Introduction

This case study is the capstone project required to achieve the Data Analytics Professional Certificate offered by Google upon successful completion of this course.

Earthquakes and tsunamis have had and will continue to have a major impact on human life on planet Earth throughout history. That is why I chose to analyze the Global Significant Earthquake Database (GSED) made available by the National Centers for Environmental Information (NCEI)/World Data System (WDS) through the National Oceanic and Atmospheric Administration (NOAA)

The GSED is a global listing of 6,273 earthquakes from 2150 BC to September 2021 CE.

The purpose of this project is to provide and quantify some measurable insights into the nature, characteristics, and impact of global earthquakes from 1900 CE to 2021 CE.

Objectives of this analysis

  1. Present an interactive world map showing all earthquakes and tsunamis, color coded, with magnitude filters. The user must also be able to click on each circle that represents an earthquake and obtain data on magnitude, intensity, year when it occurred, and total deaths.
  2. Strongest earthquakes and tsunamis overall.
  3. Deadliest earthquakes and tsunamis overall.
  4. Breakdown of total earthquakes and tsunamis per year and average.
  5. Breakdown of earthquakes and tsunamis by magnitude and their focal depth range.
  6. Summary of earthquakes/tsunamis by magnitude scales.
  7. Correlation between magnitude/intensity and focal depth.
  8. Countries with most earthquakes and tsunamis, including total deaths.
  9. Deadliest earthquakes and tsunamis by country, counted.
  10. Deadliest earthquakes and tsunamis by country, with magnitude.
  11. Deadliest earthquakes and tsunamis by magnitude, with year.

Data description

The GSED is a dataset of 6,273 entries and 47 total columns (variables).

In order to be classified as a significant earthquake, the event must meet at least one of the following criteria: moderate damage (approximately $1 million or more), 10 or more deaths, magnitude 7.5 or greater, Modified Mercalli Intensity X or greater, or the earthquake generated a tsunami.

This database provides information on the date and time of occurrence, latitude and longitude, focal depth, magnitude, maximum MMI intensity, and socio-economic data such as the total number of casualties, injuries, houses destroyed, and houses damaged, and $ dollage damage estimates. References, political geography, and additional comments are also provided for each earthquake. If the earthquake was associated with a tsunami or volcanic eruption, it is flagged and linked to the related tsunami event or significant volcanic eruption.

Earthquakes data concepts

The first known earthquake detector was invented in 132 CE by the Chinese astronomer and mathematician Chang Heng. He called it an “earthquake weathercock.” And, in 136 CE a Chinese scientist named Choke updated the meter and called it a “seismoscope”.

Seismologists study earthquakes by looking at the damage that was caused and by using seismometers. A seismometer is an instrument that records the shaking of the Earth’s surface caused by seismic waves. The term seismograph usually refers to the combined seismometer and recording device.

Since the energy released by an earthquake travels in a wave, and earthquakes are actually recorded by a seismographic network, there are many different ways to measure different aspects of an earthquake. Magnitude is the most common measure of an earthquake’s “size” or strength , and the Moment Magnitude is considered the most accurate scientific scale (the Richter scale is an outdated method that is no longer used for large earthquakes). Also, the magnitude does not depend on where the measurement is made.

The GSED provides the following logarithmic magnitudes which valid values go from 0 to 9.9:
* Mw - It is based on the moment magnitude scale
* Ms - It is the surface-wave magnitude of the earthquake
* Mb - It is the compressional body wave (P-wave) magnitude
* Ml - It was the original magnitude relationship defined by Richter and Gutenberg for local earthquakes in 1935
* Mfa - These magnitudes are computed from the felt area, for earthquakes that occurred before seismic instruments were in general use

Because of the logarithmic basis of these scales, each whole number increase in magnitude represents a tenfold increase in measured amplitude. As an estimate of energy, each whole number step in the magnitude scale corresponds to the release of about 31 times more energy than the amount associated with the preceding whole number value.

For example, the following is a comparison of the strength of earthquakes of different magnitudes based on a magnitude 4 earthquake:

  • A magnitude 5 is 10 times stronger
  • A magnitude 6 is 100 times stronger
  • A magnitude 7 is 1000 times stronger
  • A magnitude 8 is 10,000 times stronger

On the other hand, intensity scales like the Modified Mercalli Scale (valid values go from 1 to 12) measure the amount of shaking at a particular location. An earthquake causes many different intensities of shaking in the area of the epicenter where it occurs. So the intensity of an earthquake will vary depending on where you are. The Mercalli Scale is based on observable earthquake damage.The GSED provides the Modified Mercalli (MMI) Intensity when available.

