def RGF_from_SW4(path_to_green=".",
t0=0,
file_name=None,
origin_time=None,
event_lat=None,
event_lon=None,
depth=None,
station_name=None,
station_lat=None,
station_lon=None,
output_directory="sw4out"):
"""
Function to convert reciprocal Green's functions from SW4 to tensor format
Reads the reciprocal Green's functions (displacement/unit force) from SW4 and
performs the summation to get the Green's function tensor.
RGFs from SW4 are oriented north, east and positive down by setting az=0.
Assumes the following file structure:
f[x,y,z]/station_name/event_name.[x,y,z]
"""
import os
from obspy.core import read, Stream
from obspy.geodetics.base import gps2dist_azimuth
from obspy.core.util.attribdict import AttribDict
# Defined variables (do not change)
dirs = ["fz", "fx", "fy"] # directory to displacement per unit force
du = [
"duxdx", "duydy", "duzdz", "duydx", "duxdy", "duzdx", "duxdz", "duzdy",
"duydz"
]
orientation = ["Z", "N", "E"] # set az=0 in SW4 so x=north, y=east
cmpaz = [0, 0, 90]
cmpinc = [0, 90, 90]
# Create a new output directory under path_to_green
dirout = "%s/%s" % (path_to_green, output_directory)
if os.path.exists(dirout):
print("Warning: output directory '%s' already exists." % dirout)
else:
print("Creating output directory '%s'." % dirout)
os.mkdir(dirout)
# Loop over each directory fx, fy, fz
nsta = len(station_name)
for i in range(3):
# Set headers according to the orientation
if dirs[i][-1].upper() == "Z":
scale = -1 # change to positive up
else:
scale = 1
# Loop over each station
for j in range(nsta):
station = station_name[j]
stlo = station_lon[j]
stla = station_lat[j]
dirin = "%s/%s/%s" % (path_to_green, dirs[i], station)
print("Reading RGFs from %s:" % (dirin))
st = Stream()
for gradient in du:
fname = "%s/%s.%s" % (dirin, file_name, gradient)
st += read(fname, format="SAC")
# Set station headers
starttime = origin_time - t0
dist, az, baz = gps2dist_azimuth(event_lat, event_lon, stla, stlo)
# SAC headers
sacd = AttribDict()
sacd.stla = stla
sacd.stlo = stlo
sacd.evla = event_lat
sacd.evlo = event_lon
sacd.az = az
sacd.baz = baz
sacd.dist = dist / 1000 # convert to kilometers
sacd.o = 0
sacd.b = -1 * t0
sacd.cmpaz = cmpaz[i]
sacd.cmpinc = cmpinc[i]
sacd.kstnm = station
# Update start time
for tr in st:
tr.stats.starttime = starttime
tr.stats.distance = dist
tr.stats.back_azimuth = baz
# Sum displacement gradients to get reciprocal Green's functions
tensor = Stream()
for gradient, element in zip(["duxdx", "duydy", "duzdz"],
["XX", "YY", "ZZ"]):
trace = st.select(channel=gradient)[0].copy()
trace.stats.channel = "%s%s" % (orientation[i], element)
tensor += trace
trace = st.select(channel="duydx")[0].copy()
trace.data += st.select(channel="duxdy")[0].data
trace.stats.channel = "%s%s" % (orientation[i], "XY")
tensor += trace
trace = st.select(channel="duzdx")[0].copy()
trace.data += st.select(channel="duxdz")[0].data
trace.stats.channel = "%s%s" % (orientation[i], "XZ")
tensor += trace
trace = st.select(channel="duzdy")[0].copy()
trace.data += st.select(channel="duydz")[0].data
trace.stats.channel = "%s%s" % (orientation[i], "YZ")
tensor += trace
# Set sac headers before saving
print(" Saving GFs to %s" % dirout)
for tr in tensor:
tr.trim(origin_time, tr.stats.endtime)
tr.data = scale * tr.data
tr.stats.sac = sacd
sacout = "%s/%s.%.4f.%s" % (dirout, station, depth,
tr.stats.channel)
#print("Writing %s to file."%sacout)
tr.write(sacout, format="SAC")
