DataAnalysis2022/ObsPy/02_UTCDateTime.ipynb

ObsPy Tutorial

Handling Time

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

Authors:

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

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This is a bit dry but not very difficult and important to know. It is used everywhere in ObsPy!

• All absolute time values are consistently handled with this class
• Based on a double precision POSIX timestamp for accuracy
• Timezone can be specified at initialization (if necessary)
• In Coordinated Universal Time (UTC) so no need to deal with timezones, daylight savings, ...

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

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Features of UTCDateTime

Initialization

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from obspy import UTCDateTime

print(UTCDateTime("2011-03-11T05:46:23.2"))        # mostly time strings defined by ISO standard
print(UTCDateTime("2011-03-11T14:46:23.2+09:00"))  # non-UTC timezone input
print(UTCDateTime(2011, 3, 11, 5, 46, 23, 2))
print(UTCDateTime(1299822383.2))

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# Current time can be initialized by leaving out any arguments
print(UTCDateTime())

Attribute Access

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time = UTCDateTime("2011-03-11T05:46:23.200000Z")
print(time.year)
print(time.julday)
print(time.timestamp)
print(time.weekday)
# try time.<Tab>

Handling time differences

• "+/-" defined to add seconds to an UTCDateTime object
• "-" defined to get time difference of two UTCDateTime objects

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time = UTCDateTime("2011-03-11T05:46:23.200000Z")
print(time)

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# one hour later
print(time + 3600)

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time2 = UTCDateTime(2012, 1, 1)
print(time2 - time)

Exercises

Calculate the number of days passed since the Tohoku main shock (the timestamp used above).

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Make a list of 10 UTCDateTime objects, starting today at 10:00 with a spacing of 90 minutes.

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Below is a list of strings with origin times of magnitude 8+ earthquakes since 2000 (fetched from IRIS). Assemble a list of interevent times in days. Use matplotlib to display a histogram.

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times = ["2001-06-23T20:33:09",
         "2003-09-25T19:50:07",
         "2004-12-23T14:59:00",
         "2004-12-26T00:58:52",
         "2005-03-28T16:09:35",
         "2006-06-01T18:57:02",
         "2006-06-05T00:50:31",
         "2006-11-15T11:14:14",
         "2007-01-13T04:23:23",
         "2007-04-01T20:39:56",
         "2007-08-15T23:40:58",
         "2007-09-12T11:10:26",
         "2009-09-29T17:48:11",
         "2010-02-27T06:34:13",
         "2011-03-11T05:46:23",
         "2012-04-11T08:38:36",
         "2012-04-11T10:43:10",
         "2013-05-24T05:44:48"]

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