So, from a scientific standpoint, the magnitude scale is based on seismic records while the Mercalli’ scale is based on observable data which can be subjective, as illustrated in Fig. 13.

For the purpose of this analysis, I will be focusing on their equivalent magnitude. This magnitude is chosen from the available magnitude scales in this order: Mw, Ms, Mb, Ml, and Mfa.

Generally, earthquakes of magnitude 6 and above are the ones for concern. When nearby, they can cause shaking intensities that can begin to break chimneys and cause considerable damage to the most seismically vulnerable structures, such as non-retrofitted brick buildings.

Earthquake magnitude scales

Fig. 1

Modified Mercalli Intensity (MMI) correlation with magnitude

Magnitude Typical Maximum MMI Intensity
1.0 - 3.0 I
3.0 - 3.9 II - III
4.0 - 4.9 IV - V
5.0 - 5.9 VI - VII
6.0 - 6.9 VII - IX
7.0 and higher VII or higher

Considering that:

  • Earthquake magnitudes prior to 1890 have been estimated by looking at the physical effects (such as amount of faulting, landslides, sandblows or river channel changes) plus the human effects (such as the area of damage, or felt reports, or how strongly a quake was felt) and comparing them to modern earthquakes,
  • The first seismographs came into use about 1890, and
  • In 1935 Charles Richter developed the magnitude scale

I decided to choose the study period of 1900 to 2021 because of the amount and accuracy of data available, so I filtered earthquakes from 1900 to 2021 only. And this is the base file used for this analysis (the number of earthquakes in the GSED database before 1900 CE is 2,490 (39.7%) and after 1900 CE is 3,783 (60.3%)).

In the new data set from 1900, the following values have been found missing for the most important variables (shown between parenthesis) used in this analysis:

  • Country (country): 0
  • Year (year): 0
  • Tsunami (flag_tsunami): 2,735 (These missing values may be because there was no tsunami associated with this earthquake, or due to a missing value itself)
  • Magnitude (eq_primary): 300
  • Intensity (intensity): 2,231
  • Focal depth (focal_depth): 706
  • Latitude (latitude): 10
  • Longitude (longitude): 7
  • Total deaths (total_deaths): 2,416

Analysis and Visualizations

1. Interactive world map showing all earthquakes and tsunamis grouped in clusters, color coded and filtered by magnitude

The interactive world map below offers the option to filter earthquakes by magnitude, and is also a very useful source of information.

On this map individual earthquakes are represented by color coded circles following this pattern:

  • 9.0 - 9.9 ==> Gray (5 occurrences)
  • 8.0 - 8.9 ==> Magenta (122 occurrences)
  • 7.0 - 7.9 ==> Red (1,031 occurrences)
  • 6.1 - 6.9 ==> Maroon (1,093 occurrences)
  • 5.5 - 6.0 ==> Dark Orange (909 occurrences)
  • 1.6 - 5.4 ==> Blue (320 occurrences)
  • NA (Most significant earthquakes with missing magnitudes) ==> Cyan (293 occurrences)
    Note: 10 earthquakes were not included on this map because they lacked latitude, of these, 7 also lacked longitude values.

On the map’s top right position there are magnitude check mark boxes that filter earthquakes by the selected magnitudes.

There are two ways to zoom in and out, either by using the “+” and “-” signs on the top left, or by scrolling up and down with the mouse wheel in the area map. To scroll up and down the page, just move the cursor outside the map. You can also click and drag to move the map in any direction.

The map also groups the earthquakes on each magnitude layer in clusters that depend on the zoom level, and adjust themselves automatically to show the number of earthquakes grouped in each cluster. In this way the earthquakes visualization doesn’t look too crowded.

Once an individual earthquake colored circle is shown, a label containing its associated data: magnitude, intensity, year, depth and deaths, is displayed by just hovering the mouse cursor on that colored circle. But, to get a better view of these values you can click on the circle as soon as the label is displayed to see this values on a steady bigger box. To close this box, you can click on the “x” inside the box, or just click outside.

Also, as previously mentioned, it was found that 300 earthquakes in the GSED did not have a magnitude value of any kind listed. These earthquakes are included in the “NA” layer.

The following is an option map with no clusters, to view individual earthquakes without having to zoom in to the maximum level. This option may be more useful when viewing just one selected layer.

2. Strongest earthquakes and tsunamis overall

The following table below shows an overview of earthquake and tsunami data.

