I have been deluged with questions since the Ridgecrest earthquake
that are some version of “What does [quake A at location B] mean?”
“Why are there so many aftershocks near Coso?”
“What does it mean that there are earthquakes near
the Garlock fault?”
“We just had another M4.5? Does this mean we
need to be ready for a big one?”
“Are the Bay Area quakes related to Ridgecrest?”
First, for the basics about how one earthquake triggers
another, look down in this blog to my post from February 2018. It describes
what seismologists know about earthquake triggering. We actually know quite a
bit and can describe the rate of earthquakes reasonably accurately. The
variables are time from the largest earthquake (the rate goes down
approximately as 1/time), the magnitude of the triggering event and the
triggered event (small earthquakes are always much more common than big ones
and big earthquakes trigger more new events), and distance (most triggered
events are very near the fault that produce the mainshock and the rate dies off
as 1/distance^2). If you want the full details, go to the 2018 post.
In other words, we have equations to describe the rate and
that we can use to compare one aftershock sequence to another. But this is a rate. The time of an
individual earthquake is randomly distributed about that rate. So for instance
we can say there will probably be 25 to 35 earthquakes of M3 or greater in the
next week, but no idea whether the next one will be in 1 minute or tomorrow.
The USGS is creating and posting daily updates of these
People are also asking about the risk because we have the
big Garlock fault near these aftershocks. Does that make our risk worse? If another M7 were to be triggered (the
current weekly chance of that is about 1 in 300), it would likely be on the Garlock
fault so that risk is already included in the probability numbers.
People also ask about the San Andreas. It is much farther
away from the Ridgecrest earthquakes so the chance of an earthquake on it has
Compared to the average California aftershock sequence, the
Ridgecrest sequence is about average in total number but is dying off more
quickly than average. That means the chance of bigger ones is going down fast
which is why the USGS probabilities are quite a bit lower now than they were
All of the questions are some version of “Are these
aftershocks normal?” and the answer is “Yes.”
But don’t make the mistake of thinking that “normal” means another
big earthquake can’t happen. A large late aftershock is also pretty normal.
Magnitude 6 earthquakes every couple of years somewhere in Southern California are
normal. “Normal” does not mean it cannot trigger another earthquake. We are
trying to make patterns in a random distribution. Just like constellations, we
can make the patterns but they are not going to be any use in figuring out what
is coming next.
You can’t live in Southern California worrying which day will
have the big earthquake. You wear your seat belt every day, not knowing when
the next accident will be. You need to make your house safe, get your water
supply and be ready for the earthquake on any day.
I am an experimental seismologist. That means I spend a lot of time looking at data about the earth. I am not an atmospheric scientist so I cannot make detailed models for the future of the world’s climate, but I can look at data and recognize alarming trends. And the basic data for the temperature of the earth, averaged over the whole atmosphere is terrifying. The world is warming and the rate at which it is warming is getting faster.
I am also a musician and I sometimes hear the data.
This data is like a graceful minuet accelerating into a frantic jig. Of course, the increase is to be
expected because our burning of fossil fuels for energy has been increasing the
amount of CO2 in the Earth’s atmosphere. The heat in the atmosphere equals the
energy that comes in minus the energy that goes out. Energy in comes from the
sun with minor variations from rotational wobble, sunspots, etc. Energy out is the infrared heat radiation
that is given off by any body minus the amount that our atmosphere can trap.
“Greenhouse gasses” are the chemicals that absorb energy in the infrared
spectrum and thus keep some of the heat here on earth and if you increase the concentration
of greenhouse gasses, you keep more heat. Details are complex with positive and
negative feedback mechanisms, transport of heat through the ocean currents,
effects of clouds and ice, all being studied by other types of earth
scientists. But I can look at this graph
and see that the amount of carbon dioxide is up substantially and that it
correlates well with the temperatures. I find these graphs terrifying and I
struggle to understand why so many people accept this without fear.
I turn to
music to process and express my emotions. I realized early on in life that
although I love music, I would never be a great musician – one who can make a
living at it – but music continues to be the part of my life where I can
experience my emotions in more depth. I saw someone turn the temperature data
into pitch and play it on a cello. You could hear what I saw in the temperature
data. It is not a piece of music – it is a string of notes without chords or
harmony. But I started to think about using this to convey my emotions about
I play an
old string instrument called the viol (or in Italian, the viola
da gamba). A
“consort of viols” was the 17th century predecessor of the string
quartet, a small group ensemble with closely interlocking harmonies (an example here). One style of music for this
ensemble is the In Nomine, where one
instrument plays a drawn out melody and the others play intricate polyphonic
lines around that slow steady line, called the cantus firmus, or fixed song.
I decided to try to use the climate data as the cantus firmus and create music for the earth.
