

m.drawcoastlines()
m.drawmapboundary()

if pretty:
m.etopo()
else:
m.fillcontinents()

llat = float(llat)
ulat = float(ulat)
llon = float(llon)
ulon = float(ulon)

m.drawparallels(np.arange(llat, ulat, (ulat - llat) / 4.0), \
labels=[1,0,0,0])
m.drawmeridians(np.arange(llon, ulon, (ulon - llon) / 4.0), \
labels=[0,0,0,1])

ax = plt.gca()
x, y = m(lons, lats)

for i in range(len(focmecs)):

if depths[i] <= 50:
color = '#FFA500'
#label_
elif depths[i] > 50 and depths [i] <= 100:
color = 'g'
elif depths[i] > 100 and depths [i] <= 200:
color = 'b'
else:
color = 'r'

index = np.where(focmecs[i] == 0)[0]

#note here, if the mrr is zero, then you will have an error
#so, change this to a very small number
if focmecs[i][0] == 0:
focmecs[i][0] = 0.001

try:
b = beach(focmecs[i], xy=(x[i], y[i]),width=mt_size, \
linewidth=1, facecolor=color)
except:
pass

b.set_zorder(10)

x_0, y_0 = m(evlo, evla)
m.plot(x_0, y_0, 'r*', markersize=25, zorder = 10)

circ1 = Line2D([0], [0], linestyle="none", \
marker="o", alpha=0.6, markersize=10, markerfacecolor="#FFA500")
circ2 = Line2D([0], [0], linestyle="none", \
marker="o", alpha=0.6, markersize=10, markerfacecolor="g")
circ3 = Line2D([0], [0], linestyle="none", \
marker="o", alpha=0.6, markersize=10, markerfacecolor="b")
circ4 = Line2D([0], [0], linestyle="none", \
marker="o", alpha=0.6, markersize=10, markerfacecolor="r")
plt.legend((circ1, circ2, circ3, circ4), \
("depth $\leq$ 50 km", "50 km $<$ depth $\leq$ 100 km", \
"100 km $<$ depth $\leq$ 200 km", "200 km $<$ depth"), \
numpoints=1, loc=3)
plt.show()
else:
print 'No historical MT found!'

In [6]:
t1 = UTCDateTime("1979-01-01")
t2 = UTCDateTime("2016-01-01")

psmeca = get_hist_mt(t1, t2, evla = 0.371, evlo= -79.940, step = 8, lmw = 0)
plot_hist_mt(psmeca, figsize = (12, 10),  mt_size = 0.4, pretty = True, resolution='l')






#### 1 comment:

1. ok thanks for this post it's quite informative and I have learned new things.
runkeeper