Fig. 2

A breakdown of the data above for the 12 strongest and deadliest earthquakes is presented in the next two tables.

The 12 strongest earthquakes/tsunamis
Year Tsunami Magnitude Intensity Country Total deaths
1960 Tsu 9.5 12 CHILE 2226
1964 Tsu 9.2 10 USA 139
2011 Tsu 9.1 NA JAPAN 18429
2004 Tsu 9.1 NA INDONESIA 227899
1952 Tsu 9.0 7 RUSSIA 10000
2010 Tsu 8.8 9 CHILE 558
1965 Tsu 8.7 6 USA NA
1922 Tsu 8.7 11 CHILE 700
2012 Tsu 8.6 NA INDONESIA 10
2005 Tsu 8.6 NA INDONESIA 1313
1957 Tsu 8.6 NA USA 2
1950 Tsu 8.6 11 INDIA 1530

Note: The “Tsu” data under the “Tsunami” column indicates an earthquake that also involved a tsunami.

3. Deadliest earthquakes and tsunamis overall

The 12 deadliest earthquakes/tsunamis
Year Tsunami Magnitude Intensity Country Total deaths
2010 Tsu 7.0 NA HAITI 316000
1976 NA 7.5 11 CHINA 242769
2004 Tsu 9.1 NA INDONESIA 227899
1920 Tsu 8.3 12 CHINA 200000
1923 Tsu 7.9 NA JAPAN 142807
1948 NA 7.2 10 TURKMENISTAN 110000
2008 Tsu 7.9 9 CHINA 87652
1908 Tsu 7.0 11 ITALY 80000
2005 NA 7.6 8 PAKISTAN 76213
1970 Tsu 7.9 10 PERU 66794
1935 Tsu 7.5 10 PAKISTAN 60000
1927 NA 7.6 11 CHINA 40912

Note: The “NA” value under the “Tsunami” column indicates only an earthquake.

Observations

  • All the strongest earthquakes also involved tsunamis
  • The deadliest tsunamis/earthquakes are not necessarily the most powerful in magnitude. The deadliest tsunami/earthquake in history was 7.0 in Haiti (2010), with the highest death toll in history from a tsunami or earthquake: 316,000
  • On the other hand, the most powerful in magnitude tsunamis/earthquakes are not necessarily the deadliest, which depend on the location among other factors
  • The only exception is the tsunami/earthquake occurred in Indonesia in 2004, which combined a powerful 9.1 magnitude with the second highest death toll for a tsunami/earthquake: 227,899. So, this is the only tsunami/earthquake these two tables have in common
  • The deadliest earthquake that did not include a tsunami occurred in China in 1976 with a death toll of 242,769 and a magnitude of 7.5

4. Breakdown of total earthquakes and tsunamis per year and average

This data was already mentioned above and now it is shown as visualization.

Fig. 3

Fig. 4

5. Breakdown of earthquakes and tsunamis by magnitude and their focal depth range

From the two graphics below, we can see the amount of earthquakes and tsunamis peak between the magnitudes 7.0 and 7.5. And from a statistical point of view, these graphs may follow a specific distribution, which may be further investigated.

Besides, earthquakes involving tsunamis don’t seem to have focal depths beyond 130 Km, while earthquakes may reach focal depths up to 700 Km. In general, shallow earthquakes generally tend to be more damaging than deeper ones. It may be because seismic waves from deep earthquakes have to travel farther to the surface losing energy along the way.

Also, using the world map filter, we find out the 2004 devastating tsunami in Indonesia (which originated in the Indian Ocean) was 9.1 and had a focal depth of 30 Km only, which supports the previous claim.

Fig. 5

Fig. 6

6. Summary of earthquakes/tsunamis by magnitude scales

The following table shows the average per year of earthquakes and tsunamis for each category in the magnitude scale:

Fig. 7

We can see that the ‘Major’ and ‘Strong’ earthquakes are the most frequent. But the average for the ‘Rare-Great’ does not really reflect the reality (see notes for chart below for clarification).

And, the next visualization attempts to show the distribution of earthquakes/tsunamis per year for each category in the magnitude scale: Rare-Great, Great, Major, Strong and Moderate earthquakes. The ‘Light’ and ‘Minor’ categories are not included since they are not really relevant, and to avoid cluttering the visualization too much. Each dot represents an earthquake.

On the other hand, individual dots for the ‘Major’, ‘Strong’, and ‘Moderate’ categories are not shown because they are too many. So, only the distribution lines are displayed.

