Our last study found that deepest-depth earthquakes with larger magnitudes (M6 or above) showed seasonality, which is dependent on the area searched. The main results indicated strong evidence that the causes for the delays in enhancements along the period investigated were due to the tectonics also, not only the season. Therefore, if the inquiry was about an area in Northern Hemisphere, the season in which the increases occurred is different than the season in the Southern Hemisphere. Also, higher latitudes in the Northern Hemisphere or around the Equator, displayed seasonality similarly where the tremors appear to increase during the Spring and Summer. This did not happen to the Southern Hemisphere where disturbances and anomalies occurred without showing much connection to the seasons in the analyzed period. However, some of the regions presented periodicities independent from the seasons.
In the first study [
We also decided to verify a former paper [
The results around the Circum Pacific area showed that Northern Hemisphere regions had similar reactions for the seasons, as expected. The Southern Hemisphere also had feedback, but the enhancements dependencies appeared to be beyond the seasons.
The next sections will describe our statistical, mathematical model and how it is used to find the relationship between seasons and enhancement of events in the five chosen areas.
Our method to determine if earthquakes increase, decrease, or remain constant in each region and depth begins with defining the regions with occurrences of earthquakes at depths of ≥500 km. There are five areas chosen: North Pacific (Japan, Russia), Philippines (including part of Northern Mariana Islands), South Pacific (essentially the area around Indonesia), South America, and Fiji surrounds (including the Vanuatu region). The period analyzed is 1987-2017 or 30 years. We used the magnitudes of M ≥ 2.5, which is the minimum value of our working catalogs [
In this paper, the extended periods are statistically productive and point to better results. We constructed tables of N values for each year searched and determined the average number of events per year by dividing the sum of all recorded events by 30.
The dataset is comprised of earthquakes recorded during the period mentioned. The sum of data values was y1 = data recorded in the chosen year level D ≥ 500 km for the depths in the region X (A, B, C,D,E)
∑ n 0 n n Y n = y n 0 + y n 1 + ⋯ + y n n (1)
where n = 1987, ∙∙∙, 2017, and range n’ is 30 years.
The mean is defined as
Mean = M = ∑ n 0 n n Y n 30 (2)
Datavalue − mean = Y ′ n (3)
If Y ′ n > M , the value is higher than one during that year and it means the number of earthquakes exceeds the average. On the other hand, if Y ′ n < M , the number will be less than one during that year, indicating that the number of earthquakes was below the average. It is also possible to have a result of zero (was not common, most of the dataset), which would mean there was no available data.
Calculating variance from annual averages will help to define and explain the locations where ultra-deep earthquakes (UDQ) occur.
The coordinates to construct our mathematical models are displayed in
The coordinates make a subdivision of areas where UDQ happen. Although it is clearly defined at the Northern and Southern Hemisphere, it is not possible to comprise all the locations with deepest earthquakes within these coordinates. Regardless, the five places give a fair idea of a possible seasonality.
