earthquakes // source http://jsbin.com/vugaxo

<!DOCTYPE html>
<meta charset="utf-8">
<title>earthquakes</title>
<style>
body {
  font: 10px sans-serif;
}
.dot {
  stroke: #000;
}
</style>
<body>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script src="https://d3js.org/d3-scale-chromatic.v1.min.js"></script>
<script>
var margin = {top: 20, right: 20, bottom: 30, left: 40},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;
var x = d3.scaleLinear()
    .range([0, width]);
var y = d3.scaleLinear()
    .range([height, 0]);
//var color = d3.scaleOrdinal(d3.schemeSpectral);
var color = d3.scaleSequential(d3.interpolateRainbow);
var xAxis = d3.axisBottom()
    .scale(x);
var yAxis = d3.axisLeft()
    .scale(y);
var svg = d3.select("body").append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom)
  .append("g")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");
var url = "https://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/all_week.geojson";
d3.json(url, function(error, json) {
  if (error) throw error;
  var data = json.features.map(function(d) {
    return [ d.geometry.coordinates[0], d.geometry.coordinates[1], d.properties.mag ];
  });
  x.domain(d3.extent(data, function(d) { return d[0]; })).nice();
  y.domain(d3.extent(data, function(d) { return d[2]; })).nice();
  color.domain(d3.extent(data, function(d) { return d[1]; }));
  svg.append("g")
      .attr("class", "x axis")
      .attr("transform", "translate(0," + height + ")")
      .call(xAxis)
    .append("text")
      .attr("class", "label")
      .attr("x", width)
      .attr("y", -6)
      .style("text-anchor", "end")
      .text("Longitude");
  svg.append("g")
      .attr("class", "y axis")
      .call(yAxis)
    .append("text")
      .attr("class", "label")
      .attr("transform", "rotate(-90)")
      .attr("y", 6)
      .attr("dy", ".71em")
      .style("text-anchor", "end")
      .text("Magnitude");
  svg.selectAll(".dot")
      .data(data)
    .enter().append("circle")
      .attr("class", "dot")
      .attr("r", 3.5)
      .attr("cx", function(d) { return x(d[0]); })
      .attr("cy", function(d) { return y(d[2]); })
      .style("fill", function(d) { return color(d[1]); });
  var legend = svg.selectAll(".legend")
      .data(d3.range(10 * Math.round(color.domain()[1] / 10), 10 * Math.round(color.domain()[0] / 10), -10))
    .enter().append("g")
      .attr("class", "legend")
      .attr("transform", function(d, i) { return "translate(0," + i * 20 + ")"; });
  legend.append("rect")
      .attr("x", width - 18)
      .attr("width", 18)
      .attr("height", 18)
      .style("fill", color);
  legend.append("text")
      .attr("x", width - 24)
      .attr("y", 9)
      .attr("dy", ".35em")
      .style("text-anchor", "end")
      .text(function(d) { return d; });
});
</script>
<script id="jsbin-source-html" type="text/html"><!DOCTYPE html>
<meta charset="utf-8">
<title>earthquakes</title>
<style>
body {
  font: 10px sans-serif;
}
.dot {
  stroke: #000;
}
</style>
<body>
<script src="//d3js.org/d3.v4.min.js"><\/script>
<script src="//d3js.org/d3-scale-chromatic.v1.min.js"><\/script>
<script>
var margin = {top: 20, right: 20, bottom: 30, left: 40},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;
var x = d3.scaleLinear()
    .range([0, width]);
var y = d3.scaleLinear()
    .range([height, 0]);
//var color = d3.scaleOrdinal(d3.schemeSpectral);
var color = d3.scaleSequential(d3.interpolateRainbow);
var xAxis = d3.axisBottom()
    .scale(x);
var yAxis = d3.axisLeft()
    .scale(y);
var svg = d3.select("body").append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom)
  .append("g")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");
var url = "https://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/all_week.geojson";
d3.json(url, function(error, json) {
  if (error) throw error;
  var data = json.features.map(function(d) {
    return [ d.geometry.coordinates[0], d.geometry.coordinates[1], d.properties.mag ];
  });
  x.domain(d3.extent(data, function(d) { return d[0]; })).nice();
  y.domain(d3.extent(data, function(d) { return d[2]; })).nice();
  color.domain(d3.extent(data, function(d) { return d[1]; }));
  svg.append("g")
      .attr("class", "x axis")
      .attr("transform", "translate(0," + height + ")")
      .call(xAxis)
    .append("text")
      .attr("class", "label")
      .attr("x", width)
      .attr("y", -6)
      .style("text-anchor", "end")
      .text("Longitude");
  svg.append("g")
      .attr("class", "y axis")
      .call(yAxis)
    .append("text")
      .attr("class", "label")
      .attr("transform", "rotate(-90)")
      .attr("y", 6)
      .attr("dy", ".71em")
      .style("text-anchor", "end")
      .text("Magnitude");
  svg.selectAll(".dot")
      .data(data)
    .enter().append("circle")
      .attr("class", "dot")
      .attr("r", 3.5)
      .attr("cx", function(d) { return x(d[0]); })
      .attr("cy", function(d) { return y(d[2]); })
      .style("fill", function(d) { return color(d[1]); });
  var legend = svg.selectAll(".legend")
      .data(d3.range(10 * Math.round(color.domain()[1] / 10), 10 * Math.round(color.domain()[0] / 10), -10))
    .enter().append("g")
      .attr("class", "legend")
      .attr("transform", function(d, i) { return "translate(0," + i * 20 + ")"; });
  legend.append("rect")
      .attr("x", width - 18)
      .attr("width", 18)
      .attr("height", 18)
      .style("fill", color);
  legend.append("text")
      .attr("x", width - 24)
      .attr("y", 9)
      .attr("dy", ".35em")
      .style("text-anchor", "end")
      .text(function(d) { return d; });
});
<\/script></script>

Modified http://d3js.org/d3.v4.min.js to a secure url

Modified http://d3js.org/d3-scale-chromatic.v1.min.js to a secure url

https://d3js.org/d3.v4.min.js

https://d3js.org/d3-scale-chromatic.v1.min.js

https://d3js.org/d3.v4.min.js

https://d3js.org/d3-scale-chromatic.v1.min.js