Turning that vision to reality has taken a few years, but I finally completed In Nomine Terra Calens: In the name of a warming Earth. This music video uses the visual and auditory arts to experience the warming Earth. It is played by four viols with one of the bass viols playing the temperature data. Thanks to Josh Lee and Ostraka for recording the piece. A friend and colleague from the Art Center College of Design, Ming Tai, led a team to create an animation of temperature data to go with the music.
that just knowing the Earth is warming is not enough. As scientists, we
understand a lot about how earthquakes, floods and other disasters will affect
people, but we have found that it is much easier for people to understand the
problem and take action when we clearly connect the consequences to the
problem. I spent a decade creating
science-based scenarios of natural disasters to provide people with the
information to make better decisions.
climate change, if we do nothing, if we continue to add CO2 to the atmosphere
through burning fossil fuels, we will change life on earth. Even though there
have been warmer times on Earth, those were times with different ecologies –
that had time to adapt to the changes in climate. The speed
with which we are changing the climate is unprecedented. The world is already
warmer by almost 2°F. Everywhere on
Earth, ecosystems are experiencing a different climate than that in which they
evolved. Within the lifetime of children now born, with no action, the climate
could be 5-10 °F warmer. What does this mean?
disasters. Heat is energy and with more energy in the atmosphere, storms will
be more severe. The strongest hurricane, the biggest daily rainfall, the
longest duration of Cat 5 winds, have all happened in the last few years.
Storms will be bigger and more devastating.
wildfires. Every ecosystem in the world will be stressed by a different
climate, mostly warmer. Wildfires are spreading through the boreal forests in
Scandinavia and Alaska. The California wildfires of the last few years are just
shortages. Farmers are already having to adapt their techniques to the changing
climate. Some places will become unfarmable.
availability crises. Some places are getting wetter and some drier. Getting
water to people will require different delivery systems than we currently have.
refugees. Some countries will be underwater as the polar ice melts. Others will
lose the ability to grow enough food for their populations. Millions, maybe
hundreds of millions of people will need to move to stay alive.
disruption? We humans have many choices to make about how we respond to these
disruptions. How will we respond to 50 million refugees?
many people, especially in America, think that dealing with climate change
means giving up modern life. We talk about individuals driving an electric car,
forgoing an airplane trip or reducing plastic use, as though that is the
solution. We don’t want to give up modern life so we don’t think about climate
change or we try to believe it isn’t really true.
answer to climate change is not a Prius and reusable grocery bag. With 7 billion people on Earth, we could give
up every aspect of modern life and not solve the problem. We still need to keep
warm in winter and move our food to where people are. The only solution is to
move forward, to a world with a carbon neutral energy system, a society where
the production of energy does not increase the carbon in the atmosphere. Until
we get to carbon neutral energy, any
life, let alone modern life, increases the CO2 in the atmosphere.
with climate change means technological innovation to create a better world. It
can be done. Solar energy is already much cheaper than it was a decade ago. When
we decided to go to the moon, we solved innumerable technical challenges and we
were proud of doing it. We did that together and we need to do it again.
individual, you might be one of the technical innovators. But every one of us
can say we want our government to fund and support the innovation. Why would we
want someone else to own the technologies that are going to be needed by the
future world? Dealing with climate change means investing in the future. Look again at the consequences of our current
trajectory. The true threat to modern life is not dealing with climate change.
I end In Nomine Terra Calens with a stripping
away of harmonies to finally land on one, lone, very high note. I end without
direction to represent the uncertain future. We stand at a decision point where
the future of the world really rests on our decisions.
Let’s talk earthquake triggering. Every time a notable earthquake occurs, I get the same questions:
How does this affect the Ring of Fire?
How does this earthquake affect California?
Does this mean a big earthquake will happen soon here?
All of these reflect the human need to make patterns, especially when faced with danger. To understand if a pattern is real, we need to use statistics to tell us if a pattern is repeatable or just coincidence. Many scientists have conducted these statistical studies and we know which ones are real.
One earthquake does make other earthquakes more likely. The slip in the quake changes the state of stress around the fault on which the first quake occurs. The likelihood of triggering another earthquake dies off with distance from the fault and the time since the quake. Mostly they are smaller and we call them aftershocks. About 5% of the time the aftershock is bigger than the first earthquake and we change the names and call the first one a foreshock.
Where the triggered earthquakes occur is a bit more complicated. To understand the results, you need to remember that earthquakes don’t happen at epicenters – they happen over a fault surface and the bigger the surface, the bigger the earthquake. From the magnitude, you can guess the length of the fault that produced the earthquake, as shown in this table.
So each earthquake has a fault length, the length of the fault that moves in that quake. Most aftershocks triggered by an earthquake will be very near its piece of fault. We use the word aftershock to described triggered earthquakes that fall within one fault length of the mainshock’s fault. For instance, a M7 earthquake will have a fault length of about 50 km. So any earthquake triggered within 50 km of any point on the mainshock’s 50-km-long fault will be called an aftershock.