North Hemisphere | Coordinates |
---|---|
North Pacific | 67.067N, 30.449S, −144.844E, −226.934W |
Philippines, Mariana’s | 20.633N, 1.862S, −223.94E, −252.246W |
South Hemisphere | |
South Pacific | 10.207N, −16.236S, −184.922E, −263.672W |
South America | 5.545N, −53.54S, −65.215E, −87.539W |
Fiji | −9.243N, −35.29S, −197.227W, −119.18E |
North Hemisphere | Range | South Hemisphere | Range |
---|---|---|---|
Spring | March 1- May 31 | Spring | Sept 1-Nov 30 |
Summer | Jun 1- Aug 31 | Summer | Dec 1-Feb 28 |
Fall | Sept 1- Nov 30 | Fall | March 1-May 30 |
Winter | Dec 1- Feb 28 | Winter | Jun 1-Aug 31 |
With
The next
Using
The next two tables,
The next table,
Year | January | February | March | April | May | June | July | August | September | October | November | December |
---|---|---|---|---|---|---|---|---|---|---|---|---|
1987 | 0.3 | 1.3 | 0.7 | 0.7 | 1.2 | 0.3 | 0.8 | 0.2 | 0 | 0.8 | 0.3 | 0.5 |
1988 | 0 | 0 | 0.3 | 0 | 0.5 | 0.3 | 0.5 | 0.5 | 0.5 | 0 | 0.3 | 0 |
1989 | 0.7 | 0 | 0 | 0.3 | 0.5 | 0 | 0.8 | 0.2 | 1 | 0 | 0 | 0.5 |
1990 | 1 | 0.7 | 0.3 | 1 | 0.5 | 0 | 0.2 | 0.8 | 1.5 | 0.8 | 0.8 | 1 |
1991 | 0.3 | 0 | 0 | 0.7 | 0.8 | 0 | 1.2 | 0.8 | 0.5 | 0 | 0.3 | 0.5 |
1992 | 2.3 | 0.3 | 0.7 | 0.7 | 1 | 1 | 1 | 0.5 | 0 | 0.3 | 1 | 0 |
1993 | 1 | 0.3 | 0.7 | 0.3 | 0.5 | 0.7 | 0 | 0.5 | 0.5 | 0.8 | 1.3 | 0.5 |
1994 | 1 | 0.7 | 0.3 | 0.3 | 0 | 0 | 0.2 | 0.2 | 1 | 0.3 | 0.3 | 0.5 |
1995 | 0.7 | 1.3 | 0 | 1.3 | 0 | 0.7 | 4.5 | 4.5 | 1 | 2 | 1 | 1.5 |
1996 | 0.7 | 0.7 | 2.3 | 0 | 1 | 2 | 1 | 1 | 1.5 | 1 | 0.3 | 2.5 |
1997 | 1.3 | 0 | 0.7 | 1.3 | 1.5 | 0.7 | 1 | 1 | 0.5 | 1 | 0.8 | 4 |
1998 | 1.3 | 4 | 1.3 | 2.3 | 0.8 | 2 | 0.8 | 0.8 | 2.5 | 0.3 | 1 | 0 |
1999 | 1 | 0.7 | 2 | 2 | 0.2 | 0.7 | 0.8 | 0.8 | 1.5 | 1.3 | 1 | 0.5 |
2000 | 1 | 1 | 1.3 | 0 | 0.8 | 1 | 0.2 | 0.2 | 1 | 0.3 | 0.3 | 1.5 |
2001 | 0.3 | 1 | 0 | 1 | 1.5 | 1 | 1 | 1 | 1.5 | 1 | 0 | 1 |
2002 | 1.7 | 1.3 | 1 | 0 | 3 | 1 | 1.5 | 1.5 | 2 | 0.3 | 2 | 2 |
2003 | 1.3 | 0.7 | 1.7 | 1.3 | 2 | 1.6 | 1.3 | 1.3 | 5 | 1.7 | 2 | 1.5 |
2004 | 0.3 | 1.3 | 1.7 | 2 | 0.8 | 1.6 | 1.5 | 1.5 | 2 | 2 | 1.3 | 1.5 |
