# 5. Comparing seismic trends between LIGO sites¶

On Feb 13 2015 there was a massive earthquake in the Atlantic Ocean, that should have had an impact on LIGO operations, I’d like to find out.

First: we import the objects we need, one for getting the data:

``````from gwpy.timeseries import TimeSeriesDict
``````

and one for plotting the data:

``````from gwpy.plot import Plot
``````

Next we define the channels we want, namely the 0.03Hz-1Hz ground motion band-limited RMS channels (1-second average trends). We do this using string-replacement so we can substitute the interferometer prefix easily when we need to:

``````channels = [
'{ifo}:ISI-BS_ST1_SENSCOR_GND_STS_X_BLRMS_30M_100M.mean,s-trend',
'{ifo}:ISI-BS_ST1_SENSCOR_GND_STS_Y_BLRMS_30M_100M.mean,s-trend',
'{ifo}:ISI-BS_ST1_SENSCOR_GND_STS_Z_BLRMS_30M_100M.mean,s-trend',
]
``````

At last we can `get()` 12 hours of data for each interferometer:

``````lho = TimeSeriesDict.get([c.format(ifo='H1') for c in channels],
'Feb 13 2015 16:00', 'Feb 14 2015 04:00')
llo = TimeSeriesDict.get([c.format(ifo='L1') for c in channels],
'Feb 13 2015 16:00', 'Feb 14 2015 04:00')
``````

Next we can plot the data, with a separate `Axes` for each instrument:

``````plot = Plot(lho, llo, figsize=(12, 6), sharex=True, yscale='log')
ax1, ax2 = plot.axes
for ifo, ax in zip(('Hanford', 'Livingston'), (ax1, ax2)):
ax.legend(['X', 'Y', 'Z'])
ax.text(1.01, 0.5, ifo, ha='left', va='center', transform=ax.transAxes,
fontsize=18)
ax1.set_ylabel(r'\$1-3\$\,Hz motion [nm/s]', y=-0.1)
ax2.set_ylabel('')
ax1.set_title('Magnitude 7.1 earthquake impact on LIGO')
plot.show()
``````

As we can see, the earthquake had a huge impact on the LIGO observatories, severly imparing operations for several hours.