Within the first week or two after a quake, we also sometimes see triggered earthquakes farther away and we use the term triggered earthquake to describe them. These might extend for 3 to 4 fault lengths. So a M7 might trigger earthquakes as far away as 150 km and a M8 might trigger earthquakes out to 800 km.
Beyond 4 fault lengths, the statistics clearly show that the rate of earthquakes doesn’t change. Mexican earthquakes have never caused a change in the rate of earthquakes in California. New Zealand earthquakes don’t trigger earthquakes in Japan. Or California. Or anywhere else. This doesn’t mean we can’t have an earthquake in California, or New Zealand or Alaska. There are M3 earthquakes several times a week in California and a magnitude 2.5 somewhere in the world every minute. But statistics of the earthquake catalogs for the last hundred years clearly show that beyond a few fault lengths the rate of earthquakes is unaffected.
So back to those questions. I’ll answer them now and you can insert whichever earthquake has just happened:
How does this [insert quake here] affect the Ring of Fire?
It doesn’t. In fact, the Ring of Fire is a literary device, not a scientific concept. When we first started exploring the world and recording earthquakes, we saw that both volcanoes and earthquakes were more common around the Pacific Ocean, and the Ring of Fire was coined to describe that. But the plate tectonics revolution in the 1960s explained why those volcanoes and earthquakes are there – they lie around the boundaries of the tectonic plates, and there are many plates around the Pacific Ocean. Now we know that earthquakes in southern California are occurring in the Pacific plate, while those in Mexico are in the Cocos or North American plate, the ones in Chile or in the Nazca plate and New Zealand is in the Australian plate. The plate motions do affect each other – on the time scale of tens of millions of years. One the time scale of one earthquake, statistics show us there is no relation.
How does this [insert quake here] affect California?
It doesn’t if it is more than a few hundred miles away.
Does [insert quake here] mean a big earthquake will happen soon here?
An earthquake somewhere else does not make a California quake more or less likely.
So when you want to make a pattern out of a group of earthquakes, remember that earthquakes happen all the time, and we need statistics to tell us if our pattern is just coincidence. Just because we want a pattern doesn’t make the pattern real.
Could the eruption of Mount Agung in Indonesia cool the earth?
Very big volcanoes can disrupt the climate around the earth. In 1783, the Laki Craters eruption in Iceland produced more than 6 times as much sulfur dioxide as Mount Pinatubo. It also got more into the stratosphere, because the bottom of the stratosphere is lower near the poles – only eight miles up. In the next year, a great freeze settled over Europe, leading to a famine that contributed to the French Revolution. The continents did not heat up as much the next summer, so the monsoons didn’t develop. This contributed to droughts that killed one-sixth of the population of Egypt, 11 million people in India and over 1 million in Japan. Could the same thing happen because of the current eruption of Mount Agung in Indonesia?
The last time Mount Agung erupted in 1963, the average global temperature dropped for a few years. This graph shows the average global temperature for the last 140 years, marking the times of five large volcanic eruptions. You can see how the world’s temperature drops for a few years after those eruptions. Some, but not all, big volcanic eruptions have caused a drop in the global temperature. What makes the difference?
The answer is in the gases that come out of the lava. Magma often has a large amount of trapped gases that get released when the it reaches the surface. The most common are water, carbon dioxide, and sulfur dioxide. Water and carbon dioxide are already so common in the atmosphere that the volcanoes do not change the global concentrations. Mount Pinatubo in 1991 released 50 million metric tons of carbon dioxide. Human activity in the United States release 100 times that – 5 billion metric tons every year. Besides, as we all know, carbon dioxide traps the infrared
radiation of heat rising form the earth and tends to make the earth hotter.
The cooling effect of volcanoes comes from pushing larger particles into the stratosphere where they block sunlight coming in. Although volcanic ash blocks sunlight, it is heavy (it is rock, even though in very small pieces) and it falls back to the earth in a few days or weeks. The biggest culprit is the sulfur dioxide. Sulfur dioxide oxidizes into sulfuric acid and condenses into sulfate aerosols. In the lower atmosphere, sulfates are washed out of the atmosphere relatively quickly by rain. But above the main climate systems, in the much drier stratosphere, particles could be transported around the world, staying aloft for years. These sulfate particles are just the right size to scatter incoming sunlight, sending some of it back into space and, consequently, cooling the ground below. Volcanic eruptions that send a lot of sulfur into the stratosphere can have a substantial impact on the global temperature. Mount Pinatubo, erupting in 1991, cooled the world by 1.5°F, with an impact that could still be felt three years later.
Mount Agung in 1963 had a similar impact to Mount Pinatubo, and it could again. The next eruption would need to also have a high concentration of sulfur dioxide, and it would need to be powerful enough to force that sulfur dioxide up into the stratosphere, 12 miles above the earth’s surface. And as we see in the graph, it doesn’t stop the global warming we are creating with greenhouse gases; it just gives us a short break in the otherwise upward trend.
You can read more about the Laki eruption and other catastrophic natural disasters in my upcoming book, The Big Ones, available for pre-order here.