Seismo-Live: http://seismo-live.org
Authors:¶
- Martin van Driel (@martinvandriel)
- Lion Krischer (@krischer)
Overview:¶
Introduction:
- Part 1: Very basic introduction to the API, calculate the first seismogram.
Basic Tasks:
- Part 2: Some examples of interaction with obspy, calculate synthetics for a set of events and stations
Advanced Tasks:
- Part 3: Plot record section
- Part 4: Finite Source, compare to point source solution
Basic lines to set up the notebook and some paths.
%matplotlib inline
import matplotlib.pyplot as plt
import numpy as np
import os
import obspy
plt.style.use('ggplot')
plt.rcParams['figure.figsize'] = (10, 8)
Basic Instaseis API Introduction¶
Please also have a look at our webpage - http://www.instaseis.net/ - where everything is documented extensively.
Opening a Database¶
To get going you have to import the package instaseis.
import instaseis
An Instaseis database must be opened before it can be used. These can be either a local files computed with AxiSEM, or even more easily a remote database hosted by IRIS (http://ds.iris.edu/ds/products/syngine/).
db = instaseis.open_db("syngine://prem_a_10s")
Some basic information about the loaded database can be reviewed by just printing it.
print(db)
From this you can already glance a couple of aspects of the database used for this tutorial:
- uses anisotropic prem as its 1D model
- is accurate for periods down to 10 seconds
- includes vertical and horizontal components
- sources can have depths ranging from 0 to 700 km
- five hour long seismograms
To avoid delays that become relevant when requesting very many seismograms, IRIS also offers the databases for download.
Receivers and Sources¶
Instaseis calculates seismograms for any source and receiver pair. A receiver has coordinates and optionally network and station codes. Using a reciprocal database, all receivers are assumed to be at the same depth, i.e. usually at the Earth surface.
rec = instaseis.Receiver(latitude=44.06238, longitude=10.59698,
network="IV", station="BDI")
print(rec)
Sources are naturally a bit more complex and Instaseis offers a variety of ways to define them. A straightforward way for earthquakes is to pass coordinates, moment as well as strike, dip and rake.
src = instaseis.Source.from_strike_dip_rake(
latitude=27.77, longitude=85.37, depth_in_m=12000.0,
M0=1e+21, strike=32., dip=62., rake=90.)
print(src)
Note that origin time was not provided and hence defaults to 1970. A non double-couple source can directly be specified in terms of its moment tensor (note that instaseis uses SI units, i.e. NM, while GCMT uses dyn cm).
src = instaseis.Source(
latitude=27.77, longitude=85.37, depth_in_m=12000.0,
m_rr=8.29e+20, m_tt=-2.33e+20, m_pp=-5.96e+20,
m_rt=2.96e+20, m_rp=4.74e+20, m_tp=-3.73e+20)
print(src)
Sidenote: The moment tensor can be visualized using the Beachball function from obspy.imaging:
from obspy.imaging.beachball import beachball
mt = src.tensor / src.M0 # normalize the tensor to avoid problems in the plotting
beachball(mt, size=200, linewidth=2, facecolor='b');
Now we are ready to extract synthetic seismograms from the database. The return type is an obspy stream object, which can directly be plotted:
st = db.get_seismograms(source=src, receiver=rec, components='ZNERT')
print(st)
st.plot();
Done This is all you need for a basic usage of Instaseis!