2005 | 0.3 | 3.3 | 1 | 1 | 1 | 1.6 | 1.5 | 1.5 | 2 | 3 | 1.6 | 1 |
2006 | 1.3 | 0.7 | 0.3 | 0.3 | 1.4 | 1.6 | 1.3 | 1.3 | 1.5 | 2 | 3.6 | 1.5 |
2007 | 2 | 1.3 | 1.7 | 0.7 | 2.5 | 1.6 | 1 | 1 | 1.5 | 2 | 2 | 2.5 |
2008 | 1.7 | 0.7 | 0.7 | 2.3 | 0.2 | 1.6 | 1 | 1 | 2.5 | 2 | 1 | 2.5 |
2009 | 1.3 | 0 | 1 | 0.7 | 0 | 0 | 0.5 | 0.5 | 0 | 2.3 | 0.3 | 0.5 |
2010 | 0 | 1 | 0.3 | 0 | 0.8 | 0 | 1.5 | 1.5 | 0.5 | 1.3 | 0.3 | 0.5 |
2011 | 0.3 | 0.7 | 1.7 | 0.3 | 0.2 | 0.3 | 0.2 | 2 | 0 | 1.3 | 0.6 | 1.5 |
2012 | 0.3 | 1 | 0 | 0.7 | 0.2 | 1.6 | 0.8 | 1 | 0 | 0.7 | 0.3 | 0 |
2013 | 0 | 0 | 0 | 1.3 | 3 | 1.6 | 0.2 | 0.5 | 1.5 | 2.3 | 1 | 2.5 |
2014 | 1.7 | 1 | 1.7 | 2 | 2 | 1.3 | 1 | 1.5 | 1.5 | 1.3 | 0.6 | 2 |
2015 | 0.7 | 1.7 | 1.3 | 0.7 | 1.5 | 1 | 0.8 | 0.8 | 1.5 | 1.3 | 1.6 | 2.5 |
2016 | 1.7 | 0.7 | 0.7 | 1.3 | 1.2 | 0.7 | 0.5 | 0.5 | 2.5 | 1 | 1.3 | 0.5 |
2017 | 1.7 | 0.7 | 1.7 | 1.3 | 1.2 | 1.6 | 1.1 | 1.3 | 2 | 1.7 | 1 | 1.5 |
North Pacific seasons | |
---|---|
Months | Averages |
January (Winter) | 3 |
May (Spring) | 5 |
July (Summer) | 4 |
October (Fall) | 3 |
for the 31% of total activity for the year, followed closely by Spring.
Next, we analyze the Southern Hemisphere and some of the chosen regions, such as those identified in
Year | January | February | March | April | May | June | July | August | September | October | November | December |
---|---|---|---|---|---|---|---|---|---|---|---|---|
1987 | 0.5 | 2 | 0.5 | 0.5 | 2 | 0.5 | 0.5 | 0 | 0 | 0.5 | 0 | 0.5 |
1988 | 0 | 0 | 0.5 | 0 | 0 | 0 | 0 | 0.5 | 0 | 0 | 0 | 0 |
1989 | 0.5 | 0 | 0 | 0 | 0.5 | 0 | 0.5 | 0 | 0.5 | 0 | 0 | 0.5 |
1990 | 0.5 | 0.5 | 0.5 | 0 | 0 | 0 | 0 | 1 | 0 | 0.5 | 0 | 0 |
1991 | 0 | 0 | 0 | 0.5 | 1 | 1 | 0 | 0 | 0 | 0 | 0.5 | 0.5 |
1992 | 3 | 0 | 1 | 0.5 | 0 | 0 | 1 | 0.5 | 0 | 0.5 | 1 | 0 |
1993 | 1 | 0.5 | 0 | 0 | 1 | 0 | 0 | 0.5 | 0.5 | 0.5 | 0.5 | 0 |
1994 | 0 | 0 | 0 | 0 | 0 | 0 | 0.5 | 0 | 0 | 0.5 | 0 | 0 |
1995 | 0 | 0.5 | 0 | 0.5 | 0 | 0 | 1 | 0.5 | 0 | 0.5 | 1 | 0.5 |
1996 | 0.5 | 1 | 1 | 0.5 | 1 | 3 | 0 | 0.5 | 0.5 | 1 | 0.5 | 1 |
1997 | 0 | 0 | 2 | 0.5 | 2 | 0.5 | 0 | 1 | 1 | 1 | 0 | 3 |
1998 | 1 | 1 | 0 | 2 | 1 | 2 | 0.5 | 0 | 2 | 0 | 0.5 | 0 |
