It looks like you're using an Ad Blocker.
Please white-list or disable AboveTopSecret.com in your ad-blocking tool.
Some features of ATS will be disabled while you continue to use an ad-blocker.
From observing and analyzing many earthquakes, we know the relationship between the S-P time and the distance between the station and the earthquake. We can therefore convert each measured S-P time to
distance. A time interval of 1.5 minutes corresponds to a distance of 900 kilometers, 3 minutes to 1800 kilometers, and 5 minutes to 3300 kilometers.
The hypocenters of 43 earthquakes on Kilauea Volcano were analyzed in detail in order to examine the accuracy of hypocenters determined with data from tripartite arrays and to look for evidence of zones of abnormally high or low velocity in a region of complex crustal structure. Ten vertical and two horizontal seismometers were operated on the south flank of Kilauea within the seismic network of the Hawaiian Volcano Observatory. A number of combinations of the temporary stations were treated as separate tripartite arrays. The sides of each tripartite array were 1 to 2 km long. Azimuths and apparent velocities of P-wave fronts observed at these arrays generally agreed well with the values predicted from hypocenters calculated using data from as many as 20 stations. Some observed azimuths differed from the predicted values by over 40° and some apparent velocities differed by nearly a factor of 2. These differences are consistent with the travel-time residuals found when the hypocenters are located with all available data. They can be attributed to local zones of abnormally high or low velocity or to changes in the thicknesses of the assumed crustal layers. Waves that travel through the east and southwest rift zones arrive relatively early and the waves traveling through the Kaoiki fault zone arrive late. Refraction data were compiled to obtain a new average crustal structure. When small tripartite arrays are used to locate shallow earthquakes, a crustal structure with a linear increase in velocity should be assumed in order to calculate unique hypocenters and to obtain less scatter in a group of hypocenters.
Abstract Earthquake location catalogs are not an exact representation of the true earthquake locations. They contain random error, for example from errors in the arrival time picks, as well as systematic biases. The most important source of systematic errors in earthquake locations is the inherent dependence of earthquake locations on the assumed seismic velocity structure of the Earth. Random errors may be accounted for in formal uncertainty estimates, but systematic biases are not, and they must be considered based on knowledge about how the earthquakes were located. In this article we discuss earthquake location methods and methods for estimating formal uncertainties; we consider systematic biases in earthquake location catalogs; and we give readers guidance on how to identify good-quality earthquake locations.
Global centroid catalogs are also sometimes used in statistical studies. The earthquake centroid, the center of moment, is often offset rom the hypocenter by several 10s of km or more, so the locations from the centroid catalogs are not directly comparable to hypocenter location catalogs. It is important to choose the catalog appropriate for the scientific question at hand: if one is interested in where earthquakes nucleate, a hypocenter catalog is preferable; while if one is interested in where the most slip occurs, a centroid catalog is more appropriate. The location uncertainty of centroid catalogs is similar to that of other global location catalogs.
I was sitting on my duff Saturday night
There are now five regions of the world where seismic tension is registering higher than normal: California, the Virgin Islands of the Caribbean plate, Alaska, the Philippines, and Indonesia. Any of these regions are primed for the eruption of large-scale seismic events. People in high-risk seismic zones should remain alert for the potential occurrence of potentially hazardous seismic or volcanic episodes./ex]edit on 5-9-2012 by SpaceJockey1 because: Oops spelling
WEHW42 PHEB 051451
TSUNAMI INFORMATION STATEMENT NUMBER 1
NWS PACIFIC TSUNAMI WARNING CENTER EWA BEACH HI
451 AM HST WED SEP 05 2012
TO - CIVIL DEFENSE IN THE STATE OF HAWAII
SUBJECT - TSUNAMI INFORMATION STATEMENT
THIS STATEMENT IS FOR INFORMATION ONLY. NO ACTION REQUIRED.
AN EARTHQUAKE HAS OCCURRED WITH THESE PRELIMINARY PARAMETERS
ORIGIN TIME - 0442 AM HST 05 SEP 2012
COORDINATES - 9.9 NORTH 85.5 WEST
LOCATION - OFF COAST OF COSTA RICA
MAGNITUDE - 7.9 MOMENT
THE PACIFIC TSUNAMI WARNING CENTER HAS ISSUED AN EXPANDING
REGIONAL TSUNAMI WARNING AND WATCH FOR PARTS OF THE PACIFIC
LOCATED CLOSER TO THE EARTHQUAKE. AN EVALUATION OF THE PACIFIC
WIDE TSUNAMI THREAT IS UNDERWAY AND THERE IS A POSSIBILITY THAT
HAWAII COULD BE ELEVATED TO A WATCH OR WARNING STATUS.
IF TSUNAMI WAVES IMPACT HAWAII THEIR ESTIMATED EARLIEST ARRIVAL
0243 PM HST WED 05 SEP 2012
THIS WILL BE THE ONLY STATEMENT ISSUED FOR THIS EVENT UNLESS
ADDITIONAL DATA ARE RECEIVED.
Preferred Location Parameters
± 13.6 km
± 6.2 km
There are now five regions of the world where seismic tension is registering higher than normal: