A Comprehensive Study of Precursory Quiescence Before       Great and Large Earthquakes in the Central Aleutians and    Chile
{'Code': '06030204', 'Directorate': {'Abbreviation': 'GEO', 'LongName': 'Directorate For Geosciences'}, 'Division': {'Abbreviation': 'EAR', 'LongName': 'Division Of Earth Sciences'}}
{'SignBlockName': 'Patricia Brooking', 'PO_EMAI': None, 'PO_PHON': None}
Four large and great earthquakes have occurred in the Central Aleutians         and Valparaiso, Chile regions since 1971.  All of these events have had         precursory quiescence reported prior to them.  Several observations             sugget that the reported precursors to events in these regions during           1971 reflect systematic changes in teleseismic magnitude estimates              rather than real changes in seismicity rates.  These include: 1) Both           seismicity rate decreases can be observed in regions which are much             larger than the rupture zones of the events; 2) the distribution of the         rate changes in the Chile region in the magnitude domain can be well            modeled as being due to changes in magnitudes; and 3) the change in the         Aleutians is strong in sets with a magnitude cutoff and a weak in all           events, a characteristic expected for changes in magnitudes.  The               average number of stations used for teleseismic magnitude estimates in          Chile is less than 10, which is probably too small to provide magnitudes        which are independent of station biases.  We propose to redetermine the         teleseismic magnitudes for these regions using station magnitude                corrections and to re-examine the seismicity patterns prior to the              large events to determine whether the reported precursors are real or           due to systematic changes in magnitudes.  We plan to integrate these            observations with local seismic network data from each region to                increase our understanding of the magnitude distribution of real                precursory rate variations if they exist.  This work is crucial for             understanding what precursors exist prior to these events.  More                importantly, it is critical for understanding the strengths and                 weaknesses of seismicity data and avoiding making serious errors in             interpreting these data for earthquake predictions.
{'FirstName': 'Ray', 'LastName': 'Habermann', 'PI_MID_INIT': 'E', 'PI_SUFX_NAME': None, 'PI_FULL_NAME': 'Ray E Habermann', 'EmailAddress': 'haber@ngdc.noaa.gov', 'NSF_ID': '000386987', 'StartDate': '08/01/1987', 'EndDate': None, 'RoleCode': 'Principal Investigator'}
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