1999 | 0 | 1 | 0.5 | 0.5 | 0 | 1 | 0 | 0 | 0 | 2 | 2 | 0.5 |
2000 | 0.5 | 0 | 2 | 0 | 0.5 | 0.5 | 2 | 0.5 | 0 | 0 | 0.5 | 0 |
2001 | 0 | 1 | 1 | 2 | 1 | 0.5 | 0 | 0 | 0.5 | 0.5 | 0 | 0 |
2002 | 2 | 0 | 1 | 0 | 0 | 1 | 0.5 | 0.5 | 2 | 0.5 | 1 | 0.5 |
2003 | 1 | 0 | 0 | 2 | 3 | 0 | 0.5 | 1 | 0 | 1 | 2 | 0.5 |
2004 | 0 | 2 | 1 | 1 | 1 | 2 | 1 | 0.5 | 1 | 0 | 1 | 0.5 |
2005 | 0.5 | 3 | 0.5 | 1 | 0.5 | 1 | 0.5 | 3 | 0.5 | 0.5 | 2 | 0 |
2006 | 2 | 1 | 0 | 0 | 1 | 2 | 3 | 2 | 1 | 3 | 4 | 2 |
2007 | 2 | 0.5 | 1 | 0 | 0.5 | 0.5 | 1 | 0.5 | 1 | 0 | 2 | 0 |
2008 | 2 | 0.5 | 0.5 | 1 | 1 | 1 | 1 | 0.5 | 2 | 0.5 | 0.5 | 2 |
2009 | 2 | 0 | 1 | 0 | 0.5 | 0.5 | 0.5 | 0 | 0 | 4 | 0 | 0 |
2010 | 0 | 0.5 | 0.5 | 0 | 0 | 0 | 10 | 3 | 0 | 1 | 0.5 | 0.5 |
2011 | 1 | 2 | 0 | 0 | 1 | 0.5 | 0.5 | 0.5 | 0 | 1 | 1 | 1 |
2012 | 0.5 | 0.5 | 0 | 1 | 0.5 | 2 | 0.5 | 0 | 0.5 | 1 | 0 | |
2013 | 0 | 0 | 0 | 0.5 | 0 | 0 | 0.5 | 1 | 0.5 | 2 | 0.5 | 1 |
2014 | 1 | 1 | 2 | 2 | 1 | 0 | 0.5 | 2 | 1 | 1 | 0.5 | 1 |
2015 | 0.5 | 0.5 | 1 | 1 | 1 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 2 | 2 |
2016 | 2 | 0.5 | 0.5 | 2 | 1 | 1 | 0.5 | 0.5 | 0 | 0.5 | 2 | 0.5 |
2017 | 2 | 0.5 | 0.5 | 1 | 0.5 | 0 | 1 | 2 | 0 | 1 | 1 | 1 |
Philippines seasons | average |
---|---|
January (Winter) | 2 |
May (Spring) | 3 |
July (Summer) | 3 |
November(Fall) | 2 |
Year | January | February | March | April | May | June | July | August | September | October | November | December |
---|---|---|---|---|---|---|---|---|---|---|---|---|
1987 | 1 | 3 | 0.5 | 1 | 0 | 0 | 0 | 1 | 1 | 0.5 | 3 | 0.5 |
1988 | 0 | 0 | 1.5 | 0 | 1 | 1 | 0 | 0 | 0 | 1 | 0 | 2.5 |
1989 | 0 | 1 | 0.5 | 1 | 0 | 0 | 0.5 | 1 | 0.5 | 0 | 0 | 0.5 |
1990 | 1 | 0 | 0 | 0 | 1 | 1 | 3 | 2 | 1 | 0.5 | 1 | 0 |
1991 | 0 | 0 | 0 | 0 | 0 | 1 | 0.5 | 1 | 1 | 0 | 0 | 1.5 |
1992 | 0 | 0 | 1 | 1 | 0 | 2 | 0 | 1 | 0 | 0.5 | 1 | 0.5 |
1993 | 0 | 0 | 0.5 | 0 | 0 | 0 | 0.5 | 1 | 0.5 | 0 | 1 | 0 |
1994 | 0 | 0 | 0.5 | 2 | 0.5 | 0 | 0 | 3 | 1 | 0.5 | 1 | 0 |
1995 | 0 | 0 | 0 | 0 | 1.5 | 1 | 0.5 | 1 | 0 | 1.5 | 0 | 1.5 |
1996 | 3 | 1 | 0.5 | 0 | 0.5 | 1 | 9 | 3 | 0 | 2 | 1 | 0.5 |
