No one was more preoccupied with these strange events than Kant, the great German philosopher whose name some of you may already have heard. When the earthquake occurred he was a man of twenty-four, and neither before nor after did he ever venture beyond his hometown of Königsberg; yet he collected all the accounts of this earthquake he could find, with tremendous enthusiasm. The short works he published on the phenomenon constituted the beginnings of scientific geography in Germany.1 The beginnings of seismology, at any rate. I’d like to tell you something about the path this discipline took from that portrayal of the 1755 earthquake up until today. But I must be careful that our Englishman, whose account of his experiences during the earthquake I would still like you to hear, does not get lost in the shuffle. He has been waiting impatiently; after 150 years of being ignored, he’d like once more to have his say, and has allowed me to share only a few words concerning what we now know about earthquakes. But one thing first: they are not what you think. If I could pause for a moment and ask how you would explain earthquakes, I bet the first thing you’d think of is volcanoes. It’s true that volcanic eruptions are often linked to earthquakes, or at least heralded by them. So, for 2,000 years, from the ancient Greeks through to Kant and on until about 1870, people believed that earthquakes were caused by fiery gases, steam from the Earth’s interior and suchlike. But once people began to use measuring instruments and to make calculations, whose subtlety and precision surpass anything you might imagine — and that goes for me as well — in short, once people could verify the matter, they found something altogether different, at least for large earthquakes like the one in Lisbon. They do not originate from the deepest recesses of the Earth — which we still think of as liquid, or more exactly muddy, like molten sludge — but rather from events in the Earth’s crust. The Earth’s crust is a layer roughly 3,000 kilometers thick. This layer is in perpetual upheaval; the masses within it are constantly shifting in an ongoing attempt to find equilibrium. We know some of the factors that disturb this equilibrium, and ceaseless research is being conducted to discover others.
This much is certain: the most significant shifting is a result of the continuous cooling of the Earth. This subjects the masses of rock to enormous tension, ultimately causing them to break apart and then to seek a new equilibrium by rearranging themselves, which we experience as an earthquake. Other shifting results from the erosion of mountains, which become lighter, and from alluvial deposits on the ocean floor, which becomes heavier. Storms, whirling about the Earth, especially in autumn, do their bit to rattle the planet’s surface; and finally, it remains to be determined just how the pull of celestial bodies exerts force on the Earth’s surface. But you might be thinking: if this is true, then the Earth’s crust is actually never at rest, so there must be earthquakes all the time. And you’d be right, there are. The incredible precision of the earthquake-monitoring instruments available today — in Germany alone we have thirteen seismological stations in various cities — is such that they are never completely still, which means that the Earth is always quaking, only most of the time we don’t feel it.
When, out of a clear blue sky, this quaking suddenly becomes noticeable, it’s even worse. And literally out of a clear blue sky. “Because,” writes our Englishman, who now finally gets his say,
the sun was shining in full splendor. The sky was impeccably clear, giving not the slightest sign of any natural phenomenon to come, when, between nine and ten in the morning, I was sitting at my desk and the table began to move, which was rather surprising as there was no reason at all that it should have. While I was still pondering the cause of what had just happened, the house started to shake from top to bottom. From beneath the ground came a shuddering boom, as if a storm were raging in the distance. I quickly set down my pen and jumped to my feet. The danger was great but there was still hope that it would all pass without harm; the next moment, however, would erase any uncertainty. A horrible crackling noise was heard, as if all the buildings in the city were falling down at once. My building was so jolted that the upper floors caved in, and the rooms in which I resided swayed so much that everything was turned upside down. I expected to be struck dead at any moment; the walls were crumbling, large stones fell from their cracks and the roof beams appeared to hover in midair. But at this time the sky became so dark that people couldn’t make out what was in front of them. Pitch-dark prevailed, either as a result of the immense amount of dust caused by the collapsing houses, or because of the volumes of sulfurous vapor escaping from the earth. Finally the night brightened again, the violence of the shocks relented; I collected myself as best I could and had a look around. It became clear to me that I owed my survival thus far to a small bit of luck; that is, had I been dressed I most certainly would have fled to the street and been struck dead by collapsing buildings. I quickly threw on some shoes and a coat, rushed outside and headed to St. Paul’s cemetery, where I thought I would be safest given that it sits on a hill. People no longer recognized their own streets; most could not say what had happened; everything was destroyed and no one knew what had become of their loved ones and all that they owned. From the hill of the cemetery I was then witness to a horrific spectacle: on the ocean, as far as the eye could see, countless ships surged with the waves, crashing into one another as if a massive storm were raging. All of a sudden the huge seaside pier sank, along with all the people who believed they would be safe there. The boats and vehicles so many people used to seek rescue fell equal prey to the sea.2
As we know from other accounts, it was about an hour after the second and most devastating seismic shock that the massive swell, twenty meters high, which the Englishman saw from afar, came tumbling over the city. When the tidal wave receded, the Tagus riverbed suddenly appeared completely dry; its recoil was so powerful that it took all the river’s water with it. “When evening lowered over the desolated city,” the Englishman concludes, “it looked like a sea of fire: the light was so bright, you could read a letter by it. The flames soared from at least a hundred different points and raged for six days, consuming whatever the earthquake had spared. Petrified in anguish, thousands stood mesmerized before the city, as wives and children beseeched all saints and angels for help. All the while the earth continued to quake with greater or lesser force, often for a quarter of an hour without cease.”
So much for this fatal day, November 1, 1755. The disaster it brought is one of the very few before which mankind is as powerless today as it was 170 years ago. Here, too, technology will find a way out, albeit an indirect one: through prediction. For the time being, however, it seems that the sensory organs of some animals are still superior to our finest instruments. Dogs in particular will exhibit unmistakable agitation for days before the onset of earthquakes, which is why they are deployed to provide assistance to earthquake stations in vulnerable regions. And with that, my twenty minutes are up; I hope they didn’t go by too slowly for you.