diff --git a/bbp/comps/lf_seismograms.py b/bbp/comps/lf_seismograms.py
index 4e0e043..f704fb2 100644
--- a/bbp/comps/lf_seismograms.py
+++ b/bbp/comps/lf_seismograms.py
@@ -75,12 +75,14 @@ class LFSeismograms(object):
     tmpdir directory
     """
 
-    def __init__(self, i_seis_dir, i_r_stations, sim_id=0):
+    def __init__(self, i_seis_dir, i_r_stations,
+                 allow_negative_timestamps=False, sim_id=0):
         """
         Initialize class variables
         """
         self.seis_dir = i_seis_dir
         self.r_stations = i_r_stations
+        self.allow_negative_timestamps = allow_negative_timestamps
         self.sim_id = sim_id
 
     def run(self):
@@ -108,4 +110,28 @@ def run(self):
                                          "%d.%s-lf.bbp" % (int(self.sim_id),
                                                                station_name))
             print("Copying LF file for station %s..." % (station_name))
-            shutil.copy2(a_input_file, a_output_file)
\ No newline at end of file
+
+            if self.allow_negative_timestamps:
+                shutil.copy2(a_input_file, a_output_file)
+            else:
+                # Copy LF seismograms but remove points with t<0
+                fp_in = open(a_input_file, 'r')
+                fp_out = open(a_output_file, 'w')
+                for line in fp_in:
+                    pieces = line.split()
+                    try:
+                        if pieces[0] == '#' or pieces[0] == '%':
+                            fp_out.write(line)
+                        elif float(pieces[0]) < -0.0001:
+                            continue
+                        elif float(pieces[0]) < 0.0001:
+                            fp_out.write("0.0\t%s\t%s\t%s\n" % (pieces[1],
+                                                                pieces[2],
+                                                                pieces[3]))
+                        else:
+                            fp_out.write(line)
+                    except ValueError:
+                        fp_out.write(line)
+                fp_in.close()
+                fp_out.flush()
+                fp_out.close()