1997 | 5 | 1 | 1.5 | 0 | 0.5 | 1 | 2 | 1 | 0.5 | 0 | 0 | 0.5 |
1998 | 1 | 1 | 0 | 1 | 1.5 | 2 | 0 | 0 | 0 | 1 | 1 | 1 |
1999 | 0 | 3 | 0.5 | 0 | 0 | 0 | 0 | 0 | 0 | 2.5 | 0 | 0 |
2000 | 1 | 1 | 0 | 3 | 0.5 | 1 | 1 | 4 | 2 | 0.5 | 1 | 0.5 |
2001 | 0 | 3 | 0.5 | 1 | 0.5 | 0 | 1.5 | 0 | 1 | 0 | 1 | 0.5 |
2002 | 0 | 2 | 0.5 | 0 | 0.5 | 2 | 1 | 2 | 0 | 1.5 | 2 | 1.5 |
2003 | 1 | 1 | 0.5 | 1 | 3 | 3 | 0.5 | 2 | 1 | 1 | 0 | 0 |
2004 | 6 | 0 | 1 | 3 | 2 | 7 | 2 | 2 | 3 | 1 | 2 | 0 |
2005 | 1 | 1 | 1 | 3 | 1 | 2 | 2.5 | 1 | 1 | 0.5 | 1 | 1.5 |
2006 | 1 | 3 | 2.5 | 1 | 0.5 | 2 | 0.5 | 0 | 1 | 1 | 3 | 1 |
2007 | 1 | 2 | 1.5 | 3 | 1.5 | 4 | 2.5 | 1 | 1 | 0.5 | 1 | 1.5 |
2008 | 1 | 1 | 1 | 1 | 0.5 | 0 | 1.5 | 2 | 0.5 | 1.5 | 1 | 4 |
2009 | 1 | 1 | 0.5 | 2 | 0.5 | 1 | 0 | 0 | 0.5 | 1 | 0 | 0.5 |
2010 | 3 | 0 | 0.5 | 0 | 0.5 | 0 | 0 | 1 | 0.5 | 0.5 | 0 | 0.5 |
2011 | 1 | 0 | 1 | 0 | 0.5 | 0 | 0 | 2 | 0.5 | 0 | 2 | 0.5 |
2012 | 1 | 0 | 2 | 1 | 0.5 | 0 | 0 | 1 | 0.5 | 0.5 | 0 | 1 |
2013 | 1 | 1 | 0.5 | 0 | 0.5 | 0 | 0.5 | 2 | 1 | 2 | 2 | 0.5 |
2014 | 3 | 2 | 0.5 | 1 | 1 | 1 | 0.5 | 3 | 2 | 2 | 3 | 1.5 |
2015 | 1 | 7 | 1.5 | 1 | 1 | 0 | 1.5 | 3 | 0.5 | 2 | 0 | 1.5 |
2016 | 3 | 2 | 2.5 | 1 | 2 | 3 | 0 | 2 | 1 | 1 | 2 | 2 |
2017 | 2 | 3 | 1 | 1 | 1 | 1 | 0.5 | 3 | 2.5 | 1.5 | 1 | 1 |
conditions formerly defined. South Hemisphere, presented months with a lack of earthquakes as indicated with zero, in higher number than Northern, within the average indicated as one, and enhancement months, when only the values above 1.5 were considered for results. We found anomalies higher than those at the North Hemisphere, which means several years presented one or two months with common occurrences above than normal. In Indonesia, it was highest in 1996 (July), in 2004 (January and June), and in 2015 (February). Those anomalies are not involved in our calculations as particularly crucial for the seasonality of the location and had little influence on the estimates.
Consulting
Thus, South Pacific (Indonesia area) results showed that UDQ independent of the magnitude value did not display seasonality such as that seen in the North Hemisphere.
