ObsPy Tutorial
Handling Time
</div> </div> </div> image: User:Abbaszade656 / Wikimedia Commons / CC-BY-SA-4.0

## Workshop for the "Training in Network Management Systems and Analytical Tools for Seismic"¶

### Baku, October 2018¶

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

##### Authors:¶

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 nanosecond precision POSIX integer 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, ...

In [1]:
%matplotlib inline
import matplotlib.pyplot as plt
plt.style.use('ggplot')
plt.rcParams['figure.figsize'] = 12, 8


## Features of UTCDateTime¶

#### Initialization¶

In [2]:
from obspy import UTCDateTime

print(UTCDateTime("2014-08-24T10:20:44.0"))        # mostly time strings defined by ISO standard
print(UTCDateTime("2014-08-24T01:20:44.0-09:00"))  # non-UTC timezone input
print(UTCDateTime(2014, 8, 24, 10, 20, 44))        # year, month, day, hour, min, sec, musec
print(UTCDateTime(1408875644.0))                   # timestamp

2014-08-24T10:20:44.000000Z
2014-08-24T10:20:44.000000Z
2014-08-24T10:20:44.000000Z
2014-08-24T10:20:44.000000Z

In [3]:
# Current time can be initialized by leaving out any arguments
print(UTCDateTime())

2019-11-04T08:59:32.256536Z


#### Attribute Access¶

In [4]:
time = UTCDateTime("2014-08-24T10:20:44.0")
print(time.year)
print(time.julday)
print(time.timestamp)
print(time.weekday)
# try time.<Tab>

2014
236
1408875644.0
6


#### Handling time differences¶

• "+/-" defined to add seconds to an UTCDateTime object
• "-" defined to get time difference of two UTCDateTime objects
In [5]:
time = UTCDateTime("2014-08-24T10:20:44.0")
print(time)

2014-08-24T10:20:44.000000Z

In [6]:
# one hour later
print(time + 3600)

2014-08-24T11:20:44.000000Z

In [7]:
# Time differences
time2 = UTCDateTime(2015, 1, 1)
print(time2 - time)

11194756.0


### Exercises¶

Calculate the number of days passed since the 2014 South Napa earthquake (the timestamp used above).

In [8]:
print((UTCDateTime() - UTCDateTime("2014-08-24T11:20:44.000000Z")) / 86400)

1897.901947792662


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

In [9]:
t = UTCDateTime(2017, 9, 18, 10)

times = []
for i in range(10):
t2 = t + i * 90 * 60
times.append(t2)

times

Out[9]:
[2017-09-18T10:00:00.000000Z,
2017-09-18T11:30:00.000000Z,
2017-09-18T13:00:00.000000Z,
2017-09-18T14:30:00.000000Z,
2017-09-18T16:00:00.000000Z,
2017-09-18T17:30:00.000000Z,
2017-09-18T19:00:00.000000Z,
2017-09-18T20:30:00.000000Z,
2017-09-18T22:00:00.000000Z,
2017-09-18T23:30:00.000000Z]

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.

In [10]:
times = ["2000-11-16T04:54:56",
"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",
"2006-05-03T15:26:39",
"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",
"2012-04-11T08:38:37",
"2012-04-11T10:43:10",
"2013-05-24T05:44:49",
"2014-04-01T23:46:47",
"2015-09-16T22:54:32",
"2017-09-08T04:49:21"]

In [11]:
import matplotlib.pyplot as plt

inter_event_times = []

for i in range(1, len(times)):
dt = UTCDateTime(times[i]) - UTCDateTime(times[i-1])
dt = dt / (3600 * 24)
inter_event_times.append(dt)

plt.hist(inter_event_times, bins=range(0, 1000, 100))
plt.xlabel("Magnitude 8+ interevent times since 2000 [days]")
plt.ylabel("count")
plt.show()