Fig. 8

What is interesting in this visualization is the ‘R-Great’ category summarized in the following table, and ordered by year starting with the most recent:

Rare-Great earthquakes/tsunamis
Year Tsunami Magnitude Intensity Country Total deaths
2011 Tsu 9.1 NA JAPAN: HONSHU 18429
2004 Tsu 9.1 NA INDONESIA: SUMATRA: ACEH: OFF WEST COAST 227899
1964 Tsu 9.2 10 ALASKA 139
1960 Tsu 9.5 12 CHILE: PUERTO MONTT, VALDIVIA 2226
1952 Tsu 9.0 7 RUSSIA: KAMCHATKA PENINSULA 10000

As we can see:

  • There are only 7 ‘Rare-Great’ earthquakes recorded in the entire history of this database, which is why they are called by this name, however 5 of them have occurred since 1952
  • All 5 of them included tsunamis
  • Although the average (from 1900 to 2021) of these earthquakes is 1 every 25 years, the reality is that the first one recorded since 1900 occurred in 1952 (Russia-Kamchatka Peninsula), and the last one in 2011 (Japan) in a time span of just 59 years
  • Of all these, the deadliest one was the 2004 Indonesian tsunami (227,899 deaths), followed by the 2011 Japanese tsunami (18,429 deaths)
  • The most powerful of these 5, and of all history, was the one that happened in Chile, with a magnitude of 9.5 and 2,226 deaths

7. Correlation between magnitude/intensity and focal depth

Earth is composed of four distinct layers: The inner core, the outer core, the mantle and the crust, which is what we live on.
And, Earth’s crust is like the shell of a hard-boiled egg. It is extremely thin, cold and brittle compared to what lies below it.
Besides, Earth’s crust ranges from 5 to 100 kilometers thick depending on oceanic versus continental crust (as seen in the picture below). The thin oceanic crust is denser than the thicker continental crust. In a very general way, it is thought that Earth’s crust “floats” on top of the soft plastic-like mantle below.

Fig. 9

Earthquakes occur in the crust or upper mantle, which ranges from the earth’s surface to about 800 kilometers deep (about 500 miles).

The strength of shaking from an earthquake diminishes with increasing distance from the earthquake’s source, so the strength of shaking at the surface from an earthquake that occurs at 500 km deep is considerably less than if the same earthquake had occurred at 20 km depth.

Most parts of the world experience at least occasional shallow earthquakes which originate within 60 km (40 miles) of the Earth’s outer surface. In fact, the great majority of earthquakes focal depths are shallow. Of the total energy released in earthquakes, 12 percent comes from intermediate earthquakes, that is, quakes with a focal depth ranging from about 60 to 300 km. About 3 percent of total energy comes from deeper earthquakes, up to 700 km.

For all earthquakes studied, the graphic below confirms that the vast majority of earthquakes originate in the crust:

  • Shallow (0-60Km): 87.9 %
  • Intermediate (60-300Km): 10.7 %
  • Deep (300-700Km): 1.4 %

Fig. 10

Next, the intensity graphic follows a similar pattern to the magnitude one. Nevertheless, deep earthquakes do not seem to have caused much trouble, reaching a maximum intensity level of VI (6) only. These, and the other deep earthquakes (in the previous graphic) recorded a magnitude of 7 and higher, and may have actually reached medium intensity levels mostly according to the Intensity vs. Magnitude graphic below in this section.

Fig. 11

On the other hand, the MMI intensity scale is from 1 to 12 (whole numbers only). The lesser degrees of the MMI scale generally describe the manner in which the earthquake is felt by people. The greater numbers of the scale are based on observed structural damage.

This table gives MMIs that are typically observed at locations near the epicenter of the earthquake:

Fig. 12

In the next graphic we see all the earthquakes mapped according to their magnitude (fractional) and intensity (no-fractional) values.

However, when analyzing the Mercally’s scale it is very important to keep in mind these facts:

  • On the one hand, the Mercalli Scale is based on observable earthquake damage. It depends on the observer, and therefore it may be subjective.
  • On the other hand, in some cases, the actual reported damages and loss of lives will depend on the quality of construction and location of houses, buildings and other structures. Obviously, the damage will be devastating in the poorest countries. In general, they will score higher on this scale than a developed country. A clear example of this situation is the comparison of tsunamis that occurred in Japan and Haiti described later in section 8.