Indonesia season | average |
---|---|
March (Fall) | 1.7 |
July (Winter) | 1.9 |
October (Spring) | 1.8 |
December (Summer) | 1.8 |
The deep depth earthquakes in South America usually do not have many events in a year. If you observe
There are anomalies in
Year | January | February | March | April | May | June | July | August | September | October | November | December |
---|---|---|---|---|---|---|---|---|---|---|---|---|
1987 | 1 | 2 | 0 | 2 | 1 | 1 | 0 | 2 | 1 | 1 | 4 | 0 |
1988 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 1 |
1989 | 0 | 1 | 0 | 0 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
1990 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 1 | 1 |
1991 | 1 | 2 | 0 | 0 | 0 | 4 | 1 | 0 | 0 | 0 | 0 | 0 |
1992 | 0 | 0 | 0 | 0 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
1993 | 0 | 2 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 |
1994 | 1 | 0 | 0 | 1 | 0 | 2 | 0 | 0 | 0 | 0 | 3 | 1 |
1995 | 1 | 0 | 1 | 0 | 2 | 0 | 0 | 0 | 0 | 0 | 3 | 0 |
1996 | 1 | 0 | 0 | 1 | 1 | 0 | 0 | 1 | 1 | 0 | 0 | 1 |
1997 | 0 | 1 | 4 | 1 | 2 | 1 | 1 | 0 | 0 | 0 | 1 | 1 |
1998 | 1 | 0 | 1 | 2 | 1 | 0 | 1 | 0 | 1 | 1 | 1 | 1 |
1999 | 0 | 1 | 1 | 0 | 0 | 1 | 1 | 0 | 1 | 0 | 0 | 1 |
2000 | 0 | 1 | 0 | 3 | 0 | 1 | 0 | 2 | 0 | 0 | 0 | 0 |
2001 | 0 | 0 | 2 | 1 | 1 | 0 | 0 | 1 | 0 | 0 | 0 | 0 |
2002 | 0 | 0 | 0 | 1 | 3 | 1 | 0 | 1 | 0 | 1 | 1 | 0 |
2003 | 0 | 2 | 2 | 1 | 0 | 1 | 1 | 3 | 0 | 0 | 0 | 0 |
2004 | 1 | 1 | 0 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 1 |
2005 | 2 | 0 | 2 | 1 | 1 | 0 | 1 | 0 | 1 | 1 | 1 | 0 |
2006 | 0 | 0 | 3 | 1 | 1 | 0 | 1 | 1 | 2 | 0 | 2 | 0 |
2007 | 0 | 2 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 0 | 1 | 0 |
2008 | 1 | 1 | 0 | 2 | 1 | 0 | 1 | 0 | 2 | 1 | 1 | 1 |
2009 | 1 | 0 | 0 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 2 | 0 |
2010 | 2 | 0 | 0 | 1 | 1 | 0 | 1 | 1 | 0 | 0 | 2 | 0 |
2011 | 0 | 2 | 0 | 3 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 0 |
2012 | 0 | 0 | 1 | 0 | 3 | 5 | 0 | 0 | 0 | 2 | 1 | 1 |
2013 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 |
2014 | 2 | 0 | 0 | 2 | 1 | 0 | 1 | 0 | 0 | 1 | 4 | 0 |
2015 | 1 | 0 | 1 | 1 | 1 | 0 | 0 | 1 | 2 | 1 | 20 | 3 |
2016 | 3 | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 3 | 3 | 1 |
2017 | 0 | 2 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 |
Seasons | average |
---|---|
February (Summer) | 1.4 |
March (Fall) | 1.5 |
June (Summer) | 1.5 |
Oct/Nov. (Spring) | 1.3 |
Year | January | February | March | April | May | June | July | August | September | October | November | December |
---|---|---|---|---|---|---|---|---|---|---|---|---|
1987 | 0.5 | 0 | 0.5 | 0.5 | 0.5 | 0 | 0.5 | 0.5 | 0.5 | 0 | 0.5 | 0.5 |
1988 | 0 | 1 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 0 | 0.5 | 0 |
1989 | 0 | 0 | 0.5 | 0.5 | 0.5 | 0 | 0.5 | 0.5 | 0.5 | 1 | 0.5 | 0.5 |
1990 | 0.5 | 0.5 | 0.5 | 0 | 0.5 | 0.5 | 1 | 0 | 0.5 | 1 | 0.5 | 0 |
1991 | 1 | 0 | 0 | 0.5 | 0 | 0.5 | 0.5 | 0 | 0 | 0.5 | 0 | 1 |
1992 | 0.5 | 0 | 0 | 0 | 1 | 0.5 | 0 | 1 | 0.5 | 0 | 0 | 0.5 |
1993 | 0.5 | 0 | 0.5 | 1 | 1 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 0 | 0.5 |
1994 | 0 | 0 | 1 | 1 | 0.5 | 0 | 0.5 | 1 | 0.5 | 0 | 0.5 | 0 |
1995 | 0.5 | 0 | 1.0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0.5 |
1996 | 1 | 1 | 1 | 1 | 1 | 1 | 1.5 | 1.5 | 1.5 | 1 | 1.5 | 1.5 |
1997 | 2 | 1 | 2 | 1.5 | 1 | 1 | 1 | 1.5 | 1 | 1 | 1 | 1.5 |
1998 | 1 | 2 | 1 | 1 | 1.5 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
1999 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0.5 | 0.5 | 1 | 0.5 |
2000 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
2001 | 0.5 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1.5 | 1 | 1 |
2002 | 1 | 1 | 1 | 1 | 1 | 1.5 | 1 | 2 | 1.5 | 1.5 | 1.5 | 1.5 |
2003 | 1 | 1 | 1 | 1.5 | 1 | 1 | 1 | 1.5 | 1.5 | 1.5 | 1.5 | 1 |
2004 | 1 | 2 | 1 | 1.5 | 1.5 | 2 | 1.5 | 1.5 | 1.5 | 1.5 | 2 | 2 |
2005 | 1 | 1 | 1.5 | 1 | 1 | 1.5 | 1.5 | 1 | 1 | 1.5 | 1.5 | 1.5 |
2006 | 2 | 2 | 1.5 | 1.5 | 1.5 | 1.5 | 1.5 | 1.5 | 1.5 | 1.5 | 2 | 1.5 |
2007 | 2 | 1 | 1 | 1 | 1.5 | 1 | 1.5 | 1 | 1 | 1 | 1 | 1 |
2008 | 2 | 1 | 1 | 1 | 1.5 | 1.5 | 2 | 1.5 | 2 | 1 | 2.5 | 2 |
2009 | 0.5 | 0 | 0.5 | 0.5 | 0.5 | 0 | 0 | 0 | 0 | 0 | 0 | 0.5 |
2010 | 0.5 | 0 | 0.5 | 0 | 0 | 0 | 0 | 0 | 0 | 0.5 | 0 | 0.5 |
2011 | 0 | 0 | 0.5 | 0.5 | 0.5 | 0 | 1 | 1 | 0 | 0 | 0 | 0 |
2012 | 0.5 | 1 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 0 | 0.5 | 0.5 | 0 |
2013 | 0.5 | 0 | 1 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 1 | 1.5 | 2 | 1.5 |
2014 | 2 | 2 | 2 | 2 | 2.5 | 2 | 2 | 2 | 2 | 2 | 2.5 | 2.5 |
2015 | 2 | 2 | 2 | 2 | 2 | 2.5 | 1.5 | 1.5 | 1.5 | 2 | 1.5 | 1.5 |
2016 | 2 | 2 | 1 | 2 | 2 | 2 | 1.5 | 2.5 | 3 | 2.5 | 2 | 1.5 |
2017 | 2 | 2 | 1 | 2 | 2 | 2.5 | 2 | 2 | 2 | 2 | 1.5 | 1 |
It is possible to indicate that the activity on the area has a slight increase after August, which is during Winter.
January (Summer) | 1 |
---|---|
April/May (Fall) | 1 |
July/August (Winter) | 1 |
October/November (Spring) | 1 |
months with the same number of average earthquakes. The seasons did not affect enhancements or decreases during the entire year. Although some variances could be found when we considered earthquakes above magnitude M6 this present search, showed no distinctions among the seasons.
The result is comparable with other areas, such as South America; however, in South America, the number of occurrences is the lowest at the Southern Hemisphere and a few months during several years had a lack of records in the area, such as for April (Fall), August (Winter), and September (Spring).
