ObsPy Tutorial

Handling Event Metadata

Seismo-Live: http://seismo-live.org

Authors:

• Lion Krischer (@krischer)
• Tobias Megies (@megies)

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%matplotlib inline
import matplotlib.pyplot as plt
plt.style.use('ggplot')
plt.rcParams['figure.figsize'] = 12, 8

• for event metadata, the de-facto standard is QuakeML (an xml document structure)
• QuakeML files can be read using read_events()

from obspy import read_events

catalog = read_events("./data/event_tohoku_with_big_aftershocks.xml")
print(catalog)

• read_events() function returns a Catalog object, which is a collection of Event objects.

print(type(catalog))
print(type(catalog[0]))

event = catalog[0]
print(event)

• Event objects are again collections of other resources.
• the nested ObsPy Event class structure (Catalog/Event/Origin/Magnitude/FocalMechanism/...) is closely modelled after QuakeML

print(type(event.origins))
print(type(event.origins[0]))
print(event.origins[0])

print(type(event.magnitudes))
print(type(event.magnitudes[0]))
print(event.magnitudes[0])

# try event.<Tab> to get an idea what "children" elements event has

• The Catalog object contains some convenience methods to make working with events easier.
• for example, the included events can be filtered with various keys.

largest_magnitude_events = catalog.filter("magnitude >= 7.8")
print(largest_magnitude_events)

• There is a basic preview plot using the matplotlib basemap module.

catalog.plot(projection="local");

• a (modified) Catalog can be output to file (currently there is write support for QuakeML only)

largest_magnitude_events.write("/tmp/large_events.xml", format="QUAKEML")
!ls -l /tmp/large_events.xml

• the event type classes can be used to build up Events/Catalogs/Picks/.. from scratch in custom processing work flows and to share them with other researchers in the de facto standard format QuakeML

from obspy import UTCDateTime
from obspy.core.event import Catalog, Event, Origin, Magnitude
from obspy.geodetics import FlinnEngdahl

cat = Catalog()
cat.description = "Just a fictitious toy example catalog built from scratch"

e = Event()
e.event_type = "not existing"

o = Origin()
o.time = UTCDateTime(2014, 2, 23, 18, 0, 0)
o.latitude = 47.6
o.longitude = 12.0
o.depth = 10000
o.depth_type = "operator assigned"
o.evaluation_mode = "manual"
o.evaluation_status = "preliminary"
o.region = FlinnEngdahl().get_region(o.longitude, o.latitude)

m = Magnitude()
m.mag = 7.2
m.magnitude_type = "Mw"

m2 = Magnitude()
m2.mag = 7.4
m2.magnitude_type = "Ms"

# also included could be: custom picks, amplitude measurements, station magnitudes,
# focal mechanisms, moment tensors, ...

# make associations, put everything together
cat.append(e)
e.origins = [o]
e.magnitudes = [m, m2]
m.origin_id = o.resource_id
m2.origin_id = o.resource_id

print(cat)
cat.write("/tmp/my_custom_events.xml", format="QUAKEML")
!cat /tmp/my_custom_events.xml