With this in mind, we may understand better the following observations based on the Fig. 13 below:

  • The same intensity can be reached with a wide range of magnitudes

  • A level IX (9) intensity earthquake is considered “violent”, with the upper levels 10-12 considered “extreme”, but we can see that a violent level of damage can be reached starting with a 5.0 magnitude earthquake. And the extreme ones starting with a 5.5 magnitude earthquake only.

  • On the other hand, we can have powerful earthquakes between the magnitudes 8 and 9 that only reach an intensity of 7 or less.

  • An extreme level XII (12) intensity -total damage- earthquake can be caused by a 6.8 magnitude earthquake, and of course, it also follows the natural logic: more powerful = more damage.

Fig. 13

Additionally, and as a complement to the previous information, we can see that Fiji, Peru and Russia have recorded the deepest focal depth earthquakes, as well as the most number of them: 9, 8 and 8 respectively ordered by their count.

Fig. 14

8. Countries with most earthquakes and tsunamis, including total deaths

Note: In this and the following graphics, the term earthquakes also include tsunamis, but I have also provided a similar visualization for tsunamis only right below each one of them.

I have also chosen to show only the top 20 countries on the list to keep the chart from looking too cluttered. For each country bar, the total number of earthquakes and tsunamis is printed, and right next to this figure and in parentheses is the total number of deaths.

So, the country with the most earthquakes since 1900 is China, with 365 occurrences and a total death toll of 650,647 (Fig. 14); followed by Indonesia and Japan. It seems this region of planet earth experiences the most amount of earthquakes and their fatalities.

But, regarding tsunamis China falls to place 17, having experienced only 14 of them, which seem to have been very deadly because of the 289,752 fatalities registered (Fig. 17).

On the other hand, Japan raises to 1st place in tsunamis, with 158 of them, but the total deaths (178,616) is 61% only of the ones in China (289,752); even though the difference in tsunamis is 11.3 times bigger: 158 vs. 14. So, it looks like Japan has learned to cope to some extent with this powerful force of nature which they can not avoid.

On the other hand, Haiti, that has experienced the deadliest tsunami since 1900, does not show up in this list because it had only 2 tsunamis in the last 122 years. And this visualization is about the most number of tsunamis. For this reason, I am providing next a second set of these related graphics in Figs. 16 and 17.

Fig. 15

Fig. 16

9. Deadliest earthquakes and tsunamis by country

The following two graphics provide additional information to the previous ones. They just rank both earthquakes and tsunamis by their overall death toll.

Haiti shows up in these graphics and alternates with China in the first two places. Haiti is second in earthquake fatalities, but first in tsunami fatalities. That is because of the 2010 earthquake/tsunami that caused the highest number of deaths of all tsunamis since 1900: 316,000.

And, this is revealing:

  • Japan has experienced 158 tsunamis in the magnitude range of 5.6 up to 9.1 (in 2011), with 178,616 total fatalities.

  • Haiti has experienced 2 tsunamis only with 318,248 fatalities:

    • The 2010 tsunami ==> magnitude 7 and 316,000 deaths
    • The 2021 tsunami ==> magnitude 7.2 and 2,248 deaths

This is that Japan has had 79 times more tsunamis than Haiti, but with 56.1 % of Haiti fatalities only.
Perhaps, this reveals in numbers the sheer difference between two extreme economies: A rich and developed country at one extreme, and a country at the other extreme in poverty.

Fig. 17

Fig. 18

10. Deadliest earthquakes and tsunamis by country, with magnitude

This set of graphics complement my previous observations: China, Haiti and Indonesia share the first 3 places in the last two sets of visualizations, and the reasons are there.

Fig. 19

Fig. 20

11. Deadliest earthquakes and tsunamis by magnitude, with year

This last set of graphics is interesting because it supports the visualization of earthquakes and tsunamis by magnitude in section 5. It shows that the earthquakes and tsunamis of magnitude 7 to 7.9 have been the most frequent and the ones that have claimed the most amount of lives. Of course, followed by the far less frequent (but 100 and 10 times stronger) earthquakes and tsunamis of higher magnitudes: 9.1 and 8.3.

Fig. 21

Fig. 22

Each person may take and use any part of this information as they see fit. The intent is to provide useful earthquake information in a way that is accessible and easy to follow for anyone interested in taking a look at some statistics information about earthquakes recorded from 1900 to September/2021.

Of course, more work can be done on the GSED database, this is just a small sample within the scope of this capstone project only. And, someone else may draw more conclusions from these visualizations as well. The ones I provided are just a few examples. Thank you for reading it.