Yet, it seems the east side of Circum Pacific had unusual activity. In the Northern Hemisphere there were no deep-depth occurrences, in the Southern Hemisphere it happens in traplate as it happens in South America, and, further, around Fiji and Vanuatu. It seems most of the activity is in the West Pacific, in both hemispheres. Seasonality appears to be in the cases studied in this paper, restricted to the western side of the Pacific, at subduction zones.
The results concluded that the areas examined at the Northern Hemisphere had enhancements of events during Spring and Summer. For example, North Pacific had increases most at the end of Spring and the middle/end of Summer. The total of earthquakes in those regions during Spring and Summer were 60% of total activity for the entire year.
Philippines behavior has 57% of events during the Spring and Summer and the months with higher rates are May (Spring) and July (Summer).
Now, moving to the Southern Hemisphere, Indonesia had enhancements on the earthquakes during all six months, but most during Fall (March and May) and Spring (September and October) which give great variations in these results.
The analysis of the two other locations did not display the same variations during the year. One of the most significant problems working on the data from South America is the lack of recorded events in a month over several years. Our activity map had openings that perhaps did not correspond to reality. Nevertheless, earthquakes in South America do not happen in the oceans like they do in the other zones studied. It shows a system that is different from the other locations in the Northern or Southern Hemispheres. South America had an anomaly in 2015, when the earthquakes occurrences reached twenty times higher than normal. Although it would relate to the seasons, it was decided to ignore the year in our calculations. If we do, it becomes inexact to connect the earthquakes with a possible seasonality in the area. It is important to mention two months when the events are around 10%: March (Fall) and June (Winter) which is an indication that other factors may apply, but seasons are essential in this area.
The last area considered was Fiji and Vanuatu which presented an exciting result as to the first part of the year. In the months of January through July (included) there is a perfect distribution of tremors around 8% of the total for each month (7% for February). During the last part of the year, August through December, it increases to 9% by month, or 45% of the total earthquakes. Despite the encouraging results to this location in our recent paper using significant events of magnitude M6 or above, when we found Summer and Fall were 34% of variations in the area, this study found nothing when all the magnitudes of M ≥ 2.5 considered. However, the small increase in the last five months, during the entire thirty-year period, would deserve some attention.
Finally, the total number of events indicated that the Northern Hemisphere at the West side of the Pacific may demand some seasonal variation. On the other hand, there are no ultra-deep earthquakes (UDQ) on the Northeast side of the Pacific; these don’t begin to happen until lower latitudes, a little above the equator in South America. The Southeast Pacific side does not show any outstanding seasons like the Northwest, or Southwest Pacific; however, the Southwest Pacific is also a little closer to the equator than the areas considered on the east side.
Consequently, UDQ seasonality did not look to be ubiquitous; instead, it applies more to the higher latitudes or most locations nearest to the continents.
Now, compare the three Southern regions which did not presented much seasonality,
March, May, July, September, October and December each of them, present 11% of the total of earthquakes. South America (
The final conclusions for this UDQ worldwide study showed, for the initial conditions with magnitudes of M ≥ 2.5, there is evidence for seasonality at the Northwest Pacific, less evidence for the Southwest Pacific, and none for the Southeast Pacific. Such results cannot be considered final or generalized for earthquake seasonality around the globe. At this point, there are many restrictions in our studies.
It is essential to make other parameters more flexible in our calculations to enable a better statistical study. For example, considering different depths will make the system more full for possible comparisons. The only problem will always be those points around the equator where one part of the events occurs in the Northern Hemisphere and the other in the Southern Hemisphere; it makes complicate to precise seasons on the locations searched. Southern Hemisphere showed periodicity of events during the period analyzed to any magnitude searched.
The authors declare no conflicts of interest regarding the publication of this paper.
Hagen, M. and Azevedo, A. (2019) Seasonality Variability and Periodicities for Ultra-Deep Earthquakes Worldwide. Open Journal of Earthquake Research, 8, 1-18. https://doi.org/10.4236